Evaluation of certain tranquillisers and sedative premedications on the safety index of volatile anaesthetics.

Safety index (S.I.) of ether, chloroform and halothane was determined in mice following premedication with chloral hydrate, phenobarbitone, diazepam and trifluoperazine given alone or in combination with atropine or hyoscine. The S.I. of ether was significantly raised by chloral hydrate and phenobarbitone when combined with atropine while trifluoperazine in combination with atropine or hyoscine lowered it. The S.I. of chloroform and halothane was raised by chloral hydrate, phenobarbitone and diazepam. The S.I. raising effects were augmented in chloroform anaesthesia and reduced in cases of halothane (except diazepam-hyoscine) when these premedications were combined with atropine or hyoscine.