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This study evaluated the breathing pattern and distribution of ventilation in horses prior to and following recovery from general anaesthesia using electrical impedance tomography (EIT). Six horses were anaesthetised for 6 hours in dorsal recumbency. Arterial blood gas and EIT measurements were performed 24 hours before (baseline) and 1, 2, 3, 4, 5 and 6 hours after horses stood following anaesthesia. At each time point 4 representative spontaneous breaths were analysed. The percentage of the total breath length during which impedance remained greater than 50% of the maximum inspiratory impedance change (breath holding), the fraction of total tidal ventilation within each of four stacked regions of interest (ROI) (distribution of ventilation) and the filling time and inflation period of seven ROI evenly distributed over the dorso-ventral height of the lungs were calculated. Mixed effects multi-linear regression and linear regression were used and significance was set at p<0.05. All horses demonstrated inspiratory breath holding until 5 hours after standing. No change from baseline was seen for the distribution of ventilation during inspiration. Filling time and inflation period were more rapid and shorter in ventral and slower and longer in most dorsal ROI compared to baseline, respectively. In a mixed effects multi-linear regression, breath holding was significantly correlated with PaCO2 in both the univariate and multivariate regression. Following recovery from anaesthesia, horses showed inspiratory breath holding during which gas redistributed from ventral into dorsal regions of the lungs. This suggests auto-recruitment of lung tissue which would have been dependent and likely atelectic during anaesthesia.

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In dorsally recumbent anaesthetized horses, CPAP of 8 cmHO results in redistribution of ventilation towards the dependent lung regions, thereby improving ventilation-perfusion matching. This improvement was not associated with an increase in dead space indicative for a lack in distension of the airways or impairment of alveolar perfusion.

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There is an increasing awareness of the development of hyperkalaemia during anaesthesia in otherwise healthy veterinary patients. In the human literature 63 per cent of in-hospital hyperkalaemic episodes are associated with drug administration. Anecdotal veterinary reports have suggested that a genetic component may also play a role, with greyhounds seemingly more susceptible to the development of hyperkalaemia under anaesthesia. This case report identifies the repeated development of hyperkalaemia, and its treatment, during two separate episodes of general anaesthesia in a nine-year-old, female neutered greyhound. The first episode of hyperkalaemia (7.89 mmol/l) was identified due to bradycardia and second-degree atrioventricular block on electrocardiogram. Treatment was with intravenous calcium gluconate, insulin, glucose and fluid therapy. The second episode (6.60 mmol/l) was associated with spiked T-waves, and treatment was with insulin and glucose infusions to allow completion of the anaesthetic and surgery. Possible causes and treatments are discussed, and the need for reporting of such cases is highlighted.

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.