Anestéziológia a intenzívna medicína 1/2016

When reducing the inflow of fresh gas in the LFA?

Goal:To elucidate the theoretical principles of fresh gas flow (Qfgf) regulation based on the changes of anaesthetic concentration and consumption. To investigate the usefulness of consumption changes for the Qfgf regulation during the low flow anaesthesia. Material and methods:50 randomly chosen patients underwent coronary artery bypass grafting surgery using low flow anaesthesia. After the i. v. anaesthetic induction we measured changes of Sevoflurane concentration and consumption at Qfgf 5 l/min. for the first 5 minutes and then at Qfgf 2 l/min. for the next 15 minutes. We recorded and evaluated changes of anaesthetic (AA) concentration and consumption in relationship to stability of mean alveolar concentration (MAC) and to a possibility of transition from high flow to low flow anaesthesia. Results:We found that mainly during the introduction of inhalation anaesthesia it is absolutely impossible to estimate a right moment when to transit from high flow to low flow based on the anaesthetic concentration changes. Oppositely by following the consumption changes we showed that once the anaesthetic consumption dropped down to 20 – 25 % of the entry value it was suitable and safe to reduce the Qfgf to low flow values. Conclusion:Using measures of delivered and consumed anaesthetic gas and a decrease of anaesthetic consumption we concluded that it is crucial to follow the anaesthetic amount (gr) changes and its percentage decrease in time to correctly control Qfgf and AA concentration. Once the anaesthetic consumption falls down to 20 – 25 % of entry value it is reasonable and safe to decrease Qfgf to around 1 l/min or less.

Keywords: low flow anaesthesia, fresh gas flow, AA consumption, AA concentration