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

Abstract

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 (PaO2 = 27 ± 7 mmHg [mean ± SD]), hypercapnia (PaCO2 = 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 PaO2 (60 ± 3 mmHg, F (3,21) =151.9, p < 0.001), PaCO2 (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 (PaO2 = 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.

Figure 1

Values are respiratory rate (A), partial pressure of arterial carbon dioxide (P _a CO ₂ ) (B), partial pressure of arterial oxygen (P _a O ₂ ) (C), and arterial pH (D) (means, SD, n =8) of rhinoceros given intravenous butorphanol, intravenous butorphanol + oxygen insufflation, oxygen insufflation and intravenous sterile water (control) 6 minutes after the rhinoceros became laterally recumbent. Arrow at 6 minutes indicates time at which the intervention was given. Arrow at 21 minutes indicates the end of lateral recumbency. Dotted lines indicate average normal values in standing, unsedated white rhinoceros [12]. The brackets show when treatments differed from each other with letters indicating the treatment comparisons as follows: a = butorphanol vs. control; b = butorphanol vs. butorphanol + oxygen; c = butorphanol vs. oxygen; d = oxygen vs. control; e = oxygen vs. butorphanol + oxygen and f = butorphanol + oxygen vs. control.

Figure 2

Areas under the response curves. Comparisons between the calculated values of the area under the response curves for respiratory rate (A), partial pressure of arterial carbon dioxide (P_aCO₂) (B), partial pressure of arterial oxygen (P_aO₂) (C) and arterial pH (D). The asterix (*) indicates when the treatments butorphanol (But), butorphanol + oxygen (But + O₂) or oxygen only (O₂) differ significantly from the control, with the number of asterixes indicating the level of significance (*p <0.05, **p <0.01 and ***p <0.001).