Comparison of single-breath continuous positive airway pressure manoeuvre with inhaled salbutamol to improve oxygenation in horses anaesthetized for laparotomy.

Objective: To compare the efficacy of single-breath continuous positive airway pressure manoeuvre (CPAP-M) with inhaled salbutamol, and a combination of both.

Study Design: Randomized, clinical study.

Animals: A total of 62 client-owned horses (American Society of Anesthesiologists status III-V) anaesthetized for laparotomy.

Methods: Horses were premedicated with intravenous (IV) xylazine (0.4-0.6 mg kg), anaesthesia was induced with midazolam (0.06 mg kg IV) and ketamine (2.2 mg kg IV) and maintained with isoflurane in oxygen using volume-controlled ventilation without positive end-expiratory pressure. If PaO was < 100 mmHg (13.3 kPa), either a CPAP-M (50 cmHO for 45 seconds) or salbutamol (0.002 mg kg) was administered. The intervention was considered successful if PaO reached 100 mmHg (13.3 kPa). If PaO remained < 100 mmHg (13.3 kPa), treatments were switched. PaO/FiO ratio and estimated shunt fraction (F-shunt) were derived from data obtained from arterial blood gas measurements. Dynamic compliance (C) was calculated from variables recorded at the moment of arterial blood analysis. Fisher's exact tests compared success rates between treatments, and linear models were performed to test whether the treatment modified the values of the measurements; p < 0.05.

Results: Salbutamol was the first intervention in 28 horses and was effective in 22 horses. CPAP-M was the first intervention in 34 horses and was effective in 26 horses. CPAP-M after salbutamol was performed in six horses, with four responders, and salbutamol after CPAP-M was administered to eight horses, with one responder. Salbutamol, but not CPAP-M, significantly decreased F-shunt. Both salbutamol and CPAP-M significantly increased C.

Conclusions And Clinical Relevance: Salbutamol and CPAP-M were comparably effective in improving oxygenation and C in anaesthetized horses with PaO < 100 mmHg (13.3 kPa). Whether combining both treatments might be beneficial needs to be confirmed on a larger number of horses.