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Correspondence |
University of Western Ontario, London, Canada, E-mail: tturkstr{at}uwo.ca
To the Editor:
Airway management can present challenges during conscious sedation for specialized cases performed under regional or local anesthesia such as awake craniotomy.1,2 When progressive sedation levels are required, initially the airway can be managed with the laryngeal mask airway (LMA; LMA North America, San Diego, CA, USA) or the single-use LMA-Unique (LMA-U).3 If airway protection is needed or positive pressure ventilation is required, conversion to an endotracheal tube (ETT) may then be warranted. Blind passage of a standard ETT through the LMAU is rarely successful, with less than 25% success in one series4 but fibreoptic guidance may provide visualization for intubation.5 We have modified an LMA-U and ETT to successfully secure the airway.
A middle-aged patient underwent awake craniotomy in right lateral decubitus position with his head fixed in Mayfield pins. After cerebral mapping was completed the patient was re-sedated, but he then became increasingly restless; it was impossible to find a balance of immobility and comfort without airway obstruction and apneic events. A size 4 LMA-U was inserted, allowing the patient to breath spontaneously. After three hours, gastric contents appeared in the anesthesia circuit, mandating endotracheal intubation to protect the airway. The fibreoptic bronchoscope (FOB) was advanced easily into the trachea with the LMA-U in place. However, a bed-side trial of similar components revealed that a suitably sized ETT could not be advanced through the LMA-U. A larger #5 LMA was not helpful because the limiting factor was the circuit connector. The intubating LMA could not be inserted properly due to the patient’s position. A solution was found to achieve fibreoptic assisted endotracheal intubation via the LMA-U. This was based on the following components: a modified LMA-U, armoured ETT, and a cut ETT to be used as a "pusher", if removal of the LMA-U was necessary.
The circuit connector plus 2–4 cm of the tube can be cut from the LMA-U and replaced with a lubricated connector from a standard size 8.5 ETT. The LMA-U with removable connector can be inserted in the usual fashion and used to ventilate the patient. If endotracheal intubation is required, the LMA-U circuit connector is removed and an armoured ETT can be advanced over a FOB into the trachea under direct guidance. The ETT can then be used to ventilate the patient with the LMA-U in situ (cuff deflated). The armoured ETT is preferable because it has a more proximal exit point for the pilot balloon, facilitating LMA-U removal, and because it has a smaller balloon, which deflates without kinking to allow easier passage through the LMA-U. The Table
shows the applicable sizing for the required components.
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In situations where the intubating LMA cannot be used because of patient or positioning factors, application of the LMA-U with this modification may become especially useful to facilitate endotracheal intubation with fibreoptic guidance. This technique could also be potentially useful in a situation where intubation is desired and the LMA-U is already in situ. The ETT connector could be cut from the LMA-U and replaced with the detachable connector, although it goes against conventional wisdom to sever the connector from an in-situ airway device. A limitation of this technique is that currently available sizes (3, 4, and 5) of the LMA-U limit maximal ETT sizes to 6.0, 6.5, and 7.0, respectively.
With this modification, the disposable LMA-Unique can be used to assist with tracheal intubation when transitioning from conscious sedation to general anesthesia, or in a situation where intubation through an LMA is the preferred option to secure the airway. With increased use of the disposable LMA-U, this technique may become a valuable tool in the anesthesiologist’s airway armamentarium.
Footnotes
Accepted for publication September 7, 2006.
References
1 Sarang A, Dinsmore J. Anaesthesia for awake craniotomy - evolution of a technique that facilitates awake neurological testing. Br J Anaesth 2003; 90: 161–5.
2 Costello TG, Cormack JR. Anaesthesia for awake craniotomy: a modern approach. J Clin Neurosci 2004; 11: 16–9.[Medline]
3 Cook TM. The classic laryngeal mask airway: a tried and tested airway. What now? (Editorial). Br J Anaesth 2006; 96: 149–52.[Medline]
4 Barnes DR, Reed DB, Weinstein G, Brown LH. Blind tracheal intubation by paramedics through the LMAUnique. Prehosp Emerg Care 2003; 7: 470–3.[Medline]
5 Osborn IP, Soper R. It’s a disposable LMA. Just cut it shorter – for fiberoptic intubation. Anesth Analg 2003; 97: 299–300.
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