Respiratory and circulatory parameters of African elephants (Loxodonta africana) anaesthetised with etorphine and azaperone

Abstract

Respiratory rate, heart rate, blood-gas tensions (PO2 and PCO2) and pH of arterial (a) and peripheral venous (v) blood, concentration of haemoglobin in arterial blood (Hb), saturation of arterial haemoglobin with oxygen and the end-expiratory concentration of oxygen were measured in 22 juvenile African elephants (Loxodonta africana) anaesthetised with etorphine and azaperone during a period of 35-65 minutes after they had assumed lateral recumbency. Based on these parameters the alveolar-arterial and arterial-peripheral venous differences of PO2 [P(A-a)O2 and P(a-v)O2 respectively] and oxygen content of arterial blood (CaO2) were calculated. Elephants with body mass of < or = 600 kg showed statistically significant changes in the following parameters, compared with elephants with a body mass of more than 600 kg (x +/- SD): PaO2 (64 +/- 11 versus 82 +/- 8 mmHg), P(a-v)O2 (9 +/- 5 versus 22 +/- 9 mmHg), P(A-a)O2(37 +/- 16 versus 15 +/- 8 mmHg) and Hb (148 +/- 20 versus 130 +/- 10 g/l) (p < 0.05). These findings suggested a tendency towards impaired oxygen exchange in the lungs, reduced peripheral extraction of oxygen and elevated oxygen-carrying capacity of arterial blood in smaller elephants. These changes were theoretically attributed to the respiratory-depressant and sympathomimetic effects of higher dosages of etorphine used in the smaller elephants to maintain a clinically acceptable anaesthetic plane. Individual elephants spent 35-150 minutes under anaesthesia and all recovered uneventfully after reversal of etorphine with diprenorphine.