Analgesia Nociception Index-guided intraoperative fentanyl consumption and postoperative analgesia in patients receiving scalp block versus incision-site infiltration for craniotomy

BACKGROUND: Scalp block or local anesthetic infiltration for craniotomy blunts hemodynamic response to noxious stimuli, reduces opioid requirement and decreases postoperative pain. Analgesia Nociception Index (ANI) provides objective information about the magnitude of pain (rated from 0 to 100 with 0 indicating extreme nociception and 100 indicating absence of nociception) and adequacy of infra-operative analgesia. This study compared intra-operative fentanyl consumption guided by ANI and postoperative pain in patients who receive scalp block with those who receive incisionsite local anesthetic infiltration tier craniotomy. METHODS: Sixty adult patients undergoing elective supra-tentorial tumor surgery were randomly allocated to receive scalp block or incision-site infiltration after induction of anesthesia. Throughout the intra-operative period, patients received fentanyl 0.5 mu g/kg/h and ANI was continuously monitored. Fentanyl 1 mu g/kg bolus was administered when ANI decreased to <50. Intraoperative fentanyl consumption was compared using unpaired t-test. Correlation between ANI and postoperative numerical rating scale (NRS) pain score was done using Spearman's rho. RESULTS: The fentanyl consumption (mu g/kg/h) was less with scalp block when compared to incision-site infiltration (median [interquartile range]; 1.04 [0.92-1.34] vs. 1.34 [1.18-1.59], P=0.001). Postoperative pain scores were similar [median (interquartile range); 1.5 (0-4) vs. 3 (0-4), P=0.840]. No correlation was observed between postoperative NRS Score and ANI (correlation coefficient = 0.072; P=0.617). CONCLUSIONS: ANI-guided analgesic administration during craniotomy demonstrated lower intra-operative fentanyl consumption in patients receiving scalp block as compared to incision-site local anesthetic infiltration. No correlation was seen between postoperative NRS and ANI.