An observational study to evaluate the utility of surgical plethysmographic index as a tool to predict postoperative pain in patients receiving oral calcium channel blocker therapy.

Abstract

Background and aims: Surgical plethysmographic index (SPI) is a monitoring parameter used to predict postoperative pain. Our primary objective was to determine whether the value of SPI obtained 10 min before expected completion of surgery can be used as a reliable tool to predict postoperative pain in patients receiving oral calcium channel blocker (CCB) therapy for hypertension. Our secondary objective was to determine if SPI can be used as a tool to predict awakening of the patient from anesthesia.

Materials and methods: Seventy patients on CCB were enrolled. SPI values at 10 min before the anticipated end of the surgical procedure were recorded. The mean value of 10 readings was calculated and used as the SPI score for the patient. The time that anesthetic was cut off till the time of extubation was taken as the time of awakening. Numerical rating pain scale assessed the patient's level of postoperative pain 15 min after extubation. Thirty-five patients not on CCB were studied similarly to serve as controls. Data obtained were analyzed using Statistical Package for the Social Sciences version 28 for Windows through the Department of Medical Statistics. P value less than 0.05 was considered significant.

Results: In patients on CCB, based on the r value, a positive correlation was noted between the mean SPI and NRS values on scatterplot (P = 0.009). In patients not on CCB, a positive correlation was noted between mean SPI and NRS. In both groups, a negative correlation was noted between mean SPI and awakening time, which was not significant.

Conclusions: In patients receiving oral CCB, SPI values obtained 10 min before expected completion of surgery can be a reliable tool to predict postoperative pain, but not to predict awakening from anesthesia.