Time course of ventilatory depression following induction doses of propofol and thiopental

To improve our understanding of the respiratory pharmacology of intravenous induction agents, the authors compared the acute effects of intravenous (iv) propofol 2.5 mg.kg-1 and iv thiopental 4.0 mg.kg-1 on the ventilatory response to CO2 (VeRCO2) of eight healthy volunteers. The slope of VeRCO2 decreased from 1.75 +/- 0.23 to a minimum of 0.77 +/- 0.14 1.min-1.mmHg-1 (mean +/- standard error) 90 s after propofol; similarly, the slope of VeRCO2 decreased from 1.79 +/- 0.22 to a minimum of 0.78 +/- 0.23 l.min-1.mmHg-1 30 s after thiopental. For both drugs, the slope was less than control in the 0.5-5-min period after injection (P less than 0.05). The slope returned to baseline within 6 min after thiopental; in contrast, after propofol, the slope remained less than control for the entire 20-min follow-up period (P less than 0.05 at 6-10, 11-15, and 16-20 min after injection). Also, from 6-10, 11-15, and 16-20 min after injection, the slope was less after propofol than at corresponding times after thiopental (P less than 0.05). Recovery of consciousness was approximately 4 min slower after propofol than after thiopental; nonetheless, awareness scores returned to baseline within 14 min after both drugs. The authors conclude that propofol 2.5 mg.kg-1 iv produces longer-lasting depression of VeRCO2 than a 4.0 mg.kg-1 iv dose of thiopental; after propofol, ventilatory depression may persist despite apparently complete recovery of consciousness.