Experimental effects of chloral hydrate on ventilatory response to hypoxia and hypercarbia

The effect of chloral hydrate (CH)-induced sleep on inspiratory drive has not been systematically assessed. To determine the effects of CH on the ventilatory responses to hypercarbia and to hypoxia, nine unanesthetized adult rabbits with chronic tracheostomy were studied. We compared awake ventilatory measurements before CH to non-REM sleep assessments at 30, 60, 90, and 120 min after administration of 250 mg/kg of CH. There were no significant differences between any of these assessment intervals for respiratory rate, P_Aco₂, P_Ao₂, tidal volume (V_T), minute volume, T_i/T_tot, or V_T/T_i. Hypercarbic ventilatory response slopes were not diminished at any of the CH-sleep intervals compared to the awake mean slope. In addition, the ventilatory response to hypoxia at P_AO₂ = 70 mm Hg (V₇₀) and the hypoxic response slope demonstrated no significant decrease at any of the CH-sleep intervals. In summary, absence of any significant decrease in either hypercarbic or hypoxic ventilatory response after CH administration indicates absence of any CH effect on chemical inspiratory drive. Speculation: Sedation with chloral hydrate is an acceptable means of facilitating sleep for clinical assessments of chemical inspiratory drive. Chloral hydrate may also be the preferred drug whenever a sedative-hypnotic agent is necessary in patients with precarious pul-monary status or marginal central ventilatory drive.