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The ProSeal laryngeal mask airway interferes with magnetic resonance imaging

Tarragona, Spain

To the Editor:

The laryngeal mask airway-ProSeal^TM (PLMA; The Laryngeal Mask Company, Henley on Thames, UK) is an evolution of the Classic laryngeal mask airway^TM (LMA-C; The Laryngeal Mask Company, Henley on Thames, UK) that presents two advantages. First the seal pressure is higher, 30 to 40 cm of water vs 20, and second, it allows drainage of stomach contents with an orogastric tube through the drain tube. All these characteristics and its usefulness in difficult airway management makes the PLMA an interesting device for airway management for anesthesia outside the operating room (radiology department, etc.).^1–3

However, the PLMA airway tube contains metal and could cause interferences during magnetic resonance imaging (MRI). We present the case of a four-year-old, 19 kg, with suspicion of a brain neoplasm, who needed general anesthesia for MRI. Sedation was contraindicated because of suspicion of a high intracranial pressure.

Before the procedure we conducted two trials with the PLMA; first we checked that the PLMA was not attracted by the MRI device (Magneton Harmony Maestro Class of 1 T, Siemens, UK); and second, we placed the PLMA at the right side of a phantom simulator and two MRI sequences (axial and sagittal) were obtained. (The phantom simulator is a bottle full of aqueous paramagnetic solutions like pure gels of gelatin, agar, polyvinyl alcohol, silicone, polyacrylamide, or agarose; organic dopped gells; paramagnetically dopped jells; and reverse micelle solutions. It is used by the radiologists to check the MRI machine). The PLMA was not attracted by the MRI but interfered with the MRI images (Figure).

View larger version (63K): [in this window] [in a new window]   FIGURE Axial and sagittal magnetic resonance imaging of phantom simulator with (left) and without (right) the ProSeal laryngeal mask airway.

We conclude that the PLMA interferes with head and neck MRI images but that it could be used for other imaging locations since it is not attracted by the magnetic field of the MRI machine.

References

1 Brain AI, Verghese C, Strube PJ. The LMA ‘ProSeal:’ –laryngeal mask with an oesophageal vent. Br J Anaesth 2000; 84: 650–4.[Abstract/Free Full Text]

2 Brimacombe J, Keller C. The ProSeal laryngeal mask airway. Anesthesiol Clin North America 2002; 20: 871–91.[Medline]

3 Farling PA. Anaesthesia in the magnetic resonance unit: a hazardous environment (Editorial). Anaesthesia 2002; 57: 421–3.[Medline]

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