Surgical Pleth Index and Analgesia Nociception Index for intraoperative analgesia in patients undergoing neurosurgical spinal procedures: a comparative randomized study

BACKGROUND: The Surgical Plethysmographic Index (SPI) and the Analgesia Nociception Index (ANI) have been suggested for the non-invasive intraoperative monitoring of nociceptionianti-nociception balance. We aimed to compare patterns of intraoperative use of opioids, postoperative cortisol levels and postoperative pain scores after intraoperative analgesia guided either by ANI, SPI or anesthesiologist's judgment. METHODS: Seventy-two adult ASA I-III patients scheduled for elective neurosurgical spinal procedures were randomized into the ANI group, SPI group and control group. Anesthesia and intraoperative use of opioids (sufentanil boluses based on body weight) were managed according to a strict protocol. The use of sufentanil was targeted to keep ANI value 50-70 in the ANI group, SPI value below individual postinduction baseline value plus 10 points in the SPI group. In the control group, the use of opioids was left at anesthesiologist's discretion. RESULTS: Additional sufentanil boluses were administered earlier in the ANI and SPI groups in comparison to the control group (third dose after 51.8 +/- 22.1 vs 52.7 +/- 14.8 vs. 84.5 +/- 24.8 min respectively, P=0.001; fourth dose after 61.3 +/- 30.1 vs. 57.2 +/- 14.1 vs. 120.0 +/- 26.2 min, P=0.003, and fifth dose after 78.8 +/- 33.7 vs. 74.0 +/- 11.6 vs. 146.7 +/- 23.2 min respectively, P=0.009). There were no differences in postoperative cortisol levels, time to spontaneous breathing at the end of anesthesia and postoperative pain scores. CONCLUSIONS: Both ANI and SPI guidance significantly modified intraoperative opioid use, but no modification of postoperative cortisol levels and postoperative pain was observed.