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LETTERS TO THE EDITOR

Laryngeal Mask Usage in the Unstable Neck

Departments of Anaesthesia and Intensive Care University of Queensland Cairns Base Hospital Cairns, Australia

C. Keller, MD

Departments of Anaesthesia and Intensive Care University of Innsbruck Innsbruck, Austria

We read with interest the article by Asai and Shingu (1) describing exchange of a tracheal tube (TT) for a laryngeal mask airway (LMA) to prevent dislodgement of an implanted bone during emergence from cervical spine surgery. In view of the favorable emergence characteristics of the LMA compared with the TT (2) and the high success rates for insertion despite manual-in-line traction (3), using the LMA in this situation would seem appropriate. However, the standard insertion technique involves pressing the LMA firmly into the posterior palatopharyngeal curve using the index finger, and we hypothesized that high pressures could be exerted against the cervical vertebrae during LMA insertion, with possible implications for the unstable cervical spine. To test this hypothesis, we surgically implanted small pressure sensors (accurate to 1%) into the pharyngeal surface of the second and third cervical vertebrae of 20 fresh adult cadavers and measured the pressure during insertion with the standard technique. We found that the pressure was 224 (95% CI 161–286) cm H₂O, decreasing rapidly to <20 cm H₂O once insertion was complete. We are uncertain as to the clinical importance of this finding, but given the acceptance of the LMA for use in the unstable cervical spine (4,5), we consider that research is urgently needed to determine the implications (if any) of this finding. Meanwhile, we recommend that clinicians be careful to avoid excessive posterior force when using the LMA in the unstable cervical spine. Perhaps consideration should also be given to using an alternative insertion technique, such as the Guedel technique (6), that does not involve pressing the index finger into the posterior pharyngeal wall. We would not recommend using the intubating LMA as an alternative (although it does not require use of the index finger for insertion) because it has recently been shown to exert substantial static pressures (approximately 160 cm H₂O) against the mucosa overlying the cervical vertebrae, and the implications of this have not been evaluated (7).

References

1. Asai T, Shingu K. Use of the laryngeal mask during emergence from anesthesia in a patient with an unstable neck. Anesth Analg 1999;88:469–470.[Free Full Text]
2. Brimacombe J. The advantages of the LMA over the tracheal tube or facemask: a meta-analysis. Can J Anaesth 1995;42:1017–23.[Web of Science][Medline]
3. Brimacombe J, Berry A. Laryngeal mask airway insertion: a comparison of the standard versus neutral position in normal patients with a view to its use in cervical spine instability. Anaesthesia 1993;48:670–1.[Web of Science][Medline]
4. Dhillon AR. Use of laryngeal mask airway in cervical manipulation [letter]. Anaesthesia 1996;51:408.[Web of Science][Medline]
5. Harding D, Bihari D. Airway control in a patient with an unstable cervical fracture and delirium tremens [letter]. Br J Hosp Med 1995;54:59.[Web of Science][Medline]
6. Brimacombe J, Berry A. Insertion of the laryngeal mask airway: a prospective study of four techniques. Anaesth Intensive Care 1993;21:89–92.[Web of Science][Medline]
7. Brimacombe J, Keller C. Cervical spine instability and the intubating laryngeal mask: a caution [letter]. Intensive Care 1999;26:708.

Response

Department of Anesthesiology Kansai Medical University Moriguchi City, Osaka, Japan

We thank Brimacombe et al. for their helpful comment on our article (1). As they suggest, the advantages of using the laryngeal mask in the patient with an unstable neck should be weighed against the disadvantages, such as the theoretical risk of excessive pressure exerted by the mask on the fragile cervical spine.

They state that they would not recommend using the intubating laryngeal mask in the patient with an unstable neck (although the pressure exerted by the intubating mask they report seems not much different from the pressure exerted by the conventional laryngeal mask). We have found that placement of the intubating laryngeal mask is significantly easier and faster than the conventional mask while the patient’s head and neck are stabilized by the manual in-line method (2). Therefore, the role of the intubating laryngeal mask in this group of patients should also be established based on its advantages and disadvantages.

References

1. Asai T, Shingu K. Use of the laryngeal mask during emergence from anesthesia in a patient with an unstable neck. Anesth Analg 1999;88:469–70.
2. Asai T, Wagle AU, Stacey M. Placement of the intubating laryngeal mask is easier and faster than the laryngeal mask during manual in-line neck stabilization. Br J Anaesth. In press.

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