ANESTHETIC POTENCY AND CARDIOPULMONARY EFFECTS OF ENFLURANE, HALOTHANE, AND ISOFLURANE IN GOATS

Anesthetic requirements, as defined by the minimum alveolar anesthetic concentration (MAC) that prevents gross, purposeful movement in 50% o f animals, have not been determined in goats. Therefore, we determined anesthetic potency of enflurane (N = 6), halothane (N = 8), and isofl urane (N = 7) in goats by using the tail clamp and dew-claw clamp as t he noxious stimuli and then measured the cardiovascular and respirator y effects of these agents. The MAC was 2.0 +/- 0.4%, 1.3 +/- 0.1%, and 1.5 +/- 0.3% (mean +/- SD) for enflurane, halothane, and isoflurane, respectively. At 1 MAC, when ventilation was changed from controlled t o spontaneous, blood pressure decreased in goats anesthetized with iso flurane (98 +/- 17 to 78 +/- 13 mm Hg) and halothane (95 +/- 10 to 83 +/- 14 mm Hg) but did not significantly change in goats anesthetized w ith enflurane; heart rate increased in goats anesthetized with halotha ne (117 +/- 12 to 127 +/- 10 beats/min) but was not significantly diff erent in goats anesthetized with enflurane or isoflurane; and cardiac output increased in goats anesthetized with enflurane (5.70 +/- 1.23 t o 7.05 +/- 2.02 liters/min) and halothane (6.14 +/- 0.94 to 7.91 +/- 2 .45 liters/min) but not with isoflurane. During spontaneous breathing, respiratory depression was manifested by apnea in two animals and an elevated PaCO2: 57 +/- 15 mm Hg, 55 +/- 13 mm Hg, and 59 +/- 14 mm Hg, respectively, for enflurane, halothane, and isoflurane. Minute ventil ation during spontaneous breathing was approximately 50% of controlled ventilation for each anesthetic agent. We conclude that anesthetic re quirements in goats are similar to those in other species; enflurane, halothane, and isoflurane are well tolerated during controlled ventila tion; and respiratory depression makes these drugs less attractive dur ing spontaneous breathing.