Arterial oxygen and carbon dioxide tensions in conscious laterally recumbent ponies

Six adult ponies were trained calmly to assume and maintain left lateral recumbency without the use of sedative or immobilising agents. During a 30 min recumbent period, pHa, arterial oxygen and carbon dioxide tensions (PaO2 and PaCO2) and heart and respiratory rates were monitored at regular intervals to evaluate ventilatory response. Overall, there were no statistically significant differences found between mean control and recumbent or final standing values. When lightweight ponies were compared to heavyweight ponies, only mean PaO2 at 10 mins recumbency was different. This information supports the hypothesis that ventilation impairment during the first 30 mins of equine general anesthesia is primarily drug-mediated, rather than initiated by recumbency per se.