Myasthenia gravis (MG), a disorder of the neuromuscular junction, is associated with unusual sensitivity to muscle relaxants. The use of muscle relaxants in MG patients may increase the risk of unsuccessful extubation and postoperative respiratory failure, so the use of an anesthetic technique with avoidance of muscle relaxants has been recommended.1,2 Past reports indicate that remifentanil and propofol administered without muscle relaxants is a suitable regimen of anesthesia in MG patients.3−6 Remifentanil 3−4 μg/kg, in combination with propofol 2.0 mg/kg, reliably provides good to excellent conditions for tracheal intubation without a muscle relaxant in elective surgery for myasthenic patients.1,2,5,6 In these reports, laryngoscopy was performed some 60−90 seconds after remifentanil-propofol sequential administration, indicating that the response induced by the laryngoscope is suppressed within 60−90 seconds after administration. Thus, it should be possible to intubate the trachea within this period.
A new intubation device, the Pentax-AirWay Scope® (AWS; Pentax, Tokyo, Japan) has been reported to facilitate more rapid, more reliable, and less stressful tracheal intubation than a conventional laryngoscope.2 We therefore hypothesized that the use of AWS in MG patients in remifentanil-propofol rapid sequence intubation might reduce the stress of intubation, which in turn would decrease the required dose of remifentanil and lessen the risk of inducing cardiac depression.
Five female MG patients (American Society of Anesthesiologists class I−III) were scheduled for thymectomy. Following preoxygenation with 100% oxygen for 2 minutes, the patients received rapid intravenous administration of 2.0 μg/kg remifentanil, followed immediately by rapid intravenous administration of 2.0 mg/kg propofol. Sixty seconds after the remifentanilpropofol sequence, tracheal intubation was performed using the AWS.
In all cases, intubation was successfully performed under excellent conditions. In all patients, the vocal cords were completely open, the jaw was relaxed, and there was no coughing or movement after tube placement. Blood pressure and heart rate transiently decreased, but within clinically acceptable limits.
Anesthesia was maintained with remifentanil 0.1−0.3 μg/kg/min and 1% sevoflurane in air/oxygen. After recovery of adequate tidal volume and consciousness, the tracheal tube was removed. The postoperative course was uneventful and respiratory support was not required.
Our report verifies that a lower dose of remifentanil (2.0 μg/kg) than that indicated in previous reports can also provide good conditions for tracheal intubation without the use of muscle relaxants in MG patients. The use of AWS in combination with remifentanil-propofol sequence induction provides an excellent option for a rapid sequence intubation in myasthenic patients.