Comparison of analgesia nociception index, surgical pleth index and hemodynamic parameters between patients receiving fentanyl versus dexmedetomidine analgesia for supratentorial craniotomy - an open label active-controlled randomized trial

Dexmedetomidine decreases heart rate (HR) and increases high frequency (HF) component of HR variability (HRV). Analgesia Nociception Index (ANI) measures nociception by analyzing the influence of respiration on HF component of HRV while surgical pleth index (SPI) derives this information from photoplethymographic signals of finger arterioles. Therefore, during administration of dexmedetomidine, reliability of ANI may vary. This study compared the changes in ANI, SPI and hemodynamics (HR and mean arterial pressure [MAP]) during various noxious stimuli with fentanyl and dexmedetomidine intraoperative analgesia. In this trial, patients undergoing elective supratentorial surgery under general anesthesia were randomized to receive either fentanyl or dexmedetomidine infusion for intraoperative analgesia. ANI (instantaneous and mean), SPI, HR and MAP were compared before and after noxious stimuli (intubation, skull pin insertion, skin incision and craniotomy) with respect to magnitude of maximum change in the variable and the time taken for the maximal change (defined as response time) between the groups. A total of 58 patients, 29 in each group were recruited into the study. At intubation, SPI changed significantly more in the fentanyl group compared to dexmedetomidine group (37 versus 20 units, p = 0.007). At skull pinning, ANI values (both instantaneous and mean) changed more in dexmedetomidine group (p = 0.024 and 0.009) with significantly longer response time (p = 0.039). There was no difference between the groups with respect to any of the variables at skin incision and craniotomy. ANI during use of dexmedetomidine and SPI while using fentanyl, might be the better choices as intraoperative nociception monitors.