Cardiopulmonary effects of oral trazodone administration prior to isoflurane anesthesia in healthy horses.

Objective: To determine the cardiopulmonary effects of oral trazodone before isoflurane anesthesia in systemically healthy horses.

Methods: 12 horses donated for euthanasia (from August 2022 through June 2023) due to conditions unrelated to the cardiovascular system were included in this prospective, randomized, controlled trial. Horses were assigned to receive oral trazodone (6 mg/kg; n = 7) or corn syrup (n = 5) 1 hour before xylazine (1 mg/kg, IV) sedation, ketamine (2.2 mg/kg, IV) and propofol (0.7 mg/kg, IV) induction, and anesthetic maintenance with inhaled isoflurane (target 1.6% expired) for 75 minutes. Dobutamine (1 μg/kg/min, IV) was administered during the last 15 minutes of anesthesia before euthanasia. The primary outcome cardiac index (CI; saline thermodilution technique) was recorded at baseline, 1 hour after oral dosing, after sedation and induction, and every 15 minutes under anesthesia. Data were compared between groups using a mixed model.

Results: All 12 horses completed the study. No significant differences were observed between groups at all time points except after dobutamine infusion, where CI (mean ± SD) was significantly higher in the trazodone group (66.2 ± 16.8 mL/min/kg) than the control group (46.8 ± 6.6 mL/min/kg). One horse in the trazodone group displayed signs of colic after dosing, with markedly reduced CI during anesthesia compared to all other horses.

Conclusions: Oral trazodone before isoflurane anesthesia in healthy horses produced variable cardiovascular function, including profound cardiovascular depression in 1 horse.

Clinical relevance: Profound individual cardiovascular responses may be seen with routine preanesthetic trazodone in horses.