Abstract
A number of design modifications have been made to an extraction system for use with inhalation anaesthesia techniques in rats and other small laboratory animals. These changes necessitated a re-evaluation of the effectiveness of this equipment in limiting the operator's exposure to the anaesthetic vapours used. With a given fresh gas flow. the halothane vapour concentration in the operator's breathing zone was dependent on the design of the oronasal mask. With the optimum configuration the atmospheric concentration of halothane was less than 1 ppm.