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

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 (PaO(2)) and other blood variables in 36 capybaras and the effect of different flows of nasal oxygen (O(2)) 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 O(2) after 30 min whereas the other third were administered 5 L/min O(2). 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 (PaO(2) 44 [30; 73] mmHg, SaO(2) 81 [62; 93] %) 30 min before O(2) supplementation. Intranasal O(2) at 2 L/min improved PaO(2) (63 [49; 97] mmHg and SaO(2) [92 [85; 98] %), but 9 of 12 capybaras remained hypoxaemic. A higher O(2) flow of 5 L/min was efficient in treating hypoxaemia (PaO(2) 188 [146; 414] mmHg, SaO(2) 100 [99; 100] %) in all the 12 animals that received it. Both drug protocols induced hypoxaemia, which could be treated with intranasal oxygen supplementation.