Perfusion Index as a Predictor of Successful Spinal Anaesthesia: A Time-dependent ROC Curve Analysis

Abstract

The aim of this study was to evaluate the changes in perfusion index (PI), skin temperature, and mean arterial pressure (MAP) during spinal anesthesia and to determine the success of spinal anesthesia using the PI values.Methods: A total of 128 patients belonging to American Society of Anesthesiologists' physical status I-II undergoing elective surgery under spinal anesthesia at the T10 level were included in this study. MAP, heart rate, body temperature, PI, and spinal anesthesia level, determined with the pinprick test, were recorded from baseline to 30 min following anesthesia induction. Repeated measures ANOVA test was used to evaluate changes after spinal block and linear mixed models were created. Time-dependent receiver operating characteristics (ROC) curves, using post-anesthetic 2 nd min PI measurements and time to T10 spinal anesthesia level, were estimated to predict further successful spinal blockade. In addition, standard ROC curve analysis was performed for the PI ratios.Results: There was a significant linear increase in PI values (β=0.14, standard error = 0.01, p<0.001). Time-dependent ROC curves became significant for the post-anesthetic 6th min and after. Specificity was 100% after the 15 th min. The cutoff value of post-anesthetic 2nd min PI was 2.4 (Area under the ROC curve-AUC: 0.71, 95% confidence interval: 0.59-0.83, sensitivity: 47%, specificity: 100%) to predict successful spinal blockage for the 15 th min. In standard ROC curve analysis, only the 2 nd min ROC curve revealed a significant AUC. Conclusion:All of the patients whose PI measurement at the 2 nd min after the induction of anesthesia was above 2.4, reached the T10 spinal block level at the 15 th min after induction. This finding must be supported by the increasing trend in PI individually. Adaptation of the study findings to the operation room practice may be considered for the patients with limited compliance to the pinprick test.

Variability of perfusion index as a new parameter in different types of Anaesthesia techniques

“…Clinical studies in patients have demonstrated that an increase in perfusion index is an early indicator that anesthesia has initiated peripheral vasodilation that typically occurs with the onset of anesthetic effects. The present study hypothesizes that perfusion index will be a parameter to monitor hemodynamic changes in different techniques of anesthesia and correlates with onset of anesthesia 3 .…”

“…It helps in predicting hemodynamic responses to anesthetic techniques, drugs and intra-operative stimuli. A rise in PI from the baseline indicates the onset of successful anesthesia 3 .…”