The investigators therefore hypothesized that remifentanil could prolong the onset time of rocuronium, and evaluated the effect of remifentanil on the hemodynamic profiles (arterial pressure and heart rate) during the anesthetic induction sequence.

It has been reported that co-administration of ephedrine reduced the onset time of neuromuscular block of rocuronium (1-3). It also provided an improved condition for the rapid tracheal intubation (2,4). This beneficial effect was attributed to the increased cardiac output and tissue perfusion to muscle, and therefore, a more rapid delivery of rocuronium to the neuromuscular junction was achieved (4-5). If so, any drugs which decrease cardiac output consequently can prolong the onset time of rocuronium.

Remifentanil is the first ultra-short acting opioid with a rapid onset. During the total intravenous anesthesia (TIVA) with propofol and remifentanil, prior administration of remifentanil could reduce the propofol infusion pain without other significant complications (6). However, remifentanil can decrease the arterial pressure and heart rate (7-8), so that it is likely to decrease the onset time of rocuronium for the opposite principle that ephedrine increases it.

The investigators therefore hypothesized that remifentanil could prolong the onset time of rocuronium, and evaluated the effect of remifentanil on the hemodynamic profiles (arterial pressure and heart rate) during the anesthetic induction sequence.

Inclusion criteria:

• American Society of Anesthesiologist physical status I or II
• Aged 20-65 yr
• Elective surgery under general anesthesia with total intravenous anesthesia
• 8.5 kg/m2 < body mass index (BMI) < 25 kg/m2

Exclusion criteria:

• BMI > 25 kg/m2 or < 18.5 kg/m2
• Any cardiovascular or neuromuscular disease
• Intake of drugs known to interact with the neuromuscular junction
• Patients wit risk of pulmonary aspiration
• Anticipated difficult airway
• history of known allergy to rocuronium