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