Water vapour in a closed anaesthesia circuit reduces degradation/adsorption of halothane by dried soda lime

Dry lime causes a loss of volatile anaesthetics by degrading and adsorbing them. Degradation produces toxic substances and heat. Rehydration of lime stops degradation. If humidified breathing gases rehydrate lime, closed anaesthesia-circuits may reduce the loss of anaesthetics. To test this hypothesis we ventilated a reservoir bag with PhysioFlex(R)-devices using fresh (F) and dried (D) soda lime both in the presence (+H) and absence (-H) of halothane. We measured halothane delivery, humidity, temperature, and lime weight. Halothane was lost For 13 min in D+H. Humidity increased steeper with fresh lime, whereas absorbent weight increased more with dried lime; halothane increased both variables (F+H: 99%, 8 g; F-H: 93%, 6 g; D+H: 58%, 17 g; D-H: 24%, 15 g). Surprisingly, temperature remained constant, probably because of the high gas flow (70 litres min(-1)) generated inside the Physioflex(R). These findings indicate rehydration of dried lime by humid gases and a rapid cessation of the loss of halothane in the PhysioFlex(R).