March 1998

Tracheal intubation in ambulatory patients: Using remifentanil and propofol without muscle relaxants.
Stevens JB, Wheatley L. Anesth Analg 1998;86:45-9.
[ see abstract below ]

Tracheal intubation is usually facilitated by administering a muscle relaxant. However, for ambulatory surgery patients, it is important to avoid the side effects of our anesthetic interventions. Specifically, the use of succinylcholine as muscle relaxant is associated postanesthetic myalgias, as well as less common but more serious complications.

The use of nondepolarizing muscle relaxants usually requires antagonism and risks the complications of those drugs, including residual block and increased postoperative nausea and vomiting. Therefore, clinicians have sought to develop techniques to perform tracheal intubation which do not include the use of muscle relaxants. Tracheal intubation has been performed without a muscular block in patients who have received alfentanil followed by propofol, but the large doses of alfentanil (40 µg/kg) have a clinical duration which is inappropriate for many ambulatory surgery procedures. Remifentanil has onset characteristics similar to alfentanil but has a shorter duration of action. Therefore, these authors studied the use of propofol with remifentanil as the opioid in this intubation technique.

The authors studied 80 patients scheduled to undergo elective ambulatory surgery with normal appearing airway anatomy. Patients with coronary artery, airway disease or greater than 30% obesity were excluded. After midazolam premedication, patients were randomized to receive either 1, 2, 3, or 4 µg/kg remifentanil. The opioid was given as a 90 second infusion, and 60 seconds after beginning the remifentanil infusion, propofol 2 mg/kg was administered using handheld syringe. Patients were ventilated by mask when unconscious. Ninety seconds after propofol administration, intubation was attempted using a Macintosh 3 laryngoscope blade and a 7- or 8-mm endotracheal tube, by gender.

The intubating anesthesiologist assessed mask ventilation, jaw relaxation, vocal chord position and patient response to intubation, to create an overall intubating score of excellent, good, or poor. Time from the onset of apnea until the return of spontaneous ventilation was recorded in all patients at 1 minute intervals. Maintenance of anesthesia was with sevoflurane and nitrous oxide.

Mean blood pressure values decreased significantly after induction of anesthesia in all groups and remained significantly lower than baseline in the 2-4 µg/kg groups. Heart rate decreased significantly from pre-induction level in the 3 and 4 µg/kg groups, and remained lower than baseline at all times. No patient demonstrated clinically significant rigidity during the period of mask ventilation, and the jaw was relaxed in all patients. Vocal chords were significantly less likely to be closed in patients receiving 1 µg/kg. However, patients in this group were also more likely to have an unacceptable response to laryngoscopy and intubation. Overall intubating conditions were significantly better in the 3 and 4 µg/kg group. The duration of apnea was less than 5 minutes in all groups.

The results of this study suggest that propofol 2 mg/kg administered with the remifentanil 3-4 µg/kg reliably provides good or excellent conditions for tracheal intubation in healthy patients with favorably airway anatomy. The lowest adequately effective dose was 3 µg/kg. However, there are several precautions which the clinician should observe. Remifentanil 1-3 µg/kg over 60 sec with similar doses of propofol, 0.5-2 mg/kg have been associated with clinically significant muscle rigidity in other studies.

The authors of this study did not see rigidity, which may be related to their use of both a full dose of propofol 2 mg/kg and a slower administration of remifentanil, over 90 seconds. The clinician should also be aware of the vital signs changes which may occur. Induction of anesthesia with propofol and remifentanil in these doses resulted in significant decrease in blood pressure and heart rate values. Such decreases are well tolerated in the healthy well hydrated outpatient. However, caution should be observed for hypovolemic or debilitated patients who will not tolerate these changes. Another opioid side effect, postoperative nausea and vomiting, was not assessed in this study, but the possibility of PONV after this higher-dose opioid technique should be considered and monitored.

In conclusion the authors describe a technique that will permit tracheal intubation without muscle relaxants in ambulatory patients, consisting of propofol 2 mg/kg and remifentanil 3 µg/kg. As with all techniques it has associated side effects, and the use of this approach should be considered for patients where the disadvantages of muscle relaxants are greater than the disadvantages of this technique.

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ABSTRACT