Hemoglobin desaturation after propofol/remifentanil-induced apnea: a study of the recovery of spontaneous ventilation in healthy volunteers.

Background: In an earlier study investigating the "can't ventilate/can't intubate" clinical scenario, induction of anesthesia with thiopental 5 mg/kg and succinylcholine 1.0 mg/kg was associated with a significant risk of hemoglobin desaturation. It appeared that succinylcholine-induced apnea was responsible for the prolonged apnea. Our hypothesis was that using propofol and remifentanil for tracheal intubation might avoid prolonged apnea and subsequent desaturation attributable to muscle relaxation.

Methods: Twenty-four healthy volunteers ages 18 to 45 years participated. After oxygen administration to end-tidal oxygen >90%, volunteers received 2 mg/kg propofol and remifentanil either 2 mcg/kg (group 1; n = 12) or 1.5 mcg/kg (group 2; n = 12). Oxygen saturation (SpO(2)) was measured at a finger, an ear lobe, and the forehead. If SpO(2) decreased below 80%, volunteers received chin lift and, if persistent, assisted ventilation.

Results: Desaturation (SpO(2) < 80%) occurred in 5 volunteers: 4 in the higher remifentanil dose (2 mcg/kg) group and 1 in the lower dose (1.5 mcg/kg) group. Chin lift and assisted ventilation was necessary in 3 volunteers. The lowest SpO(2) was 82.4 ± 10.5 (mean ± SD) in the higher-dose group vs. 92.4 ± 8.6 with the lower dose of remifentanil (P = 0.019). Apnea time was shorter (P = 0.0093) with the lower dose (4.7 ± 1.5) than with the higher dose of remifentanil (6.1 ± 1.0). Conditions for intubation were excellent or acceptable in 11 volunteers (92%; 95% confidence interval [CI], 65%-99%) in the higher-dose group, and in 8 (67%; 95% CI, 39%-86%) with the lower dose.

Conclusions: Administered with propofol 2 mg/kg, the remifentanil dose necessary to produce acceptable intubating conditions, 2 mcg/kg, produces apnea that carries a significant risk of desaturation, whereas a remifentanil dose of 1.5 mcg/kg does not reliably produce acceptable intubating conditions and does not eliminate the risk of desaturation.