Butorphanol with oxygen insufflation corrects etorphine-induced hypoxaemia in chemically immobilized white rhinoceros (Ceratotherium simum)

BACKGROUND: Opioid-induced immobilization is associated with severe respiratory depression in the white rhinoceros. We evaluated the efficacy of butorphanol and oxygen insufflation in alleviating opioid-induced respiratory depression in eight boma-managed rhinoceros. RESULTS: Chemical immobilization with etorphine, azaperone and hyaluronidase, as per standard procedure for the white rhinoceros, caused severe respiratory depression with hypoxaemia (P(a)O(2) = 27 ± 7 mmHg [mean ± SD]), hypercapnia (P(a)CO(2) = 82 ± 6 mmHg) and acidosis (pH =7.26 ± 0.02) in the control trial at 5 min. Compared to pre-intervention values, butorphanol administration (without oxygen) improved the P(a)O(2) (60 ± 3 mmHg, F((3,21)) =151.9, p <0.001), P(a)CO(2) (67 ± 4 mmHg, F((3,21)) =22.57, p <0.001) and pH (7.31 ± 0.06, F((3,21)) =27.60, p <0.001), while oxygen insufflation alone exacerbated the hypercapnia (123 ± 20 mmHg, F((3,21)) =50.13, p <0.001) and acidosis (7.12 ± 0.07, F((3,21)) =110.6, p <0.001). Surprisingly, butorphanol combined with oxygen fully corrected the opioid-induced hypoxaemia (P(a)O(2) = 155 ± 53 mmHg) and reduced the hypercapnia over the whole immobilization period (p <0.05, areas under the curves) compared to the control trial. However, this intervention (butorphanol + oxygen) did not have any effect on the arterial pH. CONCLUSIONS: Oxygen insufflation combined with a single intravenous dose of butorphanol improved the immobilization quality of boma-managed white rhinoceros by correcting the opioid-induced hypoxaemia, but did not completely reverse all components of respiratory depression. The efficacy of this intervention in reducing respiratory depression in field-captured animals remains to be determined.