Background: Many studies have shown that tracheal intubation could be facilitated after induction with propofol and opioids without muscle relaxants. Remifentanil, which has a rapid onset and ultra-short duration of action, is a useful estrase-metabolized opioid (EMO) for tracheal intubation. This study was designed to evaluate the adequate induction dose of remifentanil with propofol 1.5 mg/kg for tracheal intubation without muscle relaxants.

METHODS: We have assessed intubating conditions in five groups of 57 female patients, ASA PS I or II. Each group was administerd intravenous propofol 1.5 mg/kg with remifentanil 1.0µ/kg, 2.0µ/kg, 3.0µ/kg, 4.0µ/kg and 5.0µ/kg, respectively. Intubation was attempted, and the intubating condition was scored by the degrees of relaxation of jaw (0-2), position of vocal cords (0-2) and the patient response (0-2). Mean arterial pressure (MAP) and heart rate (HR) were observed at each group.

RESULTS: The relationship between the concentration of remifentanil and the possibility of endotracheal intubation was as following: Probit (P) = - 1.38 (S.E.: 0.58) + 0.087 (S.E.: 0.23) × DRemi. The ED50 of remifentanil for endotracheal intubation without muscle relaxants was 2.12 (95% confidence interval: 1.42-2.62)µ/kg and the ED95 was 4.01 (95% confidence interval: 3.31-5.92)µ/kg.

CONCLUSIONS: We concluded that adequate dose of remifentanil which make possible to endotracheal intubation without muscle relaxants after induction of general anesthesia with 1.5 mg/kg of propofol is 4.01µ/kg in 95% of female patients and 2.12µ/kg in 50% of female patients.