LIDOCAINE PROLONGS THE SAFE DURATION OF CIRCULATORY ARREST DURING DEEP HYPOTHERMIA IN DOGS

Purpose: To test the hypothesis that lidocaine prolongs the safe perio d of circulatory arrest during deep hypothermia. Methods: Sixteen dogs were subjected to cooling, first surface cooling to 30 degrees C and then core cooling to 20 degrees C rectal temperature). The circulation was then stopped for 90 min. In the lidocaine group, 4 mg.kg(-1) lido caine was injected into the oxygenator two minutes before circulatory arrest and 2 mg.kg(-1) at the beginning of reperfusion and rewarming. The control group received equivalent volumes of normal saline. Post-o peratively, using a neurological deficit scoring system (maximum defic it score - 100; minimum - zero indicating that no scored deficit could be detected). Neurological function was evaluated hourly for six hour s and then daily for one week, the pharmacokinetic parameters were cal culated using one compartment model. Results: On the seventh day, the neurological deficit score and overall performance were better in the lidocaine (0.83 +/- 2.04) than in the control group (8.33 +/- 4.08 P < 0.05). During the experiment, the base excess values were also better in the lidocaine than in the control group (at 30 min reperfusion :-4 .24 +/- 1.30 vs -8.20 +/- 2.82 P < 0.01, at 60 min reperfusion was -3. 34 +/- 1.87 vs -7.52 +/- 2.40 (P < 0.01). On the eighth day the extent of pathological changes were milder in the lidocaine group than that in the control group. The elimination half life of lidocaine was 40.44 +/- 7.99 during hypothermia and 2.01 +/- 4.56 during rewarming. Concl usions: In dogs lidocaine prolongs the safe duration of circulatory ar rest during hypothermia.