Determination of the minimum alveolar concentration of isoflurane in donkeys

Abstract

OBJECTIVE To determine the minimum alveolar concentration (MAC) of isoflurane in donkeys and characterize recovery from anesthesia. ANIMALS 7 healthy castrated male adult donkeys. PROCEDURES Anesthesia was induced with propofol and maintained under mechanical ventilation with 1.3% isoflurane end-tidal concentration (ETiso). The MAC of isoflurane was determined after a 60-minute propofol washout period using the bracketing method. A continuous noxious electrical stimulation was applied to the oral mucosa for 1 minute or until the donkey moved. The ETiso was increased or decreased by 10% depending on the response, and MAC was defined as the average of 2 ETiso values allowing and preventing movement in response to stimulation. Arterial blood gases were measured during anesthesia and the recovery period. Unassisted recovery was timed, and a quality score was assigned from 1 (very poor) to 5 (excellent). RESULTS The mean dose of propofol required for induction was 3.0 ± 0.6 mg/kg. The MAC of isoflurane was 1.44 ± 0.13%. One donkey was excluded from the study because it was still responsive when stimulated at ETiso of 2.8%. Immediately after extubation, the median (range) partial pressure of oxygen in the arterial blood was 63 (minimum to maximum, 46 to 72) mm Hg and 3 donkeys were hypoxemic (partial pressure of arterial oxygen < 60 mm Hg). The median time to standing was 13 (7 to 38) minutes, while the recovery score was 3 (2 to 5). CLINICAL RELEVANCE The MAC of isoflurane in donkeys is similar to that reported in other species. Oxygen support should be provided to donkeys during recovery from isoflurane anesthesia to prevent hypoxemia.