Ventilatory Responses to Hypoxia and Hypercapnia during Halothane Sedation and Anesthesia in Man

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Abstract
To elucidate the effects of halothane on chemical regulation of ventilation in man, the ventilatory responses to isocapnic hypoxia and hyperoxic hypercapnia was studied in 33 human subjects while fully conscious and during sedation or anesthesia with halothane, 0.1, 1.1, or 2 MAC [minimum anesthetic concentration]. In each group, the ventilatory effect of i.v. administration of doxapram, 0.4 mg/kg, was also measured. Halothane, 1.1 and 2 MAC, totally abolished the hypoxic response and nearly abolished the response to doxapram, while leaving the response to CO2 relatively brisk. Halothane, 0.1 MAC, decreased the responses to hypoxia and doxapram to less than a 3rd of control, but did not alter the response to CO2. Halothane selectively impaired 2 ventilatory responses mediated by peripheral chemoreceptors in man.