Study of Rocuronium Onset Time According to Remifentanil Infusion

• the onset time of rocuronium [ Time Frame: 3 minutes [after injection of rocuronium when general anesthesia is induced.] ] [ Designated as safety issue: No ]
  Onset time of rocuronium was defined as the time from the end of its injection to the 95% depression of single twitch response, and it was measured by an anaesthesiologist, unaware of the group allocation.
  
  

• mean arterial pressure (MAP) [ Time Frame: 15 minutes [4 times; during the induction of general anesthesia as described below.] ] [ Designated as safety issue: No ]
  1. before induction (baseline): When a patient enter the operating room,
  2. at rocuronium administration: immediately before injecting rocuronium,
  3. before tracheal intubation: immediately before intubation,
  4. after tracheal intubation: immediately after intubation.
  
  
• heart rate (HR) [ Time Frame: 15 minutes [4 times; during the induction of general anesthesia as described below.] ] [ Designated as safety issue: No ]
  1. before induction (baseline): When a patient enter the operating room,
  2. at rocuronium administration: immediately before injecting rocuronium,
  3. before tracheal intubation: immediately before intubation,
  4. after tracheal intubation: immediately after intubation.
  
  
• cardiac output [ Time Frame: 15 minutes [4 times; during the induction of general anesthesia as described below.] ] [ Designated as safety issue: No ]
  1. before induction (baseline): When a patient enter the operating room,
  2. at rocuronium administration: immediately before injecting rocuronium,
  3. before tracheal intubation: immediately before intubation,
  4. after tracheal intubation: immediately after intubation.
  
  
• pain from the propofol infusion [ Time Frame: 1 minute [at the time when propofol is administered.] ] [ Designated as safety issue: No ]
  When propofol is administered for the induction of anesthesia, we investigate the pain by propofol.
  
  
• cough or chest wall rigidity from the remifentanil infusion [ Time Frame: 1 minute [at the time when remifentanil is infused.] ] [ Designated as safety issue: Yes ]
  when remifentanil is infused, the cough or chest wall rigidity is checked.
  
  

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.