Dose-dependent effects of halothane on the phrenic nerve responses to acute hypoxia in vagotomized dogs
Abstract
Previous studies in dogs and humans suggest that the carotid body chemoreceptor response to hypoxia is selectively impaired by halothane. The present studies in an open-loop canine preparation were performed to better delineate the effects of anesthetic concentrations of halothane on the carotid body chemoreceptor-mediated phrenic nerve response to an acute hypoxic stimulus. Three protocols were performed to study the effects of halothane anesthesia on the phrenic nerve response to 1 min of isocapnic hypoxia (partial pressure of oxygen [PaO2] at peak hypoxia, 35-38 mmHg) in unpremedicated, anesthetized, paralyzed, vagotomized dogs during constant mechanical ventilation. In protocol 1, the dose-dependent effects of halothane from 0.5-2.0 minimum alveolar concentration (MAC) on the hypoxic response during moderate hypercapnia (partial pressure of carbon dioxide [PaCO2], 60-65 mmHg) were studied in 10 animals. In protocol 2, the hypoxic responses at 1 MAC halothane near normocapnia (PaCO2, 40-45 mmHg) and during moderate hypercapnia were compared in an additional four animals. In protocol 3, the hypoxic response of 4 of 10 dogs from protocol 1 was also studied under sodium thiopental (STP) anesthesia after they completed protocol ...Continue Reading
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