Performance of computer simulated inhalational anesthetic uptake model in comparison with real time isoflurane concentration

Gas Man software was developed to enhance our understanding of the pharmacokinetics of inhalational anaesthetics. To date the Gas Man software has not been validated in humans. In this study we compared the Gas Man software with real time measured end tidal isoflurane concentrations while using a semi closed circle system in anesthetised patients. Thirty-four ASA I and II patients 18–60 years of age were selected for the study. After a standardized induction anesthesia was maintained with N₂O + O₂ mixture and isoflurane using the circle system. The fresh gas flow or dial setting of Isoflurane vaporizer were changed at random. The inspired and end-tidal concentration values of isoflurane measured at 1 min intervals were retrieved from the patient monitor. Real time anesthetic settings for the patient were simultaneously simulated in the Gas Man software to generate the inspired and end-tidal concentration of isoflurane values at every minute for comparison. Varvel’s criteria have been used to assess this model. The median absolute performance error was 9.39 %, median performance error was −5.30 %, wobble was 5.16 %, and divergence was −1.82 %. All criteria were within limits of the acceptable performance of the model. The end-tidal concentration values of isoflurane in real patients are very close to those predicted by Gas Man software. The pharmocokinetics of inhalational anesthetic administration in patients can be taught accurately using Gas Man technology. This technology may also help in developing different kinetic models of inhalational agents in the body.