In sheep, alpha(2)-agonists can induce severe hypoxaemia. In goats, reports on changes in oxygenation are inconsistent. The aim of this study was to compare the cardiopulmonary effects of dexmedetomidine in six goats and four sheep anaesthetised with sevoflurane and maintained at approximately 1 minimal alveolar concentration. The animals were ventilated mechanically and held in an upright position to minimise the influence of positioning on pulmonary function. After baseline cardiopulmonary measures, 2 microg/kg dexmedetomidine was injected intravenously over one minute, and measurements were made for 120 minutes. In both species, respiratory resistance, alveolar dead space and shunt fraction increased and thoracic compliance decreased significantly; arterial, pulmonary arterial, pulmonary capillary wedge and central venous pressures increased and heart rate and cardiac output decreased significantly. Arterial oxygen tension decreased significantly, with no significant difference between the goats and sheep. Wide interindividual differences were observed in both the goats (mean [sd] 144 [149.1] mmHg, range 54.8 to 443.7 mmHg) and sheep (mean [sd] 129.8 [132.1] mmHg, range 33.7 to 352.8 mmHg), but the cardiovascular and respiratory changes were similar in the two species.
