Comparison of inhaled salbutamol and salmeterol for the treatment of arterial hypoxaemia in anaesthetized horses: a randomized clinical trial.

Objective: To compare the efficacy of inhaled salbutamol with salmeterol for the treatment of arterial hypoxaemia in anaesthetized horses.

Study Design: Prospective, randomized, clinical study.

Animals: A total of 108 client-owned horses (American Society of Anesthesiologists status I-V) anaesthetized for elective and emergency procedures.

Methods: Horses were premedicated with acepromazine [intramuscularly 0.1 mg kg or intravenously (IV) 0.05 mg kg] and xylazine (0.6 mg kg IV). Midazolam (0.06 mg kg IV) and ketamine (2.2 mg kg IV) were combined to induce anaesthesia, and isoflurane in oxygen/air mixture (inspired oxygen fraction 0.7) was used for maintenance of anaesthesia. Mechanical ventilation was initiated without delay using the following ventilator settings: tidal volume 10 mL kg, respiratory rate 8 breaths minute, inspiratory-to-expiratory time ratio 1:2, no positive end-expiratory pressure. If arterial blood gas analysis revealed PaO < 100 mmHg (13.3 kPa), the administration of either inhaled salbutamol (2 μg kg) or salmeterol (0.5 μg kg) was randomly assigned Blood gas analysis was repeated 15 and 30 minutes after treatment. The intervention was considered successful when PaO after treatment ≥ 1.2 × PaO before treatment (i.e. ≥20% increase). PaO at 15 and 30 minutes was compared between groups using Mann-Whitney U test; p < 0.05 was considered significant.

Results: Of the 108 horses, 60 were administered salbutamol, 65% and 60% responded successfully at 15 and 30 minutes, increasing their initial PaO by 38% and 44%, respectively. The other 48 horses were administered salmeterol, 35% responded successfully at 15 and 30 minutes, increasing their initial PaO by 3% and 4%, respectively. PaO was significantly higher after salbutamol than after salmeterol at 15 and 30 minutes.

Conclusions And Clinical Relevance: Using the described protocol, inhaled salbutamol was more effective than salmeterol in improving PaO in anaesthetized horses with value < 100 mmHg (13.3 kPa).