Hypoxic Ventilatory Drive in Dogs during Thiopental, Ketamine, or Pentobarbital Anesthesia

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Abstract
The ventilatory responses to isocapnic hypoxia and hypercapnia were studied in seven chronically tracheostomized dogs awake and during anesthesia with pentobarbital (30 mg/kg, iv), ketamine, or thiopental (10 and 15 mg/kg, respectively, followed by infusion). Isocapnic hypoxic ventilatory drive (HVD) was expressed as the parameter A such that the higher the A, the greater the hypoxic drive. HVD(A) was significantly reduced from 259 +/- 28 (mean +/- SEM) in awake dogs, to 96 +/- 14 after pentobarbital, 161 +/- 27 after thiopental, and 213 +/- 23 after ketamine. Hypercapnic ventilatory drive (HCVD) as measured by S (slope of the VE-PACO2 response curve) was significantly reduced from 1.3 +/- .32 in awake dogs to 0.4 +/- .13 after pentobarbital, 0.5 +/- .12 after thiopental, and 0.6 +/- .11 after ketamine. In addition, hypercapnia-induced augmentation of hypoxic drive was markedly diminished by the two barbiturates but was unaffected by ketamine. Therefore, ketamine at this dose level afforded greater protection during exposure to hypoxia than did barbiturates. (Key words: Ventilation, hypoxic response; Hypoxia, ventilation; Oxygen, ventilatory response; Carbon dioxide, ventilatory response; Anesthetics, intravenous, ketamine; Anesthetics, intravenous, thiopental; Hypnotics, barbiturates, pentobarbital.)

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