PULMONARY DEAD SPACE IN FREE-RANGING IMMOBILIZED BLACK RHINOCEROSES (DICEROS BICORNIS) IN NAMIBIA

Abstract

It was observed previously that end-expired carbon dioxide (P(E)CO2) decreased when immobilized black rhinoceroses (Diceros bicornis) were moved from sternal to lateral recumbency. These experiments were designed to test whether greater alveolar ventilation or greater pulmonary dead space in lateral recumbency explains this postural difference in P(E)CO2. Twenty-one (9 male, 12 female; 15 [3.5-26] yr old) wild black rhinoceroses were immobilized with etorphine and azaperone and positioned in either sternal or lateral recumbency. All rhinoceroses were hypoxemic and had lactic and respiratory acidemia. The animals in lateral recumbency were more acidemic, had higher lactate, and lower arterial oxygen that those in sternal recumbency; however, arterial carbon dioxide was similar between groups. Both P(E)CO2 and mixed expired carbon dioxide pressure were lower in lateral than sternal recumbency. Although there was no difference in tidal volume or arterial carbon dioxide, both the breathing rate and minute ventilation were greater in lateral recumbency. The physiologic dead space ratio and dead space volume were approximately two times larger in lateral recumbency; hence, the decrease in P(E)CO2 in lateral recumbency can be attributed to increased dead space ventilation not increased alveolar ventilation. Positioning immobilized rhinoceroses in lateral recumbency does not confer any advantage over sternal in terms of ventilation, and the increase in minute ventilation in lateral recumbency can be considered an energetic waste. Although arterial oxygen was superior in sternal recumbency, further studies that measure oxygen delivery (e.g., to the muscles of locomotion) are warranted before advice regarding the optimal position for immobilized rhinoceroses can be given with confidence.

Cardiopulmonary Parameters and Arterial Blood Gases During Etorphine-Medetomidine-Midazolam Immobilization in Free-Ranging Black Rhinoceroses (Diceros bicornis) Undergoing Electro-Ejaculation—A Preliminary Study

“…Immobilization with etorphine-medetomidine-midazolam resulted in short induction times similar to those previously reported in free-ranging black rhinoceroses immobilized with other etorphine-combinations ( 6 , 8 , 9 ) and uneventful recoveries. No muscle tremors were observed and lac was normal in all but one animals.…”

“…Potent opioids result in rapid induction times and therefore a reduced risk of capture myopathy and injury ( 6 , 7 ). However, they are associated with muscle rigidity, respiratory depression, hypertension, acidemia and hyperlactatemia ( 6 , 8 , 9 ). Azaperone is the most commonly added tranquilizer, but is reported to inhibit semen emission ( 10 ).…”

Pulmonary gas exchange and acid–base status during immobilisation of black rhinoceroses (<i>Diceros bicornis</i>) in Zimbabwe

“…In the present study, the lower arterial oxygenation measured in black rhinoceroses during lateral compared to sternal recumbency is in line with previous reports in black rhinoceroses, white rhinoceroses and horses (Gleed & Dobson 1988 ; Radcliffe et al . 2014 ; Wenger et al . 2007 ).…”

“…A recent study demonstrated that black rhinoceroses immobilised with etorphine and azaperone experienced more severe hypoxaemia and lactic acidaemia during lateral compared to sternal recumbency (Radcliffe et al . 2014 ).…”

“…2001 ), and in free-ranging black rhinoceroses immobilised with etorphine and azaperone (Radcliffe et al . 2014 ). The principal aim of this study was to evaluate pulmonary gas exchange and acid–base status in black rhinoceroses immobilised with drug combinations including an opioid, azaperone and an α 2 -adrenoceptor agonist.…”