ABSTRACT
Introduction: Minimal alveolar concentration (MAC) ofvolatile anaesthetics is that which prevent movement in50% of subjects in response to a noxious stimulus. MACis influenced by several drugs like fentanyl, midazolam,propofol, clonidine. Various successful studies have been doneto demonstrate the effect of IV anaesthetics and opioids onMAC of various inhaled anaesthetics in balanced anaesthesiasettings. To assess the effect of a perioperative lidocaineinfusion on the MAC of isoflurane in a balanced anaesthesiatechnique by correlating it with the depth of anaesthesia asassessed by the Bispectral Index (BIS).Material and methods: It is a prospective randomized studyconsisting of 100 patients. The patients were categorized intogroup L and group S, Group L received a bolus of 1.5mg/kg of lidocaine five minutes before the induction of generalanaesthesia followed by 1.5mg/kg/hr of lidocaine infusiontill the end of the surgical procedure or upto a maximum ofthree hours (whichever was earlier). Group S received salinesimilarly. BIS was maintained between 40 to 60 and MAC ofisoflurane was measured in both group.Result: Significant difference with regard to MAC ofisoflurane used to maintain anaesthesia was noted betweenthe two groups. It was found overall average MAC ofisoflurane in Group L was (0.761±0.011) and control groupwas (0.885±0.020).Conclusion: Our study found that lidocaine loading dosefollowed by infusion significantly reduces volatile anaestheticrequirement as measured by MAC of isoflurane.