Predictive Accuracy of Gas Man® Simulation Model in Datex Avance CS2 Anesthesia Work Station Using Low Flow Anesthesia with Isoflurane, Sevoflurane, and Desflurane

Introduction: Gas Man® is a computer simulation program used for understanding the pharmacokinetics of volatile agents.On entering the patient details, fresh gas flow (FGF), volatile anesthetic concentration, and ventilatory details, it can predict the end-tidal concentration of volatile agents.ICOLLECT software is available for collection of real-time data from the workstation as well as hemodynamic parameters as it functions as a multichannel monitor.It is an electronic anesthetic record.We have used both these computer-based programs to study low flow anesthesia (LFA) in clinical practice.Aims: The primary purpose of this study was to compare the expired volatile anesthetic concentrations predicted by the Gas Man® simulation model with those actually occurring during general anesthesia (GA) using isoflurane, sevoflurane or desflurane in clinical practice using low FGF.Material and methods: Study area-the study was conducted in the Department of Anesthesiology, CARE Hospital, Hyderabad, Telangana, India.Study population-all patients who are posted for surgery under GA between the age groups 18-65 years, of either sex, and those belonging to the American Society of Anesthesiologists physical status I-II will constitute the study population.Sample size-a total of 30 patients undergoing GA with isoflurane, sevoflurane, and desflurane have undergone the validation trial using LFA.Our sample size calculation is based on a similar validation study.Study design-observational. Study duration-the proposed study was conducted over a period of 1 month (September 2016).Data collection techniques and tools-we collected relevant data directly from the Datex CS2 workstation via the ICOLLECT software for 30 anesthetics (isoflurane, sevoflurane, and desflurane) during the maintenance phase employing LFA.The measured concentration of volatile agent as well as the calculated concentration obtained by the Gas Man® equation were tabulated for each patient at 5-minute intervals.The performance error (PE), divergence, median predictive error, and wobble were determined for all three agents using the actual measured concentration end tidal agent against the predicted concentration.The statistics used for predicting the accuracy of volatile anesthetics uptake have been described by Varvel et al.Their model is based on those described for intravenous drug delivery systems.Multiple studies have validated this as a reliable model for predicting the accuracy of volatile anesthetics too.We calculated the median absolute performance error (MDAPE) median predictive error (MDPE) divergence, and wobble from the PE for all our cases.We calculated the MDAPE, MDPE, divergence, and wobble from the PE for all our cases.Results: Mann-Whitney U test done for each study group demonstrated that there was no statistically significant difference between the median measured end-tidal concentrations of volatile agents versus that predicted by the Gas Man® anesthesia simulator.The three groups were similar with respect to the measured and predicted end-tidal concentration of the anesthetic agent.Kruskal-Wallis test was undertaken to study the intergroup variability with respect to measured and predicted end-tidal concentration of volatile agents.We obtained a p-value of <0.01, confirms a statistically significant difference between the three groups.This is expected as the minimum alveolar concentration (MAC) requirements of the three agents studied are different.Discussion: In spite of the oversimplification of volatile kinetics, the Gas Man® simulation is an accurate predictor of the actual volatile agent's end-tidal concentrations achieved during LFA.It can serve as a useful educational tool for the implementation of LFA.Conclusion: There is good correlation between measured and predicted end-tidal concentrations of all three volatile anesthetics during LFA.