Use of continuous positive airway pressure (CPAP) to optimise oxygenation in anaesthetised horses - a clinical study

Reasons for performing study: Hypoxaemia is a common problem during equine anaesthesia. Continuous positive airway pressure (CPAP) is a ventilation mode routinely employed in man to overcome hypoxaemia but has not been objectively assessed in horses. Objectives: To test the effects of CPAP on oxygenation and its indices in anaesthetised horses in a clinical setting. Methods: Twenty-four healthy horses requiring anaesthesia in dorsal recumbency were anaesthetised using a standard protocol. Following orotracheal intubation and connection to an anaesthetic machine capable of applying CPAP, horses were randomly allocated to ventilate at physiological airway pressure measured at the airway opening (Group PAP) or to receive CPAP of 8cmH₂O (Group CPAP). Arterial blood gas analysis was performed as soon as arterial cannulation was achieved and 30, 60 and 90min after induction. If PaCO₂ increased above 9.31kPa controlled ventilation was initiated. Groups were compared using a general linear model. Results: Horses receiving CPAP had significantly higher PaO₂ and calculated oxygen indices than horses receiving PAP. No significant differences in ventilation indices were observed between the 2 groups. Eight horses receiving PAP and 5 receiving CPAP required controlled ventilation. No differences in dobutamine requirements or mean arterial pressures were recorded. Conclusions: Continuous positive airway pressure of 8cmH₂O improved oxygenation indices in dorsally recumbent horses without significantly influencing ventilation. Potential relevance: Continuous positive airway pressure reduces the incidence of hypoxaemia in anaesthetised horses. Further research is warranted to elucidate the effects of CPAP on the cardiovascular system.