Effect of withholding feed on ventilation and the incidence of regurgitation during halothane anesthesia of adult cattle.

Six cows were anesthetized for 90 minutes with 1.5 minimal alveolar concentrations of halothane in oxygen, after 48 hours without food and 12 hours without water. On a separate occasion, the cows were allowed access to feed and water up to the time of induction of anesthesia, with the sequence of feeding vs fasting randomized. Every 15 minutes, measurements were made of end-tidal halothane concentration, arterial blood gas tensions, mean arterial blood pressure, heart and respiratory rates, tidal volume, minute volume, airflow rate, and transpulmonary pressure, and calculations were made of dynamic compliance and pulmonary resistance. Any regurgitation was recorded. Hypoventilation was noticed in all cows, but to a greater degree in fed cows. Fed cows became hypoxemic, whereas arterial oxygen tension did not change in nonfed cows. Alveolar-arterial oxygen tension gradient, tidal volume, and minute volume did not change. Arterial pH decreased progressively in all cows. Dynamic compliance also decreased progressively in all cows, and was consistently lower in fed cows. Pulmonary resistance tended to increase in all cows, but the increase was significant only in fed cows at 90 minutes. All fed cows became tympanitic, and 2 cows regurgitated a small volume of fluid at 55 minutes. Three nonfed cows regurgitated larger volumes at times ranging from 8 minutes to 85 minutes.