perfusion index thesis

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• Indian J Anaesth
• v.61(8); 2017 Aug

Perfusion index as a predictor of hypotension following spinal anaesthesia in lower segment caesarean section

Devika rani duggappa.

Department of Anaesthesia, Bangalore Medical College and Research Institute, Bengaluru, Karnataka, India

Aanchal Dixit

Rinita paul, rs raghavendra rao, background and aims:.

Perfusion index (PI) is a new parameter tried for predicting hypotension during spinal anaesthesia for the lower segment caesarean section (LSCS). This study aimed at investigating the correlation between baseline perfusion index and incidence of hypotension following SAB in LSCS.

In this prospective observational study, 126 parturients were divided into two groups on the basis of baseline PI. Group I included parturients with PI of ≤3.5 and Group II, parturients with PI values >3.5. Spinal anaesthesia was performed with 10 mg of injection bupivacaine 0.5% (hyperbaric) at L3–L4 or L2–L3 interspace. Hypotension was defined as mean arterial pressure <65 mmHg. Statistical analysis was performed using Chi-square test, independent sample t -test and Mann–Whitney U-test. Regression analysis with Spearman's rank correlation coefficient was done to assess the correlation between baseline PI and hypotension. Receiver operating characteristic (ROC) curve was plotted for PI and occurrence of hypotension.

The incidence of hypotension in Group I was 10.5% compared to 71.42% in Group II ( P < 0.001). There was significant correlation between baseline PI >3.5 and number of episodes of hypotension ( r s 0.416, P < 0.001) and total dose of ephedrine ( r s 0.567, P < 0.001). The sensitivity and specificity of baseline PI of 3.5 to predict hypotension was 69.84% and 89.29%, respectively. The area under the ROC curve for PI to predict hypotension was 0.848.

Conclusion:

Baseline perfusion index >3.5 is associated with a higher incidence of hypotension following spinal anesthesia in elective LSCS.

INTRODUCTION

Hypotension following spinal anaesthesia results from the sympathetic blockade and decreased cardiac output.[ 1 ] Pregnant women are more sensitive to local anaesthetics, less responsive to vasopressors and have lower mean arterial pressure (MAP) at term.[ 2 ] Hence, parturients can develop profound hypotension following central neuraxial blockade for the lower segment caesarean section (LSCS).

Non-invasive blood pressure (NIBP) measurement is the standard method of monitoring intraoperative haemodynamics. However, beat to beat variation in perfusion dynamics cannot be measured by this method and limits its efficacy.

Perfusion index (PI) is defined as the ratio of pulsatile blood flow to non-pulsatile blood flow in the peripheral vascular tissue, measured using a pulse oximeter based on the amount of Infrared light absorbed.[ 3 ] Hence, PI can be used to assess perfusion dynamics and is being considered as a non-invasive method to detect the likelihood of development of hypotension following subarachnoid block (SAB).[ 4 , 5 , 6 ] Various studies carried out previously have employed perfusion index to assess haemodynamic parameters. However, there are limited data regarding its use for prediction of the incidence of hypotension occurring as a result of the central neuraxial blockade. We conducted this study to determine whether a baseline PI >3.5 predicts the development of hypotension after spinal anaesthesia in parturients.

The prospective observational study was conducted from June 2014 to October 2014. Approval for the study was obtained from the Institutional Ethics Committee. Informed written consent was obtained from every participant in the study.

The study included parturients between 20 and 35 years of age posted for elective caesarean section. We hypothesised that parturients with higher baseline PI would have a higher incidence of hypotension. Anticipating equal distribution of baseline PI on either side of cut-off point of 3.5 suggested in a study by Toyama et al .,[ 7 ] we conducted a pilot study in 15 parturients and found a difference in the incidence of hypotension to be 20% when those 15 patients were divided into two groups based on cut-off point of 3.5 (Group I PI ≤3.5 [eight patients] and PI >3.5 [seven patients]). Keeping the confidence interval at 95%, a minimum of 120 parturients would be required, to achieve a power of 80%, if the same result had to be reproduced. We enrolled 126 parturients for the study. Parturients involved in the pilot study were not considered for final analysis. Parturients with placenta praevia, preeclampsia, cardiovascular or cerebrovascular disease, gestational diabetes, body mass index ≥40, gestational age <36 or >41 weeks, contraindications to spinal anaesthesia and those requiring emergency LSCS were excluded from the study. Standard monitoring with electrocardiography, automated NIBP, and pulse oximetry (SpO 2 ) was performed for baseline values and intraoperative monitoring. The perfusion index was measured in the supine position using a specific pulse oximeter probe (Masimo Radical 7®; Masimo Corp., Irvine, CA, USA) which was attached to the left index finger of all parturients to ensure uniformity in measured PI values.

This was a double-blinded study. The baseline haemodynamic values including PI were recorded in the supine position by an anaesthesiologist who was not involved in the further intraoperative monitoring of the patient. Those with a baseline perfusion index of ≤3.5 fell into Group I and those with a perfusion index of >3.5 fell into Group II.[ 7 ]

Intravenous (IV) access was established in the left upper limb. Each parturient was prehydrated with 500 ml of Ringer lactate over 20 min. After prehydration, the baseline values were recorded. While administering neuraxial blockade, the Masimo® pulse oximeter was disconnected to prevent observer bias and SpO 2 was recorded using a different pulse oximeter. Spinal anaesthesia was performed by an anaesthesiologist blinded to the baseline PI values, using Quincke's 25-gauge spinal needle in left lateral decubitus position with 10 mg of injection bupivacaine 0.5% (hyperbaric) at the L3–L4 or L2–L3 interspace. The parturient was returned to the supine position with a left lateral tilt of 15° to facilitate left uterine displacement. The Masimo® pulse oximeter was reconnected to monitor the patient till the end of surgery. Oxygen was given through face mask at 4 L/min.

Ringer's lactate was administered at a rate of 100 ml/10 min. The level of sensory block was checked 5 min after the spinal injection with a cold swab. If a T6 sensory block level was not achieved, these parturients were excluded from the study and managed according to institutional protocol. Maximum cephalad spread was checked 20 min after SAB. NIBP, heart rate (HR), respiratory rate (RR), SpO 2 and PI were recorded at 2 min intervals after the SAB up to 20 min and then at 5 min intervals by the same anaesthesiologist who administered SAB till the end of surgery. Hypotension was defined as a decrease in MAP <65 mm of Hg and treated with IV bolus of 6 mg injection ephedrine and 100 ml of Ringer lactate. The first 60 min following spinal anaesthesia was considered for anaesthesia-induced hypotension. Bradycardia was defined as HR <55 beats/min and treated with injection atropine 0.6 mg IV bolus. Following extraction of the baby, Apgar score was recorded at 1 st and 5 th min. Injection oxytocin 10 units was given as uterotonic following baby extraction at a rate of 200 mU/min as a separate infusion. Patients requiring additional oxytocics and/or additional surgical interventions excluded from the study. The incidence of other side effects such as nausea, vomiting if observed were recorded.

Categorical and discrete data are presented as tables, and continuous data represented by graphs. Discrete and continuous data were analysed for normal distribution using Shapiro–Wilk test. Chi-square test was applied to assess statistical significance for discrete and categorical data. Independent sample t -test and Mann–Whitney U-test were applied for continuous data which showed normal and skewed distribution, respectively. Regression analysis with Spearman's rank correlation coefficient was done to assess the correlation between baseline PI with other parameters. A Receiver Operating Characteristic (ROC) curve was obtained for baseline PI compared with the hypotension episodes of 126 patients. Data were analysed using SPSS (Statistical Package for Social Sciences) version 20. (IBM SPSS Statistics for Windows, version 20.0, IBM Corp., Armonk, NY, USA) P < 0.05 was considered statistically significant.

A total of 126 patients were included in the study. Two parturients were excluded from the study due to an inadequate level of the spinal blockade, and four parturients had to be excluded due to the requirement of additional oxytocics, as the drugs administered could influence the HR and blood pressure of the patients. Fifty-seven patients were in Group I and 63 patients were in Group II for final analysis [ Figure 1 ]. The demographic parameters such as age, weight and height were comparable between the two groups [ Table 1 ]. The average duration of surgery in both groups was comparable (Group I - 45.87 ± 11.14 min and Group II - 47.93 ± 9.78 [ P = 0.2]).

CONSORT Flow Diagram

Comparison of demographic characteristics between two groups

The median level of cephalad spread of sensory block achieved in both groups was T6. (interquartile range [IQR] - T4–T6).

The PI values in both groups on assessment showed skewed distribution and the median PI in Group I was 2.45 (IQR [1.8–2.8]), and in Group II was 5.4 (IQR [4.25–7.1]). The skewed distribution to the right around the PI value of 3.5, was observed when baseline PI values of both groups were combined and assessed for normal distribution.

Intraoperatively, the HR was comparable between the two groups.

The difference between the two groups with respect to systolic blood pressure (SBP), diastolic blood pressure (DBP) and MAP was statistically significant for the first 25 min [ Figure 2 ]. The difference in SBP was most significant during the 2 nd , 4 th , 6 th , 10 th and 15 th min with values being lower in Group II than Group I, whereas difference in DBP was most significant during the 4 th , 10 th , 15 th , 20 th and 25 th min and the difference in MAP was most significant during the 2 nd , 4 th , 6 th , 10 th , 15 th , 20 th and 25 th min. The DBP and MAP were also lower in Group II than Group I.

Comparison of systolic blood pressure, diastolic blood pressure and mean arterial pressure between the two groups intraoperatively. Systolic, diastolic and mean arterial pressure values presented as mean ± standard deviation. Statistical analysis done using independent t -test P > 0.05

The ROC curve yielded 3.85 as a more appropriate cut-off with a well balanced 76% sensitivity and specificity. The area under the ROC curve (AUC) was 0.848 [ Figure 3 ].

ROC curve depicting baseline PI against incidence of hypotension

Area Under the Curve

The incidence of hypotension in Group I was 10.5% (6/57) compared to 71.42% (45/63). This was clinically and statistically highly significant ( P < 0.001, odds ratio –0.07). In Group I, four patients had one episode of hypotension, one patient had two episodes, and one patient had three. In Group II, twenty-four patients had one episode of hypotension, 16 patients had two episodes, four patients had three episodes, and one patient had four episodes [ Table 2 ]. Eighty-nine percent of patients in Group I had no hypotension. Thirty-two percent of patients in Group II had multiple episodes of hypotension ( P < 0.001).

Requirement of ephedrine and intravenous fluids and number of episodes of hypotension

Median ephedrine usage in Group I was 0 mg (IQR 0–0 mg) and 6 mg (IQR 6–12) in Group II ( P < 0.001) The amount of IV fluids required in Group I was also lower than Group II ( P < 0.001) [ Table 2 ]. One patient belonging to Group II developed bradycardia which was treated with injection atropine 0.6 mg IV.

On Spearman's rank correlation we found highly significant correlation between baseline PI >3.5 and number of episodes of hypotension ( r s 0.416, P < 0.001), total dose of ephedrine used ( r s 0.567, P < 0.001) and total IV fluids used ( r s 0.249, P = −0.019).

Post hoc power analysis comparing the incidence of hypotension and vasopressor use between the two groups showed a power of more than 90%, at confidence intervals of 95%. The sensitivity and specificity of baseline PI with a cut-off of 3.5 was 69.84% and 89.29% respectively.

The RR and SpO 2 were comparable between the two groups throughout the study period. There was no significant difference in Apgar scores between the groups at 1 st and 5 th min. The incidence of nausea and vomiting was similar in both groups (Group I – 4/57 (7.01%), Group II 9/63 (14.28%), P = 0.20).

In the present study, the incidence and severity of hypotension, vasopressor requirement was higher in parturients whose baseline PI values were greater than 3.5. The ROC curve revealed that PI discriminated well between patients who developed hypotension versus those who did not; it yielded a new baseline PI value of 3.85 as the cut off point for predicting hypotension in parturients undergoing caesarean section under sub arachnoid block.

Hypotension following administration of spinal anaesthesia for caesarean delivery is common.[ 8 ] There is no definite monitoring system which may predict the likelihood of developing hypotension so that additional precautions may be taken. Studies have tried to evaluate the usefulness of perfusion index in predicting hypotension following spinal anaesthesia in casearean section.[ 7 ]

The principle of SpO 2 is based on two light sources with different wavelengths 660 nm and 940 nm, emitted through cutaneous vascular bed of finger or earlobe.[ 6 ] The absorbance of both wavelengths has a pulsatile component, which represents fluctuations in the volume of arterial blood between the source and the detector. The non-pulsatile component is from connective tissue, bone and venous compartment. The perfusion index (PI) is the ratio of the pulsatile component (arterial) and non-pulsatile component of light reaching the detector.

Healthy pregnancy is characterised by a decrease in systemic vascular resistance, increased total blood volume and cardiac output.[ 9 ] The reduction of systemic vascular resistance may vary in parturients depending on various factors.[ 9 , 10 , 11 , 12 , 13 ] This decrease in tone will correspond to higher perfusion index values due to increase in pulsatile component due to vasodilatation. Induction of a sympathectomy by spinal anaesthesia will cause a further decrease peripheral vascular tone and increase pooling and hypotension. Parturients with high baseline perfusion index are expected to have lower peripheral vascular tone and hence are at higher risk of developing hypotension following spinal anaesthesia. PI has been used in the study by Mowafi et al . to detect intravascular injection of the epinephrine-containing epidural test dose, hence its reliability to detect vasoconstriction has been demonstrated successfully.[ 4 ] Ginosar et al . demonstrated that increase in PI following epidural anaesthesia was a clear and reliable indicator of sympathectomy.[ 5 ]

In contrast, a recent study performed by Yokose et al .[ 14 ] demonstrated that PI had no predictive value for hypotension in parturients undergoing LSCS following SAB. This discrepancy was attributed to various methodological differences, such as the definition of hypotension, co-loading with colloids and method of calculation of baseline PI.

The cut-off value of baseline perfusion index for prediction of hypotension following spinal anaesthesia was chosen as 3.5 based on a study conducted by Toyama et al .[ 7 ] who did regression analysis and ROC curve analysis and concluded that a baseline perfusion index cut-off point of 3.5 could be used to identify parturients at risk for such hypotension. An attempt was made to explore the predictive ability of this value in the Indian population, in this study. Further, only the baseline value was considered for analysis, since we did not try to explore the correlation between changes in serial PI values with the incidence of hypotension.

In this study, the baseline PI >3.5 and probability of hypotension were significantly correlating, a finding similar to study by Toyama et al .

On Spearman rank correlation, a highly significant correlation was found between baseline PI >3.5 and number of episodes of hypotension, the total dose of ephedrine used and total IV fluids used. A higher requirement of vasopressor was seen in parturients with baseline PI >3.5.

Toyama et al . found a sensitivity and specificity of 81% and 86%, respectively, for baseline PI with a cut-off of 3.5 to predict hypotension, whereas in this study, the specificity was comparable, 89.29%, but sensitivity was lower, 69.84%.

In this study, the consumption of IV fluid was higher than that in the study by Toyama et al . As we used injection ephedrine and fluid bolus to treat hypotension while they used only injection phenylephrine to treat hypotension.

Uterotonics such as prostaglandin F2 alpha, methylergometrine are powerful vasoconstrictors and would have influenced the observations and hence patients receiving these drugs were excluded from analysis, as they received these drugs between 20 and 25 min after spinal anaesthesia.

There are many limitations in this study. Patient movement and any stimulus increasing sympathetic activity like anxiety could easily change the PI values. In this study, we recorded baseline PI values with utmost care to avoid patient movement, especially while recording baseline values and all patients were counselled before taking them up for surgery to allay anxiety. The baseline value of PI could have been affected due to aortocaval compression in supine position while recording baseline values. Systemic vascular resistance was not measured, but it would be invasive and unnecessary for the uncomplicated caesarean section. Arterial blood gas analysis for both the mother and foetus was not done which could have ruled out hypoxia resulting from hypoperfusion.

Since PI is dependent on the vascular tone of digital vessels, its role in predicting hypotension in conditions where the tone of these vessels is affected is questionable and more studies regarding its use in other patients needs to be done before it can be accepted as a universal non-invasive tool to predict hypotension following spinal anaesthesia. In addition, further studies comparing PI with invasive and accepted tools of haemodynamic monitoring may throw more light regarding its utility.

Perfusion Index (PI) can be used as a tool for predicting hypotension in healthy parturients undergoing elective caesarean section under SAB. Parturients with baseline PI >3.5 are at higher risk of developing hypotension following SAB compared to those with baseline PI ≤3.5.

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A study to evaluate perfusion index as a predictor of hypotension following spinal anesthesia for caesarean section

Lal, Jatin; Bansal, Teena; Bhardwaj, Shweta; Jain, Mamta; Singh, Anish Kumar

Department of Anaesthesiology and Critical Care, Pt. B. D. Sharma University of Health Sciences, Rohtak, Haryana, India

Address for correspondence: Dr. Teena Bansal, 19/6 J Medical Campus, PGIMS, Rohtak - 124 001, Haryana, India. E-mail: [email protected]

This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 4.0 Unported, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Background and Aims: 

The perfusion index (PI) has been used as a marker of peripheral perfusion. A lower PI indicates greater peripheral vascular tone and increased risk of hypotension following spinal anesthesia. The present study was conducted to evaluate and correlate perfusion index (PI) with incidence of hypotension following spinal anesthesia for caesarean section.

Material and Methods: 

The present prospective, double blind, observational study included sixty full term parturients in the age group 18-35 years belonging to American Society of Anesthesiologists (ASA) physical status I and II, having singleton pregnancy undergoing caesarean section under spinal anesthesia. On the basis of baseline PI, patients were allocated into one of the two groups: Group I (n = 30) Patients with baseline PI ≤.3.5 and Group II (n = 30) Patients with PI >3.5.

Results: 

The incidence of hypotension in group I was 40% as compared to 73.3% in group II (p = 0.009). Thus, the incidence of hypotension in group II with baseline PI >.3.5 was more as compared to group I. Patients in group II with baseline PI >.3.5 had significantly more episodes of hypotension as compared to those in group I with baseline PI ≤3.5.

Conclusion: 

PI can be used as a useful tool for predicting hypotension in parturients undergoing elective caesarean section under spinal anesthesia in everyday practice.

Introduction

Caesarean section is routinely performed under spinal anesthesia that induces sympathetic blockade which leads to decreased vascular resistance resulting in hypotension. This spinal anesthesia induced hypotension is aggravated in pregnant patients because of decreased cardiac output due to blood pooling in blocked areas of the body in addition to decreased vascular resistance due to sympathetic blockade.[ 1 ] The peripheral vascular tone is decreased in parturients at term, especially in those who are multiparous. Although baseline volume status affects the degree of hypotension, baseline peripheral vascular tone may also have an influence on the development of hypotension. As a result of decreased peripheral vascular tone, blood volume gets trapped in the extremities even before spinal anesthesia and the sympathetic blockade with spinal anesthesia further increases the blood pooling. Therefore, parturients who have low baseline vascular tone may be at an increased risk of developing hypotension after spinal anesthesia. As compared to 33% of non-pregnant patients, approximately 70% parturients develop hypotension following spinal anesthesia.[ 2 ]

Severe adverse effects are related to hypotension in mother such as dizziness, nausea, and vomiting and may cause umbilical arterial acidosis in infants. Therefore, it is critically important to identify those who are at risk of hypotension while performing spinal anesthesia in caesarean section, as it would give clinicians an opportunity to take preventative measures such as pre-anesthetic volume expansion and prophylactic vasopressor administration. Non-invasive blood pressure (NIBP) measurement is the standard method of monitoring intraoperative hemodynamics. However, beat to beat variation in perfusion dynamics cannot be measured by this method and limits its efficacy.[ 3 ]

The perfusion index (PI) has been used as a marker of peripheral perfusion. A lower PI indicates greater peripheral vascular tone. Thus PI is a valuable objective during anesthetic practice to find out non-invasive methods for predicting the hemodynamic responses to anesthetic drugs and techniques.[ 4 ] Clinical studies demonstrated that an increase in PI is an early indicator that spinal anesthesia has initiated peripheral vasodilation which typically occurs before the onset of anesthetic effect; however, the literature is limited.[ 5 6 ] Thus, PI can be used as a marker of peripheral perfusion and can be used to assess peripheral perfusion dynamics due to changes in peripheral vascular tone and to detect the likelihood of development of hypotension following spinal anesthesia. Hence, the present study was conducted to evaluate and correlate PI with incidence of hypotension following spinal anesthesia for caesarean section.

Material and Methods

The present prospective, double blind, observational study was conducted in the department of Anaesthesiology and Critical Care, PGIMS Rohtak. Approval for the study was obtained from Institutional Ethics Committee and the trial was registered (CTRI/2019/03/018058). Sixty full term parturients in the age group 18-35 years belonging to American Society of Anesthesiologists (ASA) physical status I and II, having singleton pregnancy undergoing caesarean section with pfannenstiel incision under spinal anesthesia were included in the study. Informed written consent was taken. Parturients with contraindications to spinal anesthesia, known risk factor for postpartum hemorrhage, significant obstetric disease such as pregnancy induced hypertension or preeclampsia, cardiovascular or cerebrovascular disease, morbid obesity with a BMI >40 kg m -2 and gestational age <36 or >41 weeks were excluded from the study.

All patients were subjected to complete general physical and systemic examination. Investigations like hemoglobin, bleeding time, clotting time, and urine examination were carried out in all the patients. The purpose and protocol of the study was explained to the patients and informed written consent was obtained. Patients were kept fasting for 8 hours prior to the scheduled time of surgery. They were premedicated with oral ranitidine 150 mg night before and with metoclopramide 10 mg and ranitidine 150 mg two hours prior to surgery with sips of water.

Upon arrival in the operating room, all patients were laid supine with wedge under right flank to achieve leftward tilt of 150. Routine monitoring including heart rate, electrocardiogram, NIBP and SpO 2 was started. Peripheral venous access was secured with 18G cannula and baseline hemoglobin was taken. All patients were preloaded with 10 mL kg -1 of Ringer Lactate solution over 10 minutes before spinal anesthesia. Base line systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial blood pressure (MAP), heart rate (HR) and SpO 2 were recorded. Baseline perfusion index was measured by an anesthesiologist who was not involved in the further intraoperative monitoring of the patient, using a specific pulse oximeter probe (Masimo Radical 7 R ; Masimo Corp., Irvine, CA) which was attached to left index finger of all patients to ensure uniformity.

On the basis of baseline PI, patients were allocated into one of the two groups: Group I (n = 30) Patients with baseline PI ≤3.5 and Group II (n = 30) Patients with PI >3.5. A standard anesthesia protocol was followed. All patients were given spinal anesthesia in sitting position at L3-L4 or L4-L5 interspace with 25 G Quincke’s spinal needle. After free flow of cerebrospinal fluid, 10 mg of 0.5% hyperbaric bupivacaine was administered without barbotage. Patients were immediately placed in supine position with 150 left lateral tilt. Oxygen was delivered to all patients via face mask at the rate of 4 Lmin -1 . Intravenous Ringer Lactate was infused at constant rate of 15 mLkg -1 hr -1 till the end of surgery.

Sensory block height level was checked by assessing the perception of coldness using spirit swab at 2 minutes interval till 10 minutes and thereafter at 5 minutes interval till 20 minutes. At the same point of time, motor blockade was assessed using modified Bromage scale. Surgery was allowed to commence as soon as T6 dermatome was anesthetized. After delivery of fetus and clamping of umbilical cord, oxytocin infusion was started (20 U of oxytocin in 500 ml of 0.9% normal saline at the rate of 250 mlhr -1 ). Hypotension, defined as decrease in systolic blood pressure by more than 20% from baseline or less than 80 mm Hg was treated with boluses of 6 mg intravenous ephedrine and 100 ml Ringer Lactate. Bradycardia, defined as HR less than 60 beats per min (bpm) was treated with boluses of 0.6 mg IV atropine.

A second anesthesiologist who was blinded to the group allocation recorded demographic data (age, height, weight, body mass index), hemodynamic variables (SBP, DBP, MAP, HR, SpO 2, and PI) and need for atropine and ephedrine. Hemodynamic variables were noted at 2 min interval after spinal injection for the first 20 minutes and then at 5 minutes interval for further 50 minutes and then at the end of surgery. Following completion of the study the data was collected and subjected to statistical analysis.

Duggappa et al . found incidence of hypotension in group I (PI <3.5) to be 15% and in group II (PI >3.5) to be 65%[ 5 ] Based on this study and taking a error of 5% and 1-b power to be 95% we enrolled 60 cases, allocated in two groups of 30 each. The data were coded and entered into Microsoft Excel spreadsheet. Analysis was done using SPSS version 20 (IBM SPSS Statistics Inc., Chicago, Illinois, USA) Windows software program. Chi square test for categorical data and student t-test for continuous data were used. Quantitative variables are expressed as mean ± SD and compared between groups using unpaired t-test. Level of significance was set at P ≤ 0.05.

The two groups were comparable with respect to age, weight, height, and BMI. The mean age of patients in group I was 25.23 ± 2.69 years and in group II was 26 ± 2.94 years (p = 0.148). The mean weight of patients in group I was 65.23 ± 4.61 kg and in group II was 66.47 ± 5.4 kg (p = 0.148). Mean height of patients in group I was 155.37 ± 3.37 cm and in group II was 156.60 ± 3.82 cm (p = 0.095). The mean BMI of patients in group I was 27.07 ± 2.42 kgm -2 and in group II was 27.64 ± 2.13 kgm -2 (p = 0.459).

The baseline PI in group I was 1.79 ± 0.96 and in group II was 5.85 ± 1.46. the difference in PI at various interval was significant in both the groups (p < 0.05) [ Table 1 ]. Mean baseline SBP in group I was 124 ± 9.27 mmHg and in group II was 117.93 ± 8.58 mmHg (p = 0.002). Thus the patients in group II (PI > 3.5) had significant lower mean baseline SBP as compared to group II. The mean baseline DBP in group I was 79.73 ± 7.59 mmHg while in group II was 74.50 ± 5.4 mmHg (p = 0.002). The mean baseline MAP in group I at baseline was 95.77 ± 8.07 mmHg and in group II was 89.90 ± 5.44 mmHg (p < 0.001).

The incidence of hypotension in group I was 40% as compared to 73.3% in group II (p = 0.009) [ Table 2 ]. Thus, the incidence of hypotension in group II with baseline PI > 3.5 was more as compared to group I. In group I, 18 patients (60%) did not have any episode of hypotension, 4 patients (13.3%) had 1 episode and 8 (26.6%) patients had multiple episodes. In group II, 8 patients (26.7%) did not have any episode of hypotension, 5 patients (16.7%) had 1 episode and 17 (56.6%) patients had multiple episodes of hypotension. When compared statistically using Chi square test, there was significant difference in the two groups with respect to number of episodes of hypotension (p value = 0.006) [ Table 3 ]. Thus, the patients in group II with baseline PI >3.5 had significantly more episodes of hypotension as compared to those in group I with baseline PI ≤3.5.

The mean bolus of ephedrine required in group I was 2.00 ± 0.82 whereas in group II, it was 3.05 ± 1.33 (p = 0.03). The mean dose of ephedrine used in group I was 12.00 ± 4.90 mg whereas in group II, it was 18.27 ± 7.96 mg (p = 0.030). Thus, the dose of ephedrine required was more in group II as compared to group I. The mean fluid consumption in group I was 1331.67 ± 332.05 ml and in group II was 1630.00 ± 289.05 ml (p < 0.001). The fluid consumption in group II was significantly more as compared to group I.

Hypotension following spinal anesthesia results due to blockade of pre-ganglionic sympathetic fibers and due to blood pooling in blocked areas of body. Changes in peripheral circulation are seen in normal pregnancy viz decreased peripheral vascular resistance, arterial, and venous vasodilation and increased intravascular volume. These changes further have an influence on degree of hypotension which occurs after spinal anesthesia.[ 7 ] Hypotension may have severe adverse effects on maternal and fetal morbidity and vasopressors are required in up to 80% of patients to treat it.[ 8 ]

Many hemodynamic parameters have been studied as predictors of hypotension but none of the monitoring system can definitely predict the likelihood of hypotension.[ 3 9 ] PI is a non-invasive and continuous method for assessing the peripheral tissue perfusion by calculating the ratio of pulsatile (arterial component) and non-pulsatile components (venous, capillary, and other tissues) of light reaching the pulse oximeter detector.[ 10 ] The median (IQR) of baseline PI was 1.8 (1-2.7) in group I and 5.6 (5.07-6.4) in group II. The skewed distribution to the right around P value of 3.5 was observed when baseline PI values of both groups were combined and assessed for normal distribution. The results of present study are consistent with a study conducted in which authors found that median PI in group 1 was 2.45 (1.8-2.8) and in group 2 was 5.4 (4.25-7.1).[ 5 ]

The incidence of hypotension in group I with baseline PI ≤3.5 was 40% (12/30) as compared to 73.3% (22/30) in group II. The incidence of hypotension in group II with baseline PI was significantly more as compared to group I (p = 0.009) [ Table 2 ]. The present study results are consistent with the various studies. Toyama et al . found that hypotension occurred in 82% of patients (17/19) with high baseline PI whereas hypotension was observed in 25% patients (4/16) with low baseline PI. They also found a significant correlation between baseline PI and degree of decrease in SBP from baseline after SA.[ 11 ] Dugappa et al . also found that the incidence of hypotension was 10.5% (6/57) in patients with baseline PI ≤3.5 and 71.42% (45/63) in patients with baseline PI >3.5 which was clinically and statistically highly significant (p < 0.001).[ 5 ] Varghese RV found that the incidence of hypotension in group 1 (PI >3.5) was 86.67% whereas in group 2 (PI ≤3.5) was 6.67% which was highly significant (p < 0.05).[ 6 ] George et al . found that the incidence of hypotension was 66.7% among the study subjects and they concluded that the incidence and severity of hypotension was higher in parturients with baseline PI >3.6.[ 12 ]

There was a positive correlation of baseline PI with number of episodes of hypotension (r = 0.109, P = 0.01) in group II while there was no correlation between baseline PI and number of episodes of hypotension in group I (r = -0.236 P = 0.210). The results of present study are similar to different studies. In the study conducted by Dugappa et al. , among the patients with baseline PI < 3.5, 4 patients had 1 episode, 1 patient had 2 episodes and 1 patient had 3 episodes. While in patients with PI > 3.5, 24 patients had 1 episode, 16 patients had 2 episodes, 4 patients had 3 episodes and 1 patient had 4 episodes. They also found that the number of episodes of hypotension were more in group with high baseline PI (p < 0.001). A significant correlation between PI > 3.5 and number of episodes of hypotension was found (r s 0.416 P < 0.001).[ 5 ] Varghese RV found that in patients with PI > 3.5, 11 patients had 1 episode, 12 patients had 2 episodes and 3 patients had 3 episodes of hypotension. In patients with PI < 3.5, 93% patients did not have hypotension. 1 pregnant woman had 1 episode and 1 had 2 episodes of hypotension. A significant difference was found in the number of episodes of hypotension between both groups (p = 0.000).[ 6 ]

The ROC curve yielded 73.3% sensitivity and 76.67% specificity (AUC = 0.74 P = 0.03). The ROC curve revealed that PI discriminated well between patients who developed hypotension versus those who did not develop hypotension [ Table 4 and Figure 1 ]. The present study results are consistent with various studies. Toyama et al . found the baseline cut-off point for PI that predicted hypotension as 3.5 with a sensitivity of 81%, specificity of 86%, a positive predictive value of 89% and negative predictive value of 75% based on ROC analysis (AUC = 0.866 P = 0.0003).[ 11 ] Dugappa et al . found the optimal cut-off of PI for predicting hypotension as 3.5 with sensitivity of 69.84% and specificity of 89.29% base on ROC analysis (AUC = 0.848 P=<0.001).[ 5 ] Varghese RV found that the ROC curve yielded 3.83 as an appropriate cut-off value to predict hypotension with sensitivity and specificity of 86.7% and 93.33% respectively with positive predictive value of 92.86% and negative predictive value of 87.5%.[ 6 ] George et al . also found that PI discriminated well between patients who developed hypotension versus those who did not. They found a cut-off value of 3.6 to predict hypotension with sensitivity 80% and specificity 40%.[ 12 ]

Limitations

There are several limitations in present study. Photoplethysmographic analysis is sensitive to patient movement and PI is also affected by several factors like stress and anxiety that can lead to sympathetic activation which leads to peripheral vasoconstriction leading to decrease in PI. In the present study, the baseline PI was recorded with utmost care to avoid patient movement and readings were recorded after stabilizing the patient. Patient temperature at monitoring site can also affect the PI values. PI can also be affected by systemic vascular resistance but since its measurement is invasive and unnecessary in uncomplicated CS, it was not recorded.

In conclusion, the present study demonstrated that parturients with baseline PI >3.5 measured at the finger are at higher risk of developing hypotension during spinal anesthesia for caesarean section compared to those with baseline PI ≤3.5. Hence the baseline PI cut-off point of 3.5 can be used to identify parturients at risk for such hypotension. Thus, PI can be used as a useful tool for predicting hypotension in parturients undergoing elective caesarean section under spinal anesthesia in everyday practice.

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Pulse-oximetry Derived Perfusion Index as a Predictor of the Efficacy of Rescue Analgesia After Major Abdominal Surgeries

E-mail address of dr. ashraf nabil saleh.

[email protected]

E-Mail Address of Dr. Raham Hasan Mostafa

E-mail address of dr. ahmad nabil hamdy, e-mail address of dr. amr fouad hafez, downloads 11,803.

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Study Objective:

The use of an easy to apply reliable tool is essential to assess pain in patients in intensive care units. This study aimed primarily to evaluate perfusion index usefulness as an objective indicator of pain.

Methods and Measurements:

Data were collected from 40 non-intubated adult patients admitted to the surgical intensive care unit postoperatively. The Masimo pulse co-oximetry perfusion index (PI) probe was attached to the patient. At the time of the first request for analgesia (T1), the Behavioural pain scale non-intubated scoring system (BPS-NI) was recorded with the PI and patients' haemodynamics following which rescue analgesia was given. Thirty minutes thereafter (T2), second measurements for the mentioned parameters were taken.

Main Results:

There was a statistically significant reduction in the BPS-NI score, blood pressure and heart rate after analgesic administration (P-values, <0.001, 0.039 and 0.001, respectively), together with a significant increase in the PI (P-value, 0.004). This means that the PI increases with adequate relief from pain, as indicated by a decrease in BPS-NI score and haemodynamics, but the correlation was not statistically significant between their changes.

Conclusion:

There was no statistically significant correlation between the PI and the pain score or other clinical indicators of pain either before or after the administration of analgesic.

1. INTRODUCTION

In the Intensive care unit (ICU), pain is usually underestimated due to the difficulty of its assessment in critically ill patients. It can evolve from many sources, for e.g. , postoperative surgical incisions, penetrating chest tubes, and even ICU procedures as bedside debridement. It was shown that alleviating pain effectively in both intubated and non-intubated ICU patients has been associated with improved outcomes [ 1 ]. Scales such as the Visual analogue scale (VAS) and numeric rating scale (NRS) are used to assess pain intensity postoperatively. In order to use these scales, patients need to be able to understand what is said to them and express themselves. But this cannot be carried out for individuals with communication problems [ 2 ]. Also, the use of haemodynamic changes has been demonstrated to be neither valid nor reliable as it is affected by many other aetiologies, and guidelines recommend that vital signs should not be used to evaluate pain in ICU patients [ 3 ]. This phenomenon has led to the construction of categorical and numerical methods of pain assessment in critically ill patients. The behavioural pain scale (BPS) -whether intubated or non-intubated forms- has been reported as a valid and reliable tool for pain assessment in ICU patients with recommendations of its use to assess the presence of pain in adult ICU patients when self-reporting is not possible [ 4 ]. But unfortunately, the use of Behavioural pain scale non-intubated scoring system (BPS-NI) scale requires sustained efforts to educate and train the ICU team regarding the scale because of its subjective nature [ 5 ]. Also, BPS-NI is time-consuming with multiple points of assessment, making it non-practical [ 6 ]. The need for simple, non-invasive, rapid, and objective tools for pain evaluation represents a present gap in the literature. The Masimo device could be a promising indirect tool for pain assessment. The Masimo set pulse oximetry system can measure the perfusion index (PI) at the monitored site by calculating the relation between pulsatile and static blood in peripheral tissues. In contrast to the conventional pulse oximeter which measures O2 saturation, Masimo Signal Extraction Technology depends upon the amount of blood at the monitoring site, not upon blood oxygenation. Therefore, PI is considered as an indirect, non-invasive, and continuous measure of peripheral perfusion. It ranges from 0.02% (very weak pulse strength) to 20% (very strong pulse strength) [ 7 ]. Pain induces vasoconstriction due to sympathetic nervous system stimulation with a subsequent decrease in PI [ 8 ]. This direct relation between pain and sympathetic stimulation raises the hypothesis that the PI can be used as an indirect objective tool for pain assessment. The current study aimed primarily to evaluate the correlation between perfusion index and other clinical indicators of pain after rescue analgesia administration and so detecting its usefulness as an objective indicator of pain assessment in ICU.

2. METHODS AND MEASUREMENTS

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The work was approved by the Ethics committee of Ain Shams University hospital (FMASU R 05/ 2019) on 23/1/2019. The study was prospectively registered with Pan African Clinical Trial Registry (PACTR) with Registration Number PACTR201901839969911 in accordance with WHO and ICMJE standards. Written informed consent was obtained from all subjects or their legal surrogate.

This is a prospective observational study that was conducted in Ain Shams university hospital intensive care unit through the period from January 2019 to October 2019. The study comprised 40 patients. Eligibility criteria for this study included patients with American Society of Anaesthesiologists (ASA) physical status I to III, of either sex, 18-80 years of age, non-sedated non-intubated patients that were admitted postoperatively to ICU after major abdominal surgery. We categorized the participants into two “age groups” according to age: an elderly group (> 60 years) and a young group (< 60 years). Then we further classified each “age group” into a male group and a female group. Now we had a total of 4 groups: an elderly male group (> 60 years) = OM group, an elderly female group (> 60 years) = OF group, a young male group (< 60 years) = YM group and a young female group (< 60 years) = YF group. Exclusion criteria involved patients with fever, hypothermia, history of a neurological, psychiatric, dementia or chronic pain disorder. Patients with unstable haemodynamic status and unconscious patients were also excluded. Patients who had combined general epidural anaesthesia or Transversus abdominis plane block were also excluded.

2.1. Patients’ Postoperative Interventions and Management

After extubation and full recovery, patients were admitted to ICU. Standard monitors were applied: an Electrocardiogram, pulse oximeter, and non-invasive arterial blood pressure monitor, and all baseline readings were recorded. All patients received nasal oxygen (4 L/min). The oximeter probe (Radical-7 ® , Masimo Corporation, Irvine, CA, USA) used to monitor the PI was attached to the middle fingertip of the hand and was wrapped in a towel to decrease heat loss. The patients were kept warm with wool blankets, warm i.v. fluids, and a warm air-forced device. All patients were observed until they asked for rescue analgesia. Sedation was assessed by Richmond agitation-sedation scale score (RASS) that was recorded at specific timings: on arrival to ICU, and after 1 and 2 hours from arrival to ICU [ 9 ]. The RASS is a 10- point validated sedation scale with 4 levels for agitation, 5 levels for sedation, and 1 level for calm, awake patients. The scale’s anchor is centered at 0 (alert and calm) [ 9 ]. Our intensive care unit analgesia protocol in general is 1 g i.v. paracetamol repeated every 6 h and 5 mg Nalbuphine increments upon patients’ request or if Behavioural pain scale non-intubated scoring system (BPS-NI) ≥ to 5, to whatever 1 st occurred. Pain assessment in this study was achieved by Behavioural pain scale non-intubated scoring system [ 6 ]. The BPS-NI evaluates three behavioural domains ( i.e. , facial expression, movements of upper limbs and vocalization). Each domain contains four descriptors that are rated on a 1–4 scale, and the total BPS value can range from 3 (no pain) to 12 (most pain). The procedure for using the BPS is estimated to take minimal time (2–5 minutes). Because each domain of the BPS-NI contains four descriptors, it has the advantage of avoiding a possible observer bias that is described as when an observer rates preferentially the middle item of a three-point scale [ 6 ]. At the time of the first request for analgesia (T1), Behavioural pain scale non-intubated scoring system (BPS-NI) was recorded together with the PI, heart rate (HR), mean arterial blood pressure (MAP), peripheral oxygen saturation, and axillary temperature, following which 5 mg Nalbuphine and 1 gram paracetamol were given. Thirty minutes after postoperative analgesia (T2), second measurements for the mentioned parameters were taken. We considered the following criteria as indicators of pain relief: a 100% increase of PI value from baseline.

2.2. Data Collection

The required sample size was calculated using the G*Power software v. 3.1.9.4 [ 10 ]. The primary outcome measure was the correlation between the change in PI and the change in pain score as assessed using the BPS-NI. We considered that a correlation coefficient of 0.45 would be of clinical value. So, assuming an alpha error of 0.05, we calculated that a sample size of 40 patients would be required to achieve a power of 85% to detect statistical significance for a correlation coefficient of 0.45 between the change in PI and change in pain score. Data were analysed using IBM© SPSS© Statistics version 23 (IBM© Corp., Armonk, NY). Categorical variables were presented as number and percentage. Normally distributed numerical variables were presented as mean and standard deviation and intergroup differences were compared using the unpaired t-test. The paired t-test was used to compare normally distributed paired data. Non-normally distributed numerical variables were presented as median and interquartile range and intergroup differences were compared using the Mann-Whitney U-test. The Wilcoxon signed ranks test was used to compare non-normally distributed paired data. Correlations were tested using the Spearman rank correlation. Multivariable linear regression was used to examine the effect of age or sex on the change in PI after analgesic administration. The PI was subjected to logarithmic transformation prior to entry into regression because of marked skewness of its frequency distribution. Two-sided P-values <0.05 were considered statistically significant.

We studied 40 age-matched patients, 20 males and 20 females, with a mean ± SD age of 48 ± 19 years. The characteristics of the study population and operative details are shown in Table 1 .

Table 2 shows a comparison of pain score, PI and other indicators of pain before and after analgesic administration. There was a statistically significant reduction in the BPS-NI score, MAP and heart rate after analgesic administration (P-values, <0.001, 0.039 and 0.001, respectively). On the other hand, there was a statistically significant increase in the PI after analgesic administration (P-value, 0.004). Regarding the difference in axillary temperature, there was no statistically significant difference between the measured axillary temperature at T1 and that at T2 (P-value, 0.442). There was no statistically significant correlation between the PI and the pain score or other clinical indicators of pain either before or after administration of analgesic. There was no statistically significant correlation between the change in PI and the change in pain score or other clinical indicators of pain (Table 3 ). Studying the correlation of PI with other clinical variables before and after administration of analgesic showed a weak inverse correlation between the PI after administration of analgesic and the RASS score at 1 h (rho, -0.378; P-value, 0.016) and moderate inverse correlation between the change in PI and the RASS score at 1 h (rho, -0.409; P-value, 0.009). There was no statistically significant relationship between the age or sex and the PI either before or after the administration of analgesic. Neither there was a statistically significant relationship between the change in PI and the age or sex (Table 4 ).

Table 5 shows the results of multivariable regression analysis for the effect of age or sex on the change in PI (Δ PI) with adjustment for other confounding factors. After adjustment for the effect of American Society of Anaesthesiologists - Physical Status, operative time and intraoperative opioid consumption, there was no statistically significant relationship between the change in PI and the patient’s age (P-value, 0.269) and sex (P-value, 0.482).

4. DISCUSSION

In our study, there was a statistically significant increase in the PI after analgesic administration. Also, there was a statistically significant reduction in the BPS-NI score, MAP and heart rate after analgesic administration. But, we did not find any statistically significant correlation between the absolute value of “PI and other examined clinical pain indicators (the BPS-NI, MAP, and HR)” before or after rescue analgesia administration as well as with their changes. The relationship between analgesia and PI is the basis of our hypothesis in this study. The PI is a non-invasive and easy method that can be used for evaluating pain and monitoring the effectiveness of analgesia. It can also eliminate psychological factors such as fear, anxiety, depression, and anger [ 11 ]. This benefit can be more valid in patients suffering from cognitive impairment and dementia especially because common pain behaviour scales are very difficult, require training of the ICU staff and are time-consuming [ 11 ]. There are multiple studies exploring the relationship between PI and pain, whether in awake patients [ 12 , 13 ] or those under general anaesthesia [ 8 ]. And they all proved that PI decreased due to painful stimulus. On the other hand, other studies explored the relationship between PI and analgesia whether under general anaesthesia [ 2 , 11 , 14 ] or epidural analgesia [ 15 ] or transforaminal block [ 16 ]. And they all proved that PI increased after analgesic administration. All of these studies explored different types of pain as postoperative surgical pain [ 2 , 11 , 14 , 15 ], intensive care procedural pain [ 13 ], electric stimulation pain [ 8 , 12 ] and finally, chronic radicular pain [ 16 ].

In agreement with the current study, Tapar and colleagues [ 2 ] showed that there was a statistically significant difference between pre-analgesic and post-analgesic PI, VAS scores and haemodynamics with no correlation between PI absolute values & VAS scores absolute values at pre- and post-analgesic measurements. Also, there was a detected weak negative correlation between the change in PI and the change of pain score (VAS score). It was a prospective observational study that was done on 89 patients that had undergone minor to moderate surgical procedures and were observed in Post Anesthesia Care Unit (PACU) postoperatively. They used morphine increments for post-operative analgesia and the subjective pain score used was VAS score. Another study confirming our findings was carried out by Mohammed and colleagues [ 11 ], in which a Masimo pulse co-oximetry perfusion index was attached to 70 American Society of Anaesthesiologists-Physical Status I adult patients at PACU, who underwent lumbar spine discectomy. The PI was significantly higher at post-analgesic timing than at pre-analgesic timing. This increase was associated with a statistically significant decrease in other measured parameters. This means that the PI increases with adequate relief from pain, as indicated by a decrease in VAS, HR, and MAP. A decrease in VAS was associated with an increase in PI, but the correlation was not statistically significant. Also, the correlation between change in PI and change in VAS score & change in MAP was not statistically significant and this is consistent with our study. It is to be noted that there was a statistically significant negative correlation between change in HR and change in PI. For all patients, analgesia was achieved with i.v. morphine and i.v. 1 g paracetamol and subjective pain scale used was the VAS score. In correspondence to the current study, Nishimura and colleagues [ 12 ] studied the changes in perfusion index in response to noxious electrical stimulation in awake healthy subjects. They measured the PI and pulse rate in 70 healthy volunteers exposed to increasing electrical stimulation until they reached their pain tolerance threshold. They observed a significantly decreased PI in response to electrical stimulation but with no increase in the pulse rate due to its very small intensity. They concluded that the PI may be an independent parameter reflecting the perception of noxious stimuli and offers a non-invasive option for objectively evaluating pain perception. Finally, in a study done by Hasanin and colleagues [ 13 ], they reported a difference between PI values, Systolic blood pressure, Diastolic blood pressure, HR, and pain intensity before and after the pain created by positioning in ICU patients. BPS-NI has been used for subjective pain assessment especially as all patients were sedated (but not-intubated), which might affect their communication with the medical staff. There was a significant increase in the Systolic blood pressure, Diastolic blood pressure, heart rate and BPS-NI post-positioning values compared with pre-positioning values. Also, a significant decrease in PI was also observed at post-positioning values compared with pre-positioning values. Also, no correlation was found between the PI values and any other variable (Systolic blood pressure, Diastolic blood pressure, HR, and BPS-NI) before or after the patient positioning. Hasanin’s study differs from the current study in that the change in BPS-NI showed a good correlation with the change in PI. On the other hand, there are two studies which showed a weak correlation between different parameters. In a retrospective observational study done by Chu and colleagues [ 14 ], the correlation between the PI and VAS score together with their delta change and their percentage change showed weak correlations. They enrolled 80 female patients postoperatively, with a different age range, who were observed in PACU before and after intravenous morphine analgesic administration. The second study was done by Kupeli & Kulhan [ 15 ]. They investigated the relationship between labour pain level and PI in 30 women undergoing spontaneous vaginal delivery under epidural analgesia. They noticed that upon activation of the epidural blockade with 10 mL 0.25% bupivacaine, the PI increased. Also, they noticed a gradual decrease in PI with a fade of epidural analgesia (manifested by a gradual increase in labor pain). They concluded that PI could offer a non-invasive option to objectively assess pain perception and this is in accordance with our study findings. But in opposition, there was a significant negative association between PI and VAS absolute values at the 10th, 30th, 60th minutes and 2nd hour after epidural blockade activation. Also, there was a significant negative association between PI and HR absolute values before the procedure and at the time of administration of epidural analgesia and 5 minutes later. They noted that perfusion index had no significant correlation with both systolic and diastolic blood pressures.

Few studies had explored the effect of age or sex on the change in PI after analgesic administration or painful stimulation. In the current study, there was no statistically significant relationship between the age or sex and the PI either before or after the administration of analgesic. Neither was there a statistically significant relationship between the change in PI and the age or sex. Supporting our findings, Chu and colleagues [ 14 ] stated the same findings in their study. On the other hand, Nishimura and colleagues [ 12 ] observed that the old women group did not show any changes in PI before or after electrical stimulation when compared to other age and sex groups that showed a decrease in PI.

5. LIMITATION

PI measurements are very sensitive to patients’ movements. The rapid fluctuation and sensitivity of PI are its weakness as well as strength in the clinical field. To compensate for this limitation, PI monitoring should be done after ensuring position stability.

Perfusion index can be added to other indicators of pain assessment in ICU. It is easy, non-invasive, free of subjective interpretation, less time-consuming and finally, not affected by age or sex related factors.

ETHICS APPROVAL AND CONSENT TO PARTICIPATE

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The work was approved by the Ethics committee of Ain Shams University hospital (FMASU R 05/ 2019) on 23/1/2019. The study was prospectively registered with Pan African Clinical Trial Registry (PACTR) with Registration Number PACTR201901839969911 in accordance with WHO and ICMJE standards.

HUMAN AND ANIMAL RIGHTS

No Animals were used in this research. All human research procedures followed were in accordance with the ethical standards of the committee responsible for human experimentation (institutional and national), and with the Helsinki Declaration of 1975, as revised in 2013.

CONSENT FOR PUBLICATION

Written informed consent was obtained from all subjects or their legal surrogate.

AVAILABILITY OF DATA AND MATERIAL

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

CONFLICT OF INTEREST

The authors declare no conflict of interest, financial or otherwise.

ACKNOWLEDGEMENTS

We have no affiliations with or involvement in any organization or entity that we may have any financial interests with.

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Open-Access License: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode . This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Address correspondence to this author at the Department of Anaesthesia, Intensive Care and Pain Management, Ain Shams University, El-hay El-Sabee, Nasr City, Cairo, Egypt; Tel: 002/01222530020; E-mail: [email protected]

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BORIS Theses

Evaluation of the clinical assessment of peripheral perfusion by capillary refill time and peripheral perfusion index.

Vestner, Manuel Luca (2020). Evaluation of the clinical assessment of peripheral perfusion by capillary refill time and peripheral perfusion index. (Thesis). Universität Bern, Bern

Background: Impaired peripheral perfusion is among the first manifestations of shock and the last to restore in the critically ill patient. In acute circulatory failure the activation of the sympathetic nervous system leads to a redistribution of blood from non-vital organs to the core in order to conserve oxygen delivery and tissue function of vital organs. Therefore, the clinical assessment of peripheral perfusion is an early and easily applicable parameter for detecting and evaluating tissue hypoperfusion and can help guiding therapy in acute circulatory failure. The peripheral perfusion index (PPI) is a simple, non-invasive tool to assess peripheral perfusion by calculating a quotient of pulsatile versus non-pulsatile blood flow of distal extremities using simple commercial pulse-oximetry, with lower values indicating poorer perfusion. Objectives: With this study we aim to establish the peripheral perfusion index as a non-invasive, objective and continuous measurement comparable to other clinical assessments of peripheral perfusion such as capillary refill time (CRT), mottling score and temperature gradient from core and knee to toe. Furthermore, we aim to establish the relationship between PPI and urine production, arterial lactate concentration and perfusion of solid organs measured by ultrasound. Methods: In this prospective cohort study at a tertiary teaching hospital we analyzed repeated measurements of peripheral perfusion, urine and lactate in 59 critically ill patients admitted to the ICU after cardiac surgery or in septic shock during the first 72 hours after admission, as well as sonographic assessment of organ perfusion in septic patients. Additionally, we established normal values of PPI in 30 healthy volunteers at ambient temperature and at vasoconstriction state by cooling of the upper extremities. Results: In healthy volunteers, patients after cardiac surgery and in septic shock patients, PPI was 4.07 (3.36-4.79), 0.88 (0.66-1.88) and 1.29 (0.86-1.80), respectively and CRT 1.28s (0.96-2.02), 5.32s (4.41-6.23) and 4.07s (3.15-7.28), respectively for initial values in patients and during cooling state in healthy volunteers (median, IQR, all p< 0.001 between volunteers and patients and p=0.42 for PPI and p=0.63 for CRT between patient groups). Cooling in volunteers reduced PPI but did not change CRT (p<0.001, p=0.190). Correlation coefficients between PPI and CRT were -0.44, -0.32 and -0.19, respectively in the three groups (all p<0.003), with better correlation initially r=-0.59/-0.37/-0.34 and -0.54/-0.29/-0.26 for correlation of PPI and CRT in cardiac and septic shock patients (initial measurement/first 10h/first 24h, all p<0.003). However, concordance for changes was low (51% and 46% of CRT and PPI measurements changed in the same direction towards improvement or impairment in cardiac and septic patients). PPI correlated best with temperature gradient (r=-0.47, r=-0.13, both p<0.001). Correlation coefficients between PPI and lactate were -0.31 and -0.13 (both p<0.013), and in septic shock patients (n=17) between PPI and resistive index of right kidney r=0.51, and left kidney r=0.45 (both p<0.037). Conclusions: While in healthy volunteers with artificially induced vasoconstriction PPI correlated well with clinical assessment of peripheral perfusion, the agreement between PPI and CRT, mottling score, temperature gradient, urine, lactate and abdominal organ perfusion measured by ultrasound was low in cardiac surgery and in septic shock patients. Correlation between PPI and CRT was better during the initial period of most impaired peripheral perfusion. The results encourage further investigation of PPI as automated assessment of peripheral perfusion in critically ill patients with acutely impaired hemodynamic function.

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Open Access

Peer-reviewed

Research Article

An observational study: The utility of perfusion index as a discharge criterion for pain assessment in the postanesthesia care unit

Roles Data curation, Formal analysis, Methodology, Writing – original draft

Affiliations Institute of Biomedical Engineering National Taiwan University, Taipei, Taiwan, Department of Anesthesiology, National Taiwan University Hospital Yun-Lin Branch, Yun-Lin, Taiwan

Roles Conceptualization, Supervision, Writing – review & editing

Affiliation Institute of Biomedical Engineering National Taiwan University, Taipei, Taiwan

Roles Data curation, Resources

Roles Conceptualization, Supervision

Affiliation Department of Cardiology, National Taiwan University Hospital, Taipei, Taiwan

Roles Conceptualization, Data curation, Writing – review & editing

* E-mail: [email protected]

Affiliation Department of Anesthesiology, National Taiwan University Hospital, Taipei, Taiwan

• Chun-Lin Chu, 
• Yi-You Huang, 
• Ying-Hou Chen, 
• Ling-Ping Lai, 
• Huei-Ming Yeh

• Published: May 16, 2018
• https://doi.org/10.1371/journal.pone.0197630
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Acute post-operative pain can remain untreated if patients cannot express themselves. The perfusion index (PI) may decrease when pain activates sympathetic tone and may increase after analgesics are administered. We evaluated if the perfusion index is a feasible indicator for objectively assessing pain relief in the postanesthesia care unit (PACU) and calculated the changes in PI measurements at the time of discharge from the PACU relative to baseline PI measurements to examine if the PI is a useful criterion for discharging patients from the postanesthesia care unit. This retrospective observational study enrolled female patients who were admitted for gynecological or general surgery. The patients received general anesthesia and were admitted to the postanesthesia care unit. The PI, visual analogue scale (VAS) score, heart rate, and blood pressure were recorded before and after administration of intravenous morphine. Changes in these parameters before and after analgesics were administered and the difference of these parameters between age and BMI subgroups were compared. The correlation between the PI and VAS score, ΔPI and ΔVAS, and %ΔPI and %ΔVAS were also evaluated. The percentage change in ΔPI (P9-T0/T0) of the patients at the time of discharge from the postanesthesia care unit relative to baseline PI measurements was calculated. Eighty patients were enrolled, and there were 123 instances during which analgesia was required. Heart rate, PI, and VAS score were significantly different before and after analgesics were administered (p < 0.0001). The difference of parameters between age and BMI subgroups were not significant. The correlation between the PI and VAS score, ΔPI and ΔVAS, and the percentage change in ΔPI and ΔVAS showed weak correlations in age, BMI subgroups, and all measurements. The baseline PI and the PI when arriving at and when being discharged from the postanesthesia care unit were significantly different (p < 0.01). The mean percentage change in Δ PI at the time of discharge from the PACU was 66.2%, and the 99% confidence interval was 12.2%~120.3%. The perfusion index was increased, and the VAS score was decreased significantly after analgesics were administered, but the correlation was weak in each subgroup. The VAS score is a subjective and psychometric parameter. The PI increased when partial pain relief was achieved after morphine was administered but did not reflect pain intensity or changes in the VAS score regardless of age or BMI. A percentage change in ΔPI at the time of discharge from the PACU relative to baseline PI measurements of greater than 12% can be used as a supplemental objective discharge criterion for pain assessment in the postanesthesia care unit.

Citation: Chu C-L, Huang Y-Y, Chen Y-H, Lai L-P, Yeh H-M (2018) An observational study: The utility of perfusion index as a discharge criterion for pain assessment in the postanesthesia care unit. PLoS ONE 13(5): e0197630. https://doi.org/10.1371/journal.pone.0197630

Editor: Chun-Pin Lin, National Taiwan University, School of Dentistry, TAIWAN

Received: February 26, 2018; Accepted: May 5, 2018; Published: May 16, 2018

Copyright: © 2018 Chu et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the paper and its Supporting Information files.

Funding: The authors received no specific funding for this work.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Pain is a subjective sensation that can negatively impact psychological and physiological wellbeing. It can stimulate the sympathetic nerve system and release stress hormones leading to increased oxygen consumption and even resulting in myocardial ischemia in serious cases [ 1 ]. Reducing pain during surgery and preventing and managing pain post-operatively is of crucial importance in the perioperative period [ 2 ], and patients care greatly about this issue.

Caregivers prescribe analgesics based on the extent of surgery and their experiences in the postanesthesia care unit (PACU). They also use the visual analogue scale (VAS) score or numeric rating scale (NRS) to subjectively estimate pain severity according to patients’ facial expressions and self-reported pain scores. Then, they select the appropriate analgesic and evaluate the response to treatment. However, there are still cases of pain that remain unresolved or undertreated because the patients were unable to express themselves adequately, such as in patients with mental retardation or dementia. Several studies regarding objective pain assessment tools, such as the surgical stress index during anesthesia [ 3 ] and the analgesic nociception index in the postanesthesia care unit [ 4 ], to supplement subjective feedback have been reported.

The perfusion index (PI), which is the ratio between the variable pulsatile (DC) and nonpulsatile (AC) signals, is an indirect and noninvasive measurement of peripheral perfusion [ 5 ]. It is calculated by means of pulse oximetry by expressing the pulsatile signal (during arterial flow) as a percentage of the nonpulsatile signal (AC/DC X 100), both of which are derived from the amount of infrared (940 nm) light absorbed. The PI may decrease due to increased vasomotor tone and the contraction of peripheral blood vessels when the sympathetic nervous system is activated by pain [ 6 ]. The PI may also increase when pain is relieved by the use of adequate analgesics [ 7 ]. In this study, we correlated the perfusion indices and visual analogue scale scores of patients to test if the perfusion index is a useful marker for objectively assessing pain relief in the PACU. We also compared the change in PI (ΔPI) at the time of discharge from the postanesthesia care unit with baseline PI measurements to evaluate if the PI is a useful criterion for discharging patients from the postanesthesia care unit.

Materials and methods

Ethics declaration.

The protocol used in this study was approved by the Institutional Ethics Review Board of National Taiwan University Hospital (Registry Number: 201604074RINB), and informed consent was waived based on its retrospective design. This study was carried out according to the International Conference on Harmonisation (ICH)/WHO Good Clinical Practice (GCP) guidelines and conformed to the principles outlined in the Declaration of Helsinki.

Study design and subjects.

This was an observational, retrospective, and single-center study. We reviewed medical records and enrolled female patients aged from 20 to 80 years old with an ASA class of I~III who were scheduled for gynecologic or general surgery and were admitted to the postanesthesia unit at National Taiwan University Hospital between November 2015 and May 2016. The exclusion criteria included patients who had unstable vital signs, those who were admitted as emergency cases, those who were intubated, those who were medicated with sedative or vasoactive agents, those who had been diagnosed with peripheral occlusive artery disease, and those who were admitted to the intensive care unit. The patients were monitored with automated noninvasive blood pressure on one arm, a 3-lead electrocardiogram, and a Masimo Radical 7 pulse oximeter probe (Masimo Crop, Irvine, California) on the contralateral index finger for continuous monitoring until discharge from the postanesthesia care unit. The room temperature was maintained at 22°C, and general anesthesia was induced with fentanyl at 1~2 μg/kg, propofol at 1.5~2 mg/kg, and cisatracurium at 0.2 mg/kg. After tracheal intubation, inhalational sevoflurane or desflurane was maintained at a concentration of 1 to 1.3 MAC and adjusted according to the patient’s vital signs. After surgery was finished, patients were administered reversal agents (2.5 mg of neostigmine and 0.4 mg of glycopyrrolate 0.4 mg) when spontaneously breathing was regained, and then the patients were sent to the postanesthesia care unit for observation. According to chart record, baseline data (T0) including perfusion index, temperature, heart rate, mean blood pressure, and SpO2 were recorded 5 minutes after entering the operating room. Postanesthetic data (P0) were recorded when the patients were admitted to the PACU after surgery. The perfusion index and visual analogue scale (VAS) score were recorded when the patients regained consciousness and asked for analgesics for the first time (P1), the second time (P2), and the third time (P3). The PI and VAS were recorded as P10, P20, and P30, 5 minutes after 3 mg of morphine was administered intravenously. Before discharge from the postanesthesia care unit, the PI and VAS were recorded at time point P9. The primary hypothesis of our study was that perfusion index is correlated with VAS, and the secondary hypothesis was that the percentage change of the perfusion index would be useful as a discharge criterion for assessing the wellbeing of the patients.

Statistical analysis

We used GraphPad Prism 6 to perform the statistical analysis. Continuous data are shown as the mean ± SD, and categorical data are shown as percentages. The Shapiro-Wilk test was used to test the normality of the distribution. We used the Wilcoxon signed-rank test or the paired t -test to separately compare the differences between repeated measurements of non-parametric and normally distributed data. The Friedman test was also used to compare the PI measured at different time points. Patients were divided into age subgroups and BMI subgroups and the difference of parameters before and after analgesic administration between these subgroups were compared by Kruskal–Wallis test. Correlation between the PI and the VAS was tested by Persons’ correlation coefficient in age, BMI subgroups, and all measurements. To reduce the bias of individual variation in perfusion index, we also evaluate the correlation between the ΔPI (PI after analgesic administration—PI before analgesic administration) and ΔVAS (VAS after analgesic administration—VAS before analgesic administration), and the percentage change in ΔPI (ΔPI/PI before analgesic administration) and the percentage change in ΔVAS (ΔVAS/VAS before analgesic administration). The PI measurements at the time when the patients met the discharge criteria were compared with the baseline PI measurements. The percentage change in Δ PI (P9-P0/P0) at the time of discharge from the postanesthesia care unit was calculated, and 99% confidence intervals were constructed to evaluate the use of this measure as a discharge criterion, along with VAS scores < 3. All the tests were 2-tailed, and p < 0.01 was considered statistically significant.

One hundred three patients were screened, and 80 patients met the inclusion criteria. The demographic data are shown in Table 1 . There were 64 and 16 female patients receiving gynecologic and general surgery, respectively. The average morphine consumption in the postanesthesia care unit was 4.5 mg, with an average number of analgesic requests of 1.5. The perfusion index was measured at different time point and is expressed as the mean ± standard deviation in Fig 1 . There was significant difference between the baseline PI (T0) and the PI at the time of arrival to postanesthesia care unit (P0) (p<0.001). The PI at the time of discharge from the postanesthesia care unit (P9) was not significantly different from the baseline PI (T0) (p = 0.1362).

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The perfusion index at the time of arrival to the postanesthesia care unit (PACU) was significantly different from the baseline PI. Differences in the PI between before and after the administration of analgesics also existed. There was no difference between the baseline PI and the PI at the time of discharge from the PACU.

https://doi.org/10.1371/journal.pone.0197630.g001

https://doi.org/10.1371/journal.pone.0197630.t001

In total, there were 123 requests for analgesic medication. The PI before analgesic administration (P1, P2, and P3) and the PI after analgesic administration (P10, P20, and P30) were significantly different (p < 0.0001). The VAS score and heart rate before and after analgesic administration also significantly changed (p < 0.0001) ( Table 2 ). The PI and the VAS score before and after analgesic administration, the ΔPI (PI after analgesic administration—PI before analgesic administration) and the ΔVAS (VAS after analgesic administration—VAS before analgesic administration), and the percentage change in ΔPI (ΔPI/PI before analgesic administration) and the percentage change in ΔVAS (ΔVAS/VAS before analgesic administration) were no significant difference between age and BMI subgroups as showed in S1 Table and were all weakly correlated ( Table 3 ). There was significant correlation between PI and VAS before and after analgesic administration (r = 0.742, 0.778 separately) in obesity group (BMI > 30 kg/m 2 ). All the patients had a VAS score < 3 with regard to their wellbeing when they were discharged from the postanesthesia care unit. The mean percentage change in ΔPI (P9-P0/P0) at the time of discharge from the postanesthesia care unit was 66.2%, and the 99% confidence interval was 12.2% ~ 120.3%.

https://doi.org/10.1371/journal.pone.0197630.t002

https://doi.org/10.1371/journal.pone.0197630.t003

The perfusion index (PI) is derived from plethysmography and is a non-invasive and convenient tool for evaluating peripheral perfusion. It can be used in routine anesthetic practice and can help anesthetists to make decisions based on its characteristics. Several studies were carried out in recent years because the perfusion index was thought to have become more stable and reliable [ 8 ]. It has been used to predict hypotension after spinal anesthesia during caesarean delivery [ 9 , 10 ] and as an early indicator of successful nerve block or sympathectomy [ 11 , 12 ]. It is also correlated with anesthetic depth [ 13 ] and can detect stress responses during anesthesia [ 7 ]. A decreased PI was associated with changes in position in critically ill non-intubated patients, and the correlation between changes in the PI and changes in BPS-NI values was positive [ 6 ]. Perfusion index as a tool for monitoring acute post-operative pain has been surveyed, but its correlation with visual analogue scale scores was not statistically significant [ 14 ].

In our study, the PI at the time of arrival to the postanesthesia care unit was lower than the baseline PI as a result of acute post-operative pain. There was a significant change in heart rate, PI, and VAS before and after the administration of intravenous morphine. Pain can stimulate a sympathetic reaction that increases heart rate and results in peripheral vasoconstriction, leading to a decreased PI. Morphine is an effective and safe analgesic medication for managing acute post-operative pain that can be given incrementally [ 15 ]. When acute post-operative pain was well managed, the PI increased, and the VAS score decreased significantly. When patients requested more analgesia and reported a VAS score of more than 5, the PI increased further after the second administration of intravenous morphine.

Like in a previous study, the correlation between the perfusion index and the VAS score was not established in our study. The ΔPI and ΔVAS were not significantly correlated, and the percentage changes in ΔPI and ΔVAS were also not significantly different. There was still no significant correlation in age and BMI subgroups with exception of PI and VAS before and after analgesic administration in obesity group (BMI > 30 kg/m 2 ) This can be explained because the VAS score is subjective and is based on psychometric properties. Patients may still report higher VAS scores when they suffer from poor emotional and psychological wellbeing even if analgesics are administered. The PI increased due to partial pain relief when analgesics were administered but did not reflect the VAS scores that the patients subjectively reported. This irrelevant phenomenon existed regardless of age and BMI. The only significant correlation between PI and VAS before and after analgesic was due to rather few measurements in morbid obesity group.

The criteria for discharge from the postanesthesia care unit included full recovery of consciousness, adequate respiration, and stable blood pressure and heart rate. Adequate pain control with a VAS score < 3 was also one of the criteria. All the patients who were discharged from the postanesthesia care unit were treated and had VAS scores < 3 in this study. We compared the patients’ baseline PI measurements with the PI at the time of discharge from the PACU and found that there was no significant difference. The mean of the percentage change in ΔPI was 66.2% with a 99% confidence interval of 12.2% ~ 120.3%. Individual baseline variation in PI measurements has been lessened by using this parameter, but there is still wide range of data distribution. Most patients discharged from the PACU were in good condition and reported VAS scores < 3 with the percentage change in ΔPI at the time of discharge from the postanesthesia care unit greater than 12%. As the above result shows, the percentage change in ΔPI can be used as a supplemental objective pain evaluation tool in the postanesthesia care unit if the patient is unconscious and cannot properly report a VAS score.

The major limitation of our study is that we included only female patients who underwent gynecological or general surgery in order to achieve homogeneity. However, older women showed less significant changes in PI as measured by electrical stimulation [ 16 ]. This may have lessened the significance of the changes in perfusion index and VAS and have led to negative results. Patients who were using patient-controlled analgesia were not included in our study and who failed to meet PACU discharge criterion were not included as contrast group. A large-scale study including a larger range of surgeries and patient groups is needed to explore the utility of perfusion index measurements in anesthetic management.

We used perfusion index as a supplemental tool for pain assessment in the postanesthesia care unit. PI values increased when intravenous analgesics were administered, but the correlation of the PI with VAS was poor due to the subjectivity of VAS. We also used the percentage change in ΔPI at the time of discharge from the PACU as a discharge criterion to lessen inter-individual variation. We came to the conclusion that a percentage change in the perfusion index at the time of discharge from the postanesthesia care unit relative to baseline PI measurements of more than 12% can be used as a supplemental objective discharge criterion for pain assessment in the postanesthesia care unit.

Supporting information

S1 table. difference of parameters between age and bmi groups..

https://doi.org/10.1371/journal.pone.0197630.s001

S2 Table. STROBE statement checklist.

https://doi.org/10.1371/journal.pone.0197630.s002

S3 Table. Protocol of study.

https://doi.org/10.1371/journal.pone.0197630.s003

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The perfusion index is a useful screening tool for peripheral artery disease

• Original Article
• Published: 03 October 2018
• Volume 34 , pages 583–589, ( 2019 )

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• Hiroshi Okada 1 ,
• Muhei Tanaka 2 ,
• Takashi Yasuda 3 ,
• Tadaaki Kamitani 4 ,
• Hisahiro Norikae 5 ,
• Tetsuya Fujita 5 ,
• Takashi Nishi 5 ,
• Hirokazu Oyamada 6 ,
• Tetsuro Yamane 7 &
• Michiaki Fukui 8  

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The number of people with peripheral artery disease (PAD) has been increasing globally; therefore, it is important to explore more options to screen patients who are at a risk of developing PAD. The perfusion index (PI) represents the degree of circulation through the peripheral tissues and is measured noninvasively. We investigated the correlation between the PI and ankle-brachial index (ABI) to explore whether the PI could be used a screening tool for PAD. This cross-sectional study included 390 patients. We measured the ABI and PI for all patients. The median ABI value was 1.06 (0.92–1.13); the PI was 1.7% (0.9–3.5). The PI was higher in men than in women ( P  < 0.0001). The PI was positively correlated with the estimated glomerular filtration rate and ABI in both men and women. The sensitivity and specificity of the PI to predict PAD (ABI ≤0.9) were 90.0% and 80.3%, respectively, and the cutoff PI value was 1.5% in men. The sensitivity and specificity of the PI to predict PAD were 82.1% and 79.2%, respectively, and the cutoff PI value was 1.1% in women. PI could be a reliable screening tool for diagnosing PAD because it does not restrict the patient’s mobility, can be completed in a short time period, and is associated with reduced costs.

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Use of the ankle-brachial index combined with the percentage of mean arterial pressure at the ankle to improve prediction of all-cause mortality in type 2 diabetes mellitus: an observational study

Fowkes FG, Rudan D, Rudan I, Aboyans V, Denenberg JO, McDermott MM, Norman PE, Sampson UK, Williams LJ, Mensah GA, Criqui MH (2013) Comparison of global estimates of prevalence and risk factors for peripheral artery disease in 2000 and 2010: a systematic review and analysis. Lancet 382:1329–1340

Article   PubMed   Google Scholar  

Norgren L, Hiatt WR, Dormandy JA, Nehler MR, Harris KA, Fowkes FG, TASC II Working Group (2007) Inter-society consensus for the management of peripheral arterial disease (TASC II). J Vasc Surg 45:S5–S67

Diehm C, Allenberg JR, Pittrow D, Mahn M, Tepohl G, Haberl RL, Darius H, Burghaus I, Trampisch HJ, German Epidemiological Trial on Ankle Brachial Index Study Group (2009) Mortality and vascular morbidity in older adults with asymptomatic versus symptomatic peripheral artery disease. Circulation 120:2053–2061

Yamazaki T, Goto S, Shigematsu H, Shimada K, Uchiyama S, Nagai R, Yamada N, Matsumoto M, Origasa H, Bhatt DL, Steg PG, Ikeda Y, REACH Registry Investigators (2007) Prevalence, awareness and treatment of cardiovascular risk factors in patients at high risk of atherothrombosis in Japan. Circ J 71:995–1003

Gerhard-Herman MD, Gornik HL, Barrett C, Barshes NR, Corriere MA, Drachman DE, Fleisher LA, Fowkes FG, Hamburg NM, Kinlay S, Lookstein R, Misra S, Mureebe L, Olin JW, Patel RA, Regensteiner JG, Schanzer A, Shishehbor MH, Stewart KJ, Treat-Jacobson D, Walsh ME (2017) 2016 AHA/ACC guideline on the management of patients with lower extremity peripheral artery disease: executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. Circulation 135:e686–e725

PubMed   Google Scholar  

Lima AP, Beelen P, Bakker J (2002) Use of a peripheral perfusion index derived from the pulse oximetry signal as a noninvasive indicator of perfusion. Crit Care Med 30:1210–1213

Expert Committee on the Diagnosis and Classification of Diabetes Mellitus (2003) Report of the expert committee on the diagnosis and classification of diabetes mellitus. Diabetes Care 26:S5–S20

Article   Google Scholar  

Matsuo S, Imai E, Horio M, Yasuda Y, Tomita K, Nitta K, Yamagata K, Tomino Y, Yokoyama H, Hishida A (2009) Collaborators developing the Japanese equation for estimated GFR. Revised equations for estimated GFR from serum creatinine in Japan. Am J Kidney Dis 53:982–992

Article   CAS   PubMed   Google Scholar  

Quinn CT, Raisis AL, Musk GC (2013) Evaluation of Masimo signal extraction technology pulse oximetry in anaesthetized pregnant sheep. Vet Anaesth Analg 40:149–156

Yamashina A, Tomiyama H, Takeda K, Tsuda H, Arai T, Hirose K, Koji Y, Hori S, Yamamoto Y (2002) Validity, reproducibility, and clinical significance of noninvasive brachial-ankle pulse wave velocity measurement. Hypertens Res 25:359–364

Criqui MH, Fronek A, Barrett-Connor E, Klauber MR, Gabriel S, Goodman D (1985) The prevalence of peripheral arterial disease in a defined population. Circulation 71:510–515

Hiatt WR, Hoag S, Hamman RF (1995) Effect of diagnostic criteria on the prevalence of peripheral arterial disease. The San Luis Valley Diabetes Study. Circulation 91:1472–1479

Criqui MH, Langer RD, Fronek A, Feigelson HS, Klauber MR, McCann TJ, Browner D (1992) Mortality over a period of 10 years in patients with peripheral arterial disease. N Engl J Med 326:381–386

Kobayashi M, Shindo S, Kubota K, Kojima A, Ishimoto T, Iyori K, Tada Y (2000) Causes of late mortality in patients with disabling intermittent claudication. Jpn Circ J 64:925–927

Imparato AM, Kim GE, Davidson T, Crowley JG (1975) Intermittent claudication: its natural course. Surgery 78:795–799

CAS   PubMed   Google Scholar  

Dormandy J, Heeck L, Vig S (1999) The fate of patients with critical leg ischemia. Semin Vasc Surg 12:142–147

Hirsch AT, Criqui MH, Treat-Jacobson D, Regensteiner JG, Creager MA, Olin JW, Krook SH, Hunninghake DB, Comerota AJ, Walsh ME, McDermott MM, Hiatt WR (2001) Peripheral arterial disease detection, awareness, and treatment in primary care. JAMA 286:1317–1324

Davies JH, Kenkre J, Williams EM (2014) Current utility of the ankle-brachial index (ABI) in general practice: implications for its use in cardiovascular disease screening. BMC Fam Pract 15:69

Article   PubMed   PubMed Central   Google Scholar  

Potier L, Halbron M, Bouilloud F, Dadon M, Le Doeuff J, Van Ha G, Grimaldi A, Hartemann-Heurtier A (2009) Ankle-to-brachial ratio index underestimates the prevalence of peripheral occlusive disease in diabetic patients at high risk for arterial disease. Diabetes Care 32:e44

Santoro L, Flex A, Nesci A, Ferraro PM, De Matteis G, Di Giorgio A, Giupponi B, Saviano L, Gambaro G, Franceschi F, Gasbarrini A, Landolfi R, Santoliquido A (2018) Association between peripheral arterial disease and cardiovascular risk factors: role of ultrasonography versus ankle-brachial index. Eur Rev Med Pharmacol Sci 22:3160–3165

Santoro L, Ferraro PM, Flex A, Nesci A, De Matteis G, Di Giorgio A, Zaccone V, Gambaro G, Gasbarrini A, Santoliquido A (2016) New semiquantitative ultrasonographic score for peripheral arterial disease assessment and its association with cardiovascular risk factors. Hypertens Res 39:868–873

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Department of Diabetes and Endocrinology, Matsushita Memorial Hospital, 5-55 Sotojima-cho, Moriguchi, 570-8540, Japan

Hiroshi Okada

Department of Internal Medicine, Kyotamba Hospital, Kyotamba, Japan

Muhei Tanaka

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Takashi Yasuda

Department of Cardiology, Matsushita Memorial Hospital, Moriguchi, Japan

Tadaaki Kamitani

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Hisahiro Norikae, Tetsuya Fujita & Takashi Nishi

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Hirokazu Oyamada

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Michiaki Fukui received grants from the Japan Society for the Promotion of Science, AstraZeneca Plc, Astellas Pharma Inc., Nippon Boehringer Ingelheim Co., Ltd., Daiichi Sankyo Co., Ltd., Eli Lilly Japan K.K., Kyowa Hakko Kirin Company Ltd., Kissei Pharmaceutical Co., Ltd., MSD K.K., Mitsubishi Tanabe Pharma Corporation, Novo Nordisk Pharma Ltd., Sanwa Kagaku Kenkyusho Co., Ltd., Sanofi K.K., Ono Pharmaceutical Co., Ltd., and Takeda Pharmaceutical Co., Ltd., outside the submitted work. The sponsors were not involved in the study design; the collection, analysis, and interpretation of data; the writing of this manuscript; or the decision to submit the article for publication. The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article. The authors declare that although they are affiliated with a department that is supported financially by a pharmaceutical company, the authors received no current funding for this study, and this does not alter their adherence to all the journal policies on sharing data and materials. The other authors have no conflict of interest to disclose.

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Okada, H., Tanaka, M., Yasuda, T. et al. The perfusion index is a useful screening tool for peripheral artery disease. Heart Vessels 34 , 583–589 (2019). https://doi.org/10.1007/s00380-018-1276-4

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Received : 28 May 2018

Accepted : 28 September 2018

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DOI : https://doi.org/10.1007/s00380-018-1276-4

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Perfusion Index: Physical Principles, Physiological Meanings and Clinical Implications in Anaesthesia and Critical Care.

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• Volume 07 Issue 03 March 2019
• Role of Perfusion Index as a Predictor of Hypotension during Spinal Anaesthesia for Caesarean Section-A Prospective Study
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Title:  Role of Perfusion Index as a Predictor of Hypotension during Spinal Anaesthesia for Caesarean Section-A Prospective Study

Authors: Dr Joseph George, Dr Sebastian S Valiaveedan, Dr Mariam Koshi Thomas

Corresponding Author

Background: Many attempts have been made to look for predictors of hypotension during spinal anaesthesia. Perfusion index (PI) obtained from pulse oximeter has been recently come into focus as predictor of hypotension during spinal anaesthesia for lower segment caesarean section (LSCS).

Aims and Objectives : To estimate the correlation between baseline perfusion index and incidence of hypotension following sub arachnoid block in LSCS.

Materials and Methods: In this prospective observational study, thirty parturients belonging to American society of Anesthesiologists (ASA) physical status 1 or 2 with uncomplicated pregnancies scheduled for elective caesarean section under spinal anaesthesia were included in the study. Spinal anaesthesia was performed with 2ml of 0.5% bupivacaine (hyperbaric) at L3-L4 or L2-L3 interspinous space using a 25G Quincke needle. Hypotension is defined as a decrease in systolic blood pressure (SBP) > 25% from baseline.

Results: The incidence of hypotension among study subjects was 66.7% There was significant correlation between baseline PI and fall in SAP from baseline (r= 0.368, P < 0.05).The optimal cutoff point across a range of cutoff points for PI was found to be 3.6 with a sensitivity of 80% and specificity of 60%,

Conclusion: Baseline perfusion index >3.6 is associated with a higher incidence of hypotension following spinal anaesthesia in elective LSCS.

• Reynolds F, Seed PT. Anaesthesia for Caesarean section and neonatal acid‐ base status: a meta‐ Anaesthesia. 2005 Jul 1;60(7):636-53.
• Shnider SM, Asling JH, Morishima HO. Vasopressors in obstetrics: II. Fetal hazards of methoxamine administration during obstetric spinal anesthesia. American journal of obstetrics and gynecology. 1970 Mar 1;106(5):680-6
• Chumpathong S, Chinachoti T, Visalyaputra S, Himmunngan T .Incidence and risk factors of Hypotension during spinal anesthesia for caesarean section at Siriraj Hospital J.MedAssoc Thai 2006; 89(8):1127-32
• Gaiser R. Physiological changes of pregnancy. In: Chestnut DH, editor. Chestnut’s Obstetric Anaesthesia: Principles and Practice. 5th ed. Philadelphia: Mosby Elsevier Publishing; 2014. p. 15‑
• Frolich MA, Caton D. Baseline heart rate may predict hypotension after spinal anesthesia in prehydrated obstetrical patients. Can J Anaesth. 2002;49:185–189
• Hanss R, Bein B, Francksen H, Scherkl W, Bauer M, Doerges V, et al. Heart rate variability-guided prophylactic treatment of severe hypotension after subarachnoid block for elective cesarean delivery. Anesthesiology.2006;104 :635–643.
• Orbach-Zinger S, Ginosar Y, Sverdlik J, Treitel C, MacKersey K, Bardin R et al. Partnerʼs Presence During Initiation of Epidural Labor Analgesia Does Not Decrease Maternal Stress. Anesthesia & Analgesia. 2012;114(3):654-660.
• Nani FS, Torres MLA. Correlation between the body mass index (BMI) of pregnant women and the development of hypotension after spinalanesthesia for cesarean section. Rev Bras Anestesiol. 2011;61:21–30
• Huang B, Sun K, Zhu Z, Zhou C, Wu Y, Zhang F et al. Oximetry-derived perfusion index as an early indicator of CT-guided thoracic sympathetic blockade in palmar hyperhidrosis. Clinical Radiology. 2013;68(12):1227-1232
• Ginosar Y, Weiniger CF, Meroz Y, Kurz V, Bdolah‑Abram T, Babchenko A, et al. Pulse oximeter perfusion index as an early indicator of sympathectomy after epidural anesthesia. Acta Anaesthesiol Scand 2009;53:1018‑
• Mowafi HA, Ismail SA, Shafi MA, Al‑Ghamdi AA. The efficacy of perfusion index as an indicator for intravascular injection of epinephrine‑ containing epidural test dose in propofol‑ anesthetized adults. Anesth Analg 2009;108:549‑
• Lima AP, Beelen P, Bakker J. Use of a peripheral perfusion index derived from the pulse oximetry signal as a noninvasive indicator of perfusion. Crit Care Med 2002;30:1210‑
• Park GE, Hauch MA, Curlin F, Datta S, Bader AM. The effects of varying volumes of crystalloid administration before cesarean delivery on maternal hemodynamics and colloid osmotic pressure. Anesth Analg 1996;83:299‑303
• Toyama S, Kakumoto M, Morioka M, Matsuoka K, Omatsu H, Tagaito Y, et al. Perfusion index derived from a pulse oximeter can predict the incidence of hypotension during spinal anaesthesia for caesarean delivery. Br J Anaesth 2013;111:235‑
• Cannesson, M., Delannoy, B., Morand, A., Rosamel, P., Attof, Y., Bastien, O. and Lehot, J. (2008). Does the Pleth Variability Index Indicate the Respiratory-Induced Variation in the Plethysmogram and Arterial Pressure Waveforms? Anesthesia & Analgesia, 106(4), pp.1189-1194
• Ajne G, Ahlborg G, Wolff K, Nisell H. Contribution of endogenous endothelin‑1 to basal vascular tone during normal pregnancy and preeclampsia. Am J Obstet Gynecol 005;193:234‑40
• Yokose M, Mihara T, Sugawara Y, Goto T. The predictive ability of non‑invasive haemodynamic parameters for hypotension during caesarean section: A prospective observational study. Anaesthesia 2015;70:555‑

Dr Sebastian S Valiaveedan

Department of Anaesthesiology and critical care, Jubilee Mission Medical College and Research Institute Thrissur, Kerala, India

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Perfusion index in newborn infants: a noninvasive tool for neonatal monitoring

Affiliation.

• 1 Research Intern at the Orthopaedic Department, Children's Hospital Los Angeles, Los Angeles, California, USA.
• PMID: 24471645
• DOI: 10.1111/apa.12574

Aim: To review the utility of perfusion index (PI) in the evaluation of neonatal clinical conditions. Twenty-five manuscripts were reviewed. PI provides information about haemodynamic stability, illness severity, early neonatal respiratory outcome, low superior vena cava flow and subclinical chorioamnionitis.

Conclusion: PI is a valuable tool to assess the newborn's health condition and could become a standardised measure in clinical evaluation. Different study designs are necessary to provide further validation to this method.

Keywords: Cardiovascular function; Haemodynamics; Illness severity; Newborns; Perfusion index.

©2014 Foundation Acta Paediatrica. Published by John Wiley & Sons Ltd.

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