title: Water vapour in a closed anaesthesia circuit reduces degradation/adsorption of halothane by dried soda lime.
abstract: 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-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. These findings indicate rehydration of dried lime by humid gases and a rapid cessation of the loss of halothane in the PhysioFlex.
authors.affiliation: Department of Experimental and Clinical Anaesthesiology, Heinrich-Heine-University, Duesseldorf, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Schindler
authors.forename: M
authors.initials: M
authors.lastname: Vorweg
authors.forename: T W
authors.initials: TW
authors.lastname: Scheeren
authors.forename: M
authors.initials: M
authors.lastname: Doehn
mesh_terms: D000327:Adsorption; D000764:Anesthesia, Closed-Circuit; D018685:Anesthetics, Inhalation / Q000737:chemistry*; D017610:Calcium Compounds / Q000737:chemistry*; D006221:Halothane / Q000737:chemistry*; D006801:Humans; D006813:Humidity; D010087:Oxides / Q000737:chemistry*; D012972:Sodium Hydroxide / Q000737:chemistry*; D014867:Water
chemical_list: D018685:Anesthetics, Inhalation; D017610:Calcium Compounds; D010087:Oxides; D014867:Water; C004569:soda lime; D012972:Sodium Hydroxide; D006221:Halothane