The halogenated volatile anesthetic agents decrease alveolar ventilation mainly through which of the following mechanisms?
A. Decrease in tidal volume
B. Decrease in respiratory rate
C. Decrease in ventilatory response to hypoxia
D. Decreased airway musculature tone
The answer is A. This a favorite question of Dr. Yaster. The halogenated agents (halothane, sevoflurane, isoflurane and desflurane) all depress the ventilatory drive and responsiveness to carbon dioxide in a dose dependent fashion. This is mainly done through a DECREASE IN TIDAL VOLUME. Respiratory rates tend to increase up to 1 MAC and then decrease at levels above 1 MAC. Decreased airway tone is an effect, but usually causes obstruction, not decreased alveolar ventilation.