Entropy as an Indicator to Measure Depth of Anaesthesia for Laryngeal Mask Airway (LMA) Insertion during Sevoflurane and Propofol Anaesthesia.

Abstract

Assessment of the depth of anaesthesia is fundamental to the anaesthetic practice. Entropy measurement is an objective monitoring and is of two types- Response Entropy (RE) and State Entropy (SE) indicating analgesic and hypnotic levels during general anaesthesia. The aim of our study was to assess the depth of anaesthesia for LMA placement using entropy as a tool. The assessment of entropy as an indicator of depth of anaesthesia in the form of haemodynamic variations and success rate of LMA placement. A prospective study was carried out after ethical committee approval in 100 patients, aged 20-50 years, with ASA grade I and II of either gender undergoing elective surgery lasting less than two hours under general anaesthesia. Anaesthesia was induced with sevoflurane 2.5% and IV propofol at 6 ml/min until entropy value fell from baseline values to 30-40 and then LMA insertion was performed. SE and RE values were noted every 30 seconds for five minutes. Mean blood pressure and heart rate were recorded every minute after induction for 5 minutes. There was a significant change in RE and SE values within 30 seconds from start of induction. Desired values of RE (40.10±2.52) and SE (39.2±2.47) were achieved at 120 seconds to 150 seconds. Mean dose of propofol used during surgery was 86.5±3.5 mg and mean insertion time was 110±12 seconds Patients in study group had a stable haemodynamics throughout the procedure, (p-value -0.8). Entropy is a reliable indicator to assess depth of anaesthesia for LMA placement during sevoflurane and propofol anaesthesia.