Epidural anaesthetic effect of the 8% emulsified isoflurane: a study in rabbits

Studies have shown that local use of volatile anaesthetics produce local anaesthetic effects such as local infiltration anaesthesia (in rats and humans) and spinal anaesthesia (in dogs). However, there is still no report on the epidural anaesthetic effect of volatile anaesthetics. The aim of the present study was to evaluate the epidural anaesthetic effect of the 8% emulsified isoflurane in rabbits.

Forty rabbits chronically instrumented with an epidural catheter were randomly divided into four groups of 10 rabbits each. According to group assignment, rabbits received epidural administration of 8% emulsified isoflurane (v/v) 1 ml in the E-isoflurane group, 1% lidocaine 1 ml in the Lidocaine group, 30% lipid emulsion 1 ml in the Itralipid group, or normal saline 1 ml in the NS group. The sensory and motor functions and the state of consciousness were assessed at baseline and at predetermined regular intervals. Then, the rabbits were continuously observed for 2 weeks to examine the possible long-term neurological complications.

The sensory blockade onset time, motor blockade onset time, and motor blockade duration in the E-isoflurane group [1.4 (0.7), 1.6 (0.7), and 34 (10) min, respectively] were similar to those in the Lidocaine group [1.3 (0.5), 1.7 (0.8), and 38 (8), min, respectively]. The sensory blockade duration in the E-isoflurane group was longer than that in the Lidocaine group [68 (13) vs 49 (13) min, P<0.01]. No epidural anaesthetic effects occurred in the NS group and the Intralipid group. None of the rabbits showed an abnormal consciousness after the epidural drug administration. None of the rabbits showed any long-term neurological deficits during a 2 week observation.

The present study demonstrates that epidural administration of the 8% emulsified isoflurane produces completely a reversible epidural anaesthetic effect that does not affect the level of consciousness in rabbits.