title: Effect of halothane on hypoxic and hypercapnic ventilatory responses of goats.
abstract: We have measured the ventilatory responses to increased inspired carbon dioxide and to hypoxia in four goats awake and at 0.5%, 1.0% and 1.25% end-tidal halothane concentration. While maintaining PE'CO2 constant at each of three values (means 5.86, 6.45 and 7.2 kPa), PE'O2 was reduced rapidly from more than 25 kPa to 5.3-6 kPa for 3 min to record the increase in ventilation. Eleven sets of these 24 steady state points were obtained (2 PO2 x 3 PCO2 x 4 anaes. = 24). The mean isocapnic hypoxic ventilatory response (HVR) was 6.52 (SD 2.58) litre min-1 (n = 33) when awake, 5.62 (3.48) litre min-1 at 0.5% end-tidal halothane (ns), 3.05 (2.02) litre min-1 at 1% and 2.91 (2.12) litre min-1 at 1.25%, the last two being reduced significantly from awake and 0.5% halothane (P less than 0.05). With 1.25% halothane, HVR was reduced to 44.5 (18.6)% of the awake HVR. However, when HVR was expressed as % increase in ventilation produced by isocapnic hypoxia, it was 71 (19)% awake but 124 (65)% with 1.25% halothane, a significant increase with halothane (P less than 0.05). With 1.25% halothane, the carbon dioxide response slope decreased to 36.4 (26.4)% of control; hypoxia did not increase the slope significantly. Whereas previous studies in man have shown that halothane preferentially depresses hypoxic chemosensitivity and has a significant effect at 0.1 MAC, in the goat the hypoxic and carbon dioxide chemosensitivities were depressed equally. At 0.5% end-tidal concentration (about 0.5 MAC), halothane did not significantly depress hypoxic response.
authors.affiliation: Department of Anesthesia, University of California, San Francisco 94143-0542.
authors.forename: S O
authors.initials: SO
authors.lastname: Koh
authors.forename: J W
authors.initials: JW
authors.lastname: Severinghaus
mesh_terms: D000769:Anesthesia, Inhalation; D000818:Animals; D002245:Carbon Dioxide / Q000502:physiology*; D002628:Chemoreceptor Cells / Q000187:drug effects; D006041:Goats / Q000502:physiology*; D006221:Halothane; D008297:Male; D010100:Oxygen / Q000502:physiology*; D012119:Respiration
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen; D006221:Halothane