Intranasal oxygen reverses hypoxaemia in immobilised free-ranging capybaras (Hydrochoerus hydrochaeris)

Abstract

Capybara (Hydrochoerus hydrochaeris) is the main host of tick-borne pathogens causing Brazilian spotted fever; therefore, controlling its population is essential, and this may require chemical restraint. We assessed the impact of chemical restraint protocols on the partial pressure of arterial oxygen (PaO₂) and other blood variables in 36 capybaras and the effect of different flows of nasal oxygen (O₂) supplementation. The capybaras were hand-injected with dexmedetomidine (5 μg/kg) and midazolam (0.1 mg/kg) and butorphanol (0.2 mg/kg) (DMB, n = 18) or methadone (0.1 mg/kg) (DMM, n = 18). One-third of the animals were maintained in ambient air throughout the procedure, and one-third were administered intranasal 2 L/min O₂ after 30 min whereas the other third were administered 5 L/min O₂. Arterial blood gases, acid-base status, and electrolytes were assessed 30 and 60 min after drug injection. The DMB and DMM groups did not vary based on any of the evaluated variables. All animals developed hypoxaemia (PaO₂ 44 [30; 73] mmHg, SaO₂ 81 [62; 93] %) 30 min before O₂ supplementation. Intranasal O₂ at 2 L/min improved PaO₂ (63 [49; 97] mmHg and SaO₂ [92 [85; 98] %), but 9 of 12 capybaras remained hypoxaemic. A higher O₂ flow of 5 L/min was efficient in treating hypoxaemia (PaO₂ 188 [146; 414] mmHg, SaO₂ 100 [99; 100] %) in all the 12 animals that received it. Both drug protocols induced hypoxaemia, which could be treated with intranasal oxygen supplementation.