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 isoflurane induction in five New Zealand White (NZW) rabbits. Slow induction used stepwise increments in vapour setting of 2% for desflurane and 0.5% for isoflurane at 30 s intervals. All animals were anaesthetized using each technique according to a randomized block design with one week between treatments. Observations were made of the quality of induction (any struggling or periods of apnoea) and the latency to, and the duration of loss of the righting and toe pinch reflexes recorded. Changes in respiratory rate, arterial blood gas and cardiovascular parameters were also recorded. Induction and recovery times were shorter with rapid desflurane induction in comparison to isoflurane (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 significant degree of bradycardia, hypercapnia and hypoxaemia occurred with both techniques, but these and the subsequent effects of rapid desflurane administration were less severe than with isoflurane. Slow induction with desflurane was tolerated best, with little or no deleterious behavioural or physiological effects, however excessively prolonged induction times (loss of righting reflex 337+/-160 s) limits the application of this method. Desflurane, administered rapidly, appears to be a more suitable agent than isoflurane. However, as with isoflurane, anaesthesia should only be induced following oxygen supplementation.