Use of the laryngeal mask airway during magnetic resonance imaging

Laryngeal mask airway: a more successful method of insertion

STUDY OBJECTIVE

To compare the ease of insertion of the laryngeal mask airway (LMA) by two methods.

DESIGN

Prospective, randomized study.

SETTING

Operating room of a university-affiliated teaching hospital.

PATIENTS

350 ASA I, II, and III patients undergoing general anesthesia, in whom use of the LMA was not contraindicated.

INTERVENTIONS

With all routine monitors in place and after the induction of anesthesia with propofol, we compared the ease of insertion of the LMA in the two groups of 175 patients each. The timing of insertion was made on clinical grounds. In one group, the LMA was inserted with the cuff fully deflated, in the other group, the cuff was partially inflated (i.e., filled with half the recommended air in the cuff). When correct placement of the mask was not successful by one method, the other method was tried and the insertion graded in the same manner.

MEASUREMENTS AND MAIN RESULTS

The ease of insertion of the LMA was graded by the user on a scale of 1-4. Insertion of the LMA with the cuff partially inflated was significantly more successful (97.7%) than when the cuff was fully deflated (92%) (p < 0.05). When correct placement of the mask was not possible with the cuff fully deflated, partial inflation resulted in correct placement.

CONCLUSIONS

Inserting the LMA with the cuff partially inflated is likely to be more successful than with the cuff fully deflated. When it is not possible to insert the LMA with the cuff fully deflated, partial inflation before insertion may result in correct placement.

[Anesthesia for MRI examination]

Magnetic resonance imaging (MRI) requires the patients to stay for 30-45 min in a magnetic closed noisy space. Therefore most children and agitated adults require general anaesthesia or sedation in order to high quality images. Anaesthesia may be given by several routes (TIVA, inhalational or intrarectal administration) using common drugs. However, the magnetic field limits the selection of patients undergoing MRI and the spectrum of anaesthetic and monitoring equipment. The magnetic field may have deleterious effects on implanted ferromagnetic devices. It may attract objects towards the magnet centre at a dangerous speed. Moreover it may disturb the function of monitors and anaesthesia machines which should be tested for a specific magnetic field strength before introducing their use in a given MRI unit.