• Martina Mosing, Paul MacFarlane, David Bardell, Laura Lüthi, Peter J Cripps, and Regula Bettschart-Wolfensberger.
• Division of Anaesthesiology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland. mmosing@vetclinics.uzh.ch.
• Vet Anaesth Analg. 2016 Nov 1; 43 (6): 611-622.

ObjectiveTo evaluate the effects of continuous positive airway pressure (CPAP) on intrapulmonary shunt, cardiac output and oxygen delivery in horses subjected to a 6 hour period of general anaesthesia.Study DesignRandomized, experimental, crossover study.AnimalsTen healthy adult horses.MethodsFollowing medetomidine, diazepam and ketamine administration, orotracheal intubation was performed and horses positioned in dorsal recumbency. Anaesthesia was maintained with isoflurane carried in an oxygen and air mix (FiO2 0.5) combined with a medetomidine infusion. Horses were anaesthetized twice and either CPAP (8 cmH2 O) or physiologic airway pressure (NO CPAP) was applied to the lungs for 6 hours; the order of treatments was randomly assigned. Following induction of anaesthesia, cardiovascular and respiratory variables (including arterial blood gas analysis) were recorded every 30 minutes, cardiac output was measured every 60 minutes using the lithium dilution technique and oxygen delivery calculated. If PaCO2 exceeded 100 mmHg (13.3 kPa), controlled ventilation was initiated and horses excluded from further data collection. Groups were compared using a general linear model.ResultsData from eight horses were analysed. PaO2 was 15-56 mmHg (2.00-7.45 kPa) higher (p < 0.001) and shunt fraction 6-14% lower (p < 0.001) in the CPAP group. No differences were seen for cardiac output and oxygen delivery. The lack of difference in oxygen delivery was attributed to lower haemoglobin levels in the CPAP group than in the NO CPAP group.Conclusions And Clinical RelevanceCPAP of 8 cmH2 O can be used in dorsally recumbent horses to decrease pulmonary shunt fraction without causing a decrease in cardiac output during longterm anaesthesia.© 2016 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesia and Analgesia.

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