Evaluation of a scavenging system for use with inhalation anaesthesia techniques in rats

Summary A minimum fresh gas flow of I litre per minute per mask and an inspired concentration of 2-3% halothane was required to induce anaesthesia in rats in 1-2 min. Anaesthesia was maintained with an inspired concentration of 1·5-2% halothane. Arterial carbon dioxide concentration increased during anaesthesia and was not reduced by increasing the flow of fresh gas. Using the apparatus described here, halothane vapour concentration in the operator's breathing zone was 5 ppm. Prior to its introduction, levels of 250 ppm had been recorded in a poorly-ventilated animal room. Although it has been suggested that trace concentrations of anaesthetics may affect the psychomotor performance of operating theatre personnel (Bruce, Bach & Arbit, 1974), the balance of experimental evidence indicates that concentrations of halothane much higher than to ppm are required to produce detrimental effects (Smith & Shirley, 1978). A recent review of possible hazards in operating theatres concluded that the risk of spontaneous abortion appeared to be increased in association with anaesthetic practice (Spence & Knill-Jones, 1978). Although there is no direct evidence to implicate contamination by anaesthetics, it is sensible to take reasonable precautions to reduce that contamination. The system commonly used to anaesthetize rats with gaseous agents utilizes a continuous flow of a vapour mixture, delivered through a face mask. This invariably leads to a considerable escape of anaesthetic vapour into the operator's breathing zone. Our objective was to evaluate the effectiveness of a system designed to limit this atmospheric contamination to an acceptable and reasonable level.