THORACIC EPIDURAL BLOCK ATTENUATES CARDIOVASCULAR-RESPONSE TO APNEA IN RABBITS

Purpose: Apnea is one of the potential complications during anaesthesi a. If sympathetic nerve activity is blocked by epidural anaesthesia, c irculatory responses to apnea might change. Our objective was to asses s the potential modifying effects of epidural anaesthesia on the cardi ovascular responses to apnea in the animals. Methods: Twenty rabbits a naesthetised with pentobarbital (25 mg . kg(-1) iv, 8 mg . kg(-1) hr(- 1)) and pacuronium bromide (0.2 mg . kg(-1) hr(-1) iv) were randomly a ssigned to one of two groups: control (n = 10) and epidural (n = 10). In the control group, 0.6 ml saline, and in the epidural group, 0.6 ml lidocaine 1% was injected into the epidural space respectively. After mechanical ventilation with FIO2 0.4; apnea was induced by disconnect ing the anaesthetic circuit from the endotracheal tube, and mean arter ial pressure (MAP), heart rate (HR), and-time to cardiac arrest were m easured. Results: Before apnea MAP was lower in the epidural than in t he control group (73 +/- 10 vs 91 +/- 10 mmHg, P < 0.05). Heart rate w as not different between groups (264 +/- 36 vs 266 +/- 24 bpm). Mean a rterial pressure increased in the control group after apnea, but not i n the epidural group. The time to cardiac arrest was less in the epidu ral group than in the control group (420 +/- 67 vs 520 +/- 61 sec, P < 0.05). Heart rate decreased markedly after apnea in the control group whereas it decreased gradually in the epidural group. Conclusion: Tho racic epidural anesthesia attenuated cardiovascular response to apnea and reduced the time to cardiac arrest.