EFFECTS OF A SUPPLEMENTAL ETORPHINE DOSE ON PULMONARY ARTERY PRESSURE AND CARDIAC OUTPUT IN IMMOBILIZED, BOMA-HABITUATED WHITE RHINOCEROS ( CERATOTHERIUM SIMUM): A PRELIMINARY STUDY.

The effects of etorphine on the pulmonary vascular system of white rhinoceros ( Ceratotherium simum) have not been described and could play a role in the severe hypoxemia that develops after immobilization with etorphine-based drug combinations. Characterization of these effects requires measurement of pulmonary vascular pressures and cardiac output (CO). To refine a technique for pulmonary arterial catheterization, five boma-habituated white rhinoceros (three females and two males weighing 1,012-1,572 kg) were immobilized by remote injection with etorphine plus azaperone followed by butorphanol. This afforded the opportunity to perform a pilot study and acquire preliminary measurements of pulmonary arterial pressure (PAP) and CO before and after supplemental etorphine given intravenously. Ultrasonographic guidance was used to insert a sheath introducer into a linguofacial branch of a jugular vein. A 160-cm-long pulmonary artery catheter with a balloon and thermistor was then passed through the introducer and positioned with its tip in the pulmonary artery. It was not long enough to permit wedging for measurement of pulmonary artery occlusion pressure. Mean PAP was 35 mm Hg (minimum, maximum 32, 47 mm Hg) and increased ( P = 0.031) by 83% (28, 106%) after supplemental etorphine. Thermodilution CO was 120 L/min (92, 145 L/min) and increased 27% (3, 43%) ( P = 0.031). Heart rate was 100 (88, 112) beats/min and increased 20% (4, 45%) ( P = 0.031), whereas arterial partial pressure of oxygen was 35 mm Hg (30, 94 mm Hg) and decreased 47% (20, 72%) ( P = 0.031). The cardiovascular observations could result from etorphine-induced generalized sympathetic outflow, as has been reported in horses. Further studies of etorphine in isolation are needed to test this suggestion and to discern how the changes in pulmonary vascular pressures and blood flow might relate to hypoxemia in etorphine-immobilized white rhinoceros.