Comparison of End-tidal Sevoflurane Concentration Required for Optimal Depth of Anesthesia during Opioid-free General Anesthesia Using Intravenous Lignocaine versus Morphine.

Background and aims: In opioid-free anesthesia (OFA) protocol, intravenous lignocaine can offer perioperative analgesic benefits. However, maintaining adequate anesthetic depth during OFA, particularly with neuromuscular blockade, poses a challenge due to the unreliable nature of hemodynamic parameters as indicators of anesthetic depth. We aimed to compare the end-tidal sevoflurane concentration needed to maintain bispectral index (BIS) values of 40-60 in patients undergoing major head-and-neck cancer surgery using lignocaine-based OFA versus a morphine-based regimen.

Methods: This prospective, randomized, double-blind study enrolled 30 patients undergoing wide excision and reconstruction for head-and-neck cancer. Group L received a lignocaine bolus (1.5 mg/kg) and infusion (1 mg/kg/h), while Group B received a morphine bolus (0.2 mg/kg) and 2 mg/h infusion. Propofol was used to induce anesthesia, and nasal intubation was carried out. Sevoflurane in a 1:1 air-oxygen mixture was used for maintenance, titrated to maintain BIS values between 40 and 60. Additional analgesics were added if indicated.

Results: End-tidal sevoflurane concentration and sevoflurane consumption were significantly higher in Group L. Hypertension was significantly more frequent in Group L and required significantly more additional analgesics (P < 0.001). Mean heart rate was higher in Group L immediately after induction and at 1 min postintubation, while it was lower at 60 min postintubation. Neither group reported any incidence of intraoperative awareness.

Conclusion: Lignocaine-based OFA required a significantly higher end-tidal sevoflurane to maintain sufficient anesthetic depth compared to morphine-based anesthesia. In addition, sevoflurane use, intraoperative hypertension, and the need for supplemental analgesics were notably greater in the OFA group.