VN March 2023

Vetnews | March 2023 9 Regardless of posture, the rhinoceroses were substantially hypoxemic and hypercapnic; no individual rhinoceros had P a O 2 .47 mm Hg or P a CO 2 ,50 mmHg (Table 2). Two of 12 rhinoceroses in lateral recumbency had pHa.7.35, whereas five of 12 suspended animals had pHa.7.35. Base excess was in the range of 7 to 2 mmol/L and lactate was between 0.9 and 4.8 mmol/L. When rhinoceros were suspended by their feet, there were significant differences in P a O 2 , S a O 2 , pH a , P a CO 2 , P( a-E´ )CO 2 , VD/VT, and P a O 2 when compared to animals in lateral recumbency (Tables 2, 3). In suspended animals, mean P A O 2 was 4 mm Hg greater, mean S a O 2 was 8% greater, and mean pH a was greater compared with lateral recumbency(7.34 vs. 7.32; Table 2). The mean P a CO 2 was 3 mm Hg less when rhinoceroses were suspended (Table 2) than it was when they were in lateral recumbency. Mean P( a-E´ )CO 2 and VD/VT were 4 mm Hg and 4% less, respectively, when the animals were suspended (Table 3) compared with lateral recumbency. Mean P A O 2 was 4 mm Hg greater when the rhinoceroses were suspended (Table 3). Base excess, lactate, VT, fR, VE, VCO 2 , and P( A-a )O 2 were not significantly different between the two treatments (Tables 2, 3). TABLE 3. Mean (SD) values from12 immobilizedwild black rhinoceroses (Diceros bicornis) inNamibia during investigations comparing the pulmonary physiology of lateral position with aerial suspension by the feet. Animals were in lateral recumbency or suspended by the feet for approximately 10min before data collection. Each rhinoceros received both treatments sequentially, in randomorder. The alpha value for comparisons was 0.05. a a P E ´ CO 2 = end-tidal pressure of carbon dioxide; P( a=E ´ )CO 2 = arterial to end-tidal carbon dioxide pressure difference; VCO 2 = rate of carbon dioxide production; PAO 2 = alveolar oxygen pressure; P( A=a )O 2 = alveolar to arterial oxygen pressure difference. * = significantly different. Only P a CO 2 and P A O 2 were significantly affected by the order of treatment. Mean P a CO 2 was 6 mm Hg greater and mean P A O 2 was 8 mm Hg less in the animals that were in lateral recumbency first compared with those when they were in lateral recumbency second; no such effects of treatment order were apparent in the animals when they were suspended by the feet (Table 4). Mean time in posture before data collection was 14 min longer for those animals that were in lateral recumbency first as compared with those that were in lateral recumbency second; no such effect of treatment order was apparent in the animals when they were suspended (Table 4). When suspension by the feet was followed by a move to the lateral position, the mean P a CO 2 increased, while mean P a O 2 and pH a declined, in five of six animals, whereas a move from lateral recumbency to suspension was followed by corresponding changes in the opposite direction in four of six animals. Leading Article Measurement Lateral recumbency (n = 12) Suspended by the feet (n = 12) P Tidal volume (mL/kg) 11(2.9) 11 (1.7) 0.783 Breathing rate (breaths/min) 5.6 (1.2) 5.5 (1.1) 0.792 Minute ventilation (mL/kg/min) 59 (2.6) 59 (1.2) 0.803 P E ´ CO 2 (mm Hg) 39 (5.5) 39 (4.7) 0.626 P( a=E ´ )CO 2 (mm Hg) 16 (3.1) 12 (3.2) 0.002* Enghoff dead space fraction (%) 56 (4) 52 (4) 0.005* VCO 2 (mL/kg/min) 2.3 (0.44) 2.4 (0.40) 0.614 P A O 2 (mm Hg) 53 (6.6) 57 (5.3) 0.017* P( A=a )O 2 (mm Hg) 15 (5.3) 15 (2.6) 0.927 >>> 10