Induction of anaesthesia with desflurane and isoflurane in the rabbit

The characteristics of two techniques of face-mask induction of desflurane anaesthesia (rapid or slow) were compared with the effects of slow isoflura ne induction in five New Zealand White (NZW) rabbits. Slow induction used s tepwise increments in vapour setting of 2% for desflurane and 0.5% for isof lurane at 30 s intervals. All animals were anaesthetized using each techniq ue according to a randomized block design with one week between treatments. Observations were made of the quality of induction (any struggling or peri ods of apnoea) and the latency to, and the duration of loss of the righting and toe pinch reflexes recorded. Changes in respiratory rate, arterial blo od gas and cardiovascular parameters were also recorded. Induction and reco very times were shorter with rapid desflurane induction in comparison to is oflurane (loss of righting reflex: 139 +/- 27 s cf. 205 +/- 48 s), but both techniques were associated with struggling and long periods of apnoea (>1 min) during the first 4 min after administration. During this period a sign ificant degree of bradycardia, hypercapnia and hypoxaemia occurred with bot h techniques, but these and the subsequent effects of rapid desflurane admi nistration were less severe than with isoflurane. Slow induction with desfl urane was tolerated best, with little or no deleterious behavioural or phys iological effects, however excessively prolonged induction times (loss of r ighting reflex 337 +/- 160 s) limits the application of this method. Desflu rane, administered rapidly, appears to be a more suitable agent than isoflu rane. However, as with isoflurane, anaesthesia should only be induced follo wing oxygen supplementation.