Quantifying influence of epidural analgesia on entropy guided general anaesthesia using sevoflurane - A randomised controlled trial

Background and Aims: Minimum alveolar concentration (MAC) of inhalational agent denotes the requirement of it to maintain adequate plane of general anaesthesia. The precision to the maintenance of anaesthesia can be further guided by use of entropy to titrate the depth of anaesthesia. Regional anaesthesia and the concomitant deafferentation will decrease the need of general anaesthetics. We conducted a randomised double-blind trial to quantify the effect of addition of regional anaesthesia to sevoflurane based general anaesthesia technique guided by entropy to achieve satisfactory depth of anaesthesia. Methods: Forty patients posted for elective laparotomies were randomised to two groups. All patients received a bolus followed by an epidural infusion. Group GE (general anaesthesia + epidural bupivacaine) received 0.25% epidural bupivacaine and Group GS received epidural saline. Both groups received narcotic, relaxant and sevoflurane anaesthesia guided by entropy monitoring. The state entropy (SE) was maintained at 40-60 by titrating end tidal sevoflurane concentration (ETsevo). Heart rate, blood pressure, SpO2, end tidal carbon dioxide (ETCO2) and sevoflurane were recorded. Results: Both groups were similar in heart rate and mean blood pressure during anaesthesia maintenance. The minimum ETSevorequired to maintain entropy between 40 and 60 in group GE was 0.53% compared to 0.95% in group GS the epidural saline group (P < 0.001). The end-tidal sevoflurane requirement to maintain adequate depth of anaesthesia dropped by 44.2% in group GE.Conclusion: Lower concentrations of volatile anaesthetic are required when entropy-guided general anaesthesia is combined with regional blockade.