Application of surgical pleth index in monitoring nociceptive stimulation in patients with total intravenous anesthesia

Objective To investigate the accuracy of surgical pleth index (SPI) in monitoring patients with nociceptive stimulation and its predictability for cardiovascular response to nociceptive stimulation in total intravenous anesthesia (TIVA). Methods A total of 102 patients (aged 18 to 65 years, ASAⅠtoⅡ, and BMI of 18.5 to 30 kg/㎡) who underwent elective thyroid surgery in our hospital from February to June 2022 were enrolled in this study. Each patient was induced by intravenous anesthesia, maintained by target-controlled infusion of propofol and remifentanil, and monitored by SPI for analgesia depth. The absolute values of SPI, heart rate (HR) and mean arterical pressure (MAP) of patients 2 min before and during nociceptive stimulation and the maximum values of SPI, HR and MAP within 2 min after nociceptive stimulation were recorded. Receiver operating characteristic (ROC) curve was used to analyze the accuracy of SPI, HR and MAP in monitoring nociceptive stimulation and the predictability of SPI in cardiovascular response to nociceptive stimulation. Results ROC curve analysis indicated that SPI (AUC=0.931, Cutoff value=30) was superior to HR (AUC=0.804, Cutoff value=68) and MAP (AUC=0.759, Cutoff value=80) in monitoring accuracy of tracheal intubation stimulation, ΔSPI (AUC=0.990, Cutoff value=4) was better than ΔHR (AUC=0.972, Cutoff value=3) and ΔMAP (AUC=0.854, Cutoff value=3), ΔSPI was better than SPI, ΔHR was better than HR, and ΔMAP was better than MAP, with their AUC values statistically different (P < 0.05). In terms of monitoring the accuracy of skin incisions, SPI (AUC=0.925, Cutoff value=43) was superior to HR (AUC=0.587, Cutoff value=65) and MAP (AUC=0.804, Cutoff value=76), ΔSPI (AUC=0.998, Cutoff value=7) was better than ΔHR (AUC=0.833, Cutoff value=1) and ΔMAP (AUC=0.943, Cutoff value=3), ΔSPI was better than SPI, ΔHR was better than HR, and ΔMAP was better than MAP, and the above AUC differences were statistically significant (P < 0.05); SPI had predictive value for the cardiovascular response stimulated by tracheal intubation (AUC=0.662, Cutoff value=17, P < 0.05), but had no predictive significance for the cardiovascular response stimulated by skin incisions (P>0.05). Conclusion The absolute value and change of SPI are better than the traditional hemodynamic indexes HR and MAP in monitoring the accuracy of nociceptive stimulation, which can accurately monitor nociceptive stimulation during operation. SPI has predictive value for the cardiovascular response stimulated by intubation stimulation, and has important clinical significance for judging the appropriate timing of intubation.