THE OPTIMAL INTRAVENOUS DOSE OF MIDAZOLAM AFTER INTRAVENOUS KETAMINE IN HEALTHY AWAKE CATS

The effects of intravenous administration of variable-dose midazolam ( 0, 0.05, 0.075, 0.1, 0.3 and 0.5 mg/kg) and ketamine (3 mg/kg) were st udied in twenty-four healthy unmedicated cats from time of administrat ion until full recovery. End-points were chosen to determine the optim al dose to allow a short period of restraint without noxious stimuli, a short period of restraint with noxious stimuli and endotracheal intu bation. Recovery characteristics, as well as undesirable behaviours ob served during recovery, were also recorded. The dose of midazolam to a chieve lateral recumbency with head down was found to be 0.016 mg/kg i n 50% of the population (ED50) and 0.054 mg/kg in 95% (ED95) of the po pulation. A midazolam dose of 0.286 mg/kg was required to prevent cons cious perception of a stimulus to the ulnar nerve in 50% of the popula tion and 0.652 mg/kg in 95% of the population The EB50 and ED95 Of mid azolam required to prevent swallowing in response to a laryngoscope pl aced on the back of the tongue were found to be 0.265 mg/kg and 0.583 mg/kg, respectively. The ED50 doses of 0.265 mg/kg for intubation and 0.286 mg/kg for restraint with noxious stimulation were close to the t ested dose of 0.3 mg/kg. At that dose, the lack of responses lasted 3. 67 +/- 2.27 min for laryngoscope and 2.50 +/- 2.20 min for ulnar nerve stimulation, with recovery to walking with ataxia taking 41.50 +/- 15 .18 min and complete recovery taking 3.6 +/- 1.3 h. The predominant be havioural pattern during recovery was found to be normal, but some cat s also exhibited abnormal behavioural patterns. Nine of the twelve cat s exhibited an abnormal arousal state, with 4 being restless and 5 bei ng sedated. Seven of the twelve cats exhibited an abnormal behaviour w hen approached, with three of the cats being more difficult to approac h and four of the cats being easier to approach. Eight of the twelve c ats exhibited an abnormal behavioural pattern when restrained, with th e cats equally divided between more difficult and easier to restrain. Five of the twelve cats vocalized more during the recovery. The ED50 O f 0.042 mg/kg to induce chemical restraint without a noxious stimulus is close to the tested dose of 0.05 mg/kg. At that dose, cats remained lateral with head down for 5.49 +/- 4.02 min, took 25.96 +/- 5.77 min to walk with ataxia and 1.7 +/- 0.4 h for complete recovery. The pred ominant behavioural patterns during recovery were normal, with several cats exhibiting some abnormal patterns. Two cats were sedated, one ca t was more difficult to approach, one cat was easier to restrain and t hree cats were more vocal.