Propofol Depresses the Hypoxic Ventilatory Response during Conscious Sedation and Isohypercapnia

Abstract

Propofol infusion at subanesthetic doses provides reliable conscious sedation. However, the ventilatory effects of sedative doses of propofol have not been established. The current study was conducted to determine the effects of propofol sedation on the hypoxic ventilatory response. Eight healthy, male volunteers received 1 mg.kg-1 propofol followed by a propofol infusion adjusted to maintain a constant, subanesthetic level of sedation. Hypoxic ventilatory response was measured using an isocapnic rebreathing technique: while keeping PETCO2 constant (approximately 6 mmHg above prestudy baseline), the authors continuously recorded minute ventilation and tidal volume, as oxygen saturation (SpO2) decreased from 98 to 70%. Hypoxic response determinations were performed before and during propofol infusion, as well as 30 and 60 min after termination of the propofol infusion. The slope of the hypoxic ventilatory response curve (VE vs. SpO2) decreased from 0.88 +/- 0.15 to 0.17 +/- 0.03 l.min-1.%SpO2 -1 during propofol sedation (mean +/- SE). Thirty minutes after discontinuation of the propofol infusion, slope returned to its prepropofol value. In addition, minute ventilation at SpO2 = 90% decreased during propofol sedation, from 16.1 +/- 0.8 to 8.7 +/- 0.4 l.min-1, accompanied by a similar decrease in tidal volume at SpO2 = 90%, from 1,099 +/- 87 to 523 +/- 21 ml. Thirty minutes after discontinuation of the propofol infusion, these variables also returned to their prepropofol values. The authors concluded that propofol infusion for conscious sedation significantly decreases the slope and causes a downward shift of the hypoxic ventilatory response curve measured during isohypercapnia.