VN March 2023

Vetnews | March 2023 7 These drugs may contribute to serious or fatal complications including hypoventilation, hypoxemia, hypercapnea, hypertension, and acidemia (Kock et al. 1990; Morkel et al. 2010; Fahlman et al. 2016). To facilitate loading for ground transportation, the opioids used for capture are usually partially antagonized, decreasing their adverse side-effects (Miller et al. 2013; Haw et al. 2014). However, safe aerial suspension under a helicopter requires complete immobility and, therefore, partial opioid antagonism is not routinely employed in black rhinoceroses that are air-lifted. Furthermore, posture under anesthesia affects pulmonary and cardiovascular function (Steffey et al. 1990). Immobilized black rhinoceros in sternal recumbency have significantly greater median arterial oxygen pressure (P a O 2 ) than in lateral recumbency (56 mm Hg vs. 41 mm Hg, respectively), although alveolar ventilation is similar in the two postures (Radcliffe et al. 2014). Unfortunately, no physiological data are available to assess the risks for airlifted rhinoceroses suspended by their feet. A white rhinoceros (Ceratotherium simum) positioned in dorsal recumbency for colic surgery experienced more profound hypoxemia than did rhinoceroses in lateral recumbency (Valverde et al. 2010). Anesthetized horses (Equus caballus), which are closely related phylogenetically to rhinoceroses, have more venous admixture and lower arterial oxygen tension in dorsal recumbency (but not suspended) than in lateral recumbency (Nyman and Hedenstierna 1989). Although objective measurements are not available, horses suspended from a hoist by their feet appear by visual inspection to be dyspneic because the abdominal contents restrict diaphragm movement and, perhaps, are displaced cranially, thus compressing the lungs and other thoracic organs. Consequently, suspending recently captured black rhinoceroses by their feet for aerial transportation might compromise their pulmonary function at a time when they are already hypoxemic and hypercapnic. Because there is a paucity of physiological information on airlifted rhinoceros, the first aim of this study was to collect measurements on black rhinoceroses suspended by their feet from a crane to mimic the position that they would be in while being transported under a helicopter. Specifically, we hypothesized that immobilized black rhinoceroses suspended by their feet would have higher arterial carbon dioxide pressure (P a CO 2 ) and lower P a O 2 than they would lying on the ground in lateral recumbency. White rhinoceroses immobilized with etorphine have oxygen consumption and carbon dioxide production (VCO 2 ) greater than might be expected (Buss et al. 2018); this could be caused by increased skeletal muscle activity (de Lange et al. 2017). It is possible that this hypermetabolic state contributes to the hypoxemia, hypercapnea, hypertension, and acidemia observed when white rhinoceroses are immobilized with etorphine. No similar metabolic data are available for black rhinoceroses. However, the technique used for measuring ventilation in the field allows calculation of the VCO 2 . Because a hypermetabolic state is reported in white rhinoceroses after etorphine (Buss et al. 2018; Boesch 2020), the second aim of this study was to assess whether black rhinoceroses immobilized with etorphine and azaperone were in a similar hypermetabolic state. To test this, we hypothesized that immobilized black rhinoceroses would have a greater VCO 2 than that predicted allometrically. Leading Article >>> 8 Figure 2 Hanging posture of a black rhinoceros (Diceros bicornis) using a crane on a flatbed truck to simulate aerial suspension under a helicopter in Namibia.