Objective To compare arterial oxygen and carbon dioxide tensions in apneic and spontaneously ventilating horses recovering from anesthesia. Study design Randomized clinical trial. Animal population Forty-two healthy horses averaging 466±106kg and 6±5years of age. Methods Anesthetized horses undergoing a variety of surgical procedures and receiving positive pressure ventilation (IPPV) were divided into two equal groups. One group was allowed to return to spontaneous ventilation prior to disconnection from the anesthetic circuit (weaned). The other group remained apneic during transport to a recovery stall. Arterial blood gas data were collected at five time points: 20minutes before moving to a recovery stall (t=−20); at the time the anesthetic circuit was disconncted (t=0); at 3 and 5minutes post-disconnection (t=3 and t=5) and at the time of the first spontaneous breath (t=sv). The data were analyzed using an anova method for repeated measures and paired, two-tailed t-tests. Significance was assumed when p<0.05. Results The apneic group took a mean of 5minutes 18seconds (±135seconds) before starting spontaneous ventilation. This group maintained significantly higher PaO2 levels at intermediate time points (t=0 and t=3) but no difference was noted after 5minutes. PaCO2 levels were higher in the weaned group at time 0minutes, returning to a comparable level to the apneic group at t=3minutes. Conclusions and clinical relevance Horses can survive a short period of apnea during transport from the surgery suite to recovery stall and may benefit from a reduced incidence of transient hypoxemia compared with spontaneously ventilating horses. This information has practical implications for the anesthetist evaluating the options for discontinuing IPPV when horses are moved to a recovery stall.
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