Bite block or not?
A case study by Usamah Kidwai and colleagues on their experience of using reinforced laryngeal mask airways
The laryngeal mask airway (LMA) revolutionised anaesthetic practice when it was introduced. Since then, there have been many different variations on the basic form introduced.
The use of standard or reinforced LMA is a common practice in elective or emergency situations because it avoids kinking and is easy to position and provides secure airway for spontaneous breathing or assisted ventilation, without requiring endotracheal intubation .
In comparison with standard LMA, reinforced LMA is longer with a smaller diameter and is flexible and wire-reinforced. It has been widely used in elective ophthalmic procedures. The rise in intraocular pressure is lower with LMA insertion than with endotracheal intubation and during emergence from anaesthesia.
We would like to share our experience of using reinforced LMA in a middle-aged gentleman with severe learning difficulties, who came in for an elective ophthalmic procedure.
On airway examination, he was Mallampati grade II, with a full set of his own teeth. The plan was to use reinforced LMA, as tracheal intubation was not necessary because the patient was fasting and there was no history of reflux.
Induction of general anaesthesia was uneventful using fentanyl 100 mcg and propofol 200mg. A Size 4 reinforced LMA was checked for integrity and inserted. Anaesthesia was maintained with sevoflorane and 50 per cent oxygen and air. The procedure was uneventful and the patient was transferred to the recovery area, spontaneously breathing with the reinforced LMA in situ.
On emergence, the patient started biting on the LMA. His airway remained patent with SpO2 of 96–98 per cent. He remained vitally stable during this time with no signs of airway obstruction.
After a lot of convincing, the patient opened his mouth and the LMA was taken out. The LMA shaft was found to be severed and its cuff was attached to the shaft with a single wire (see image).
This event reminds us of the recommended use of a bite block alongside the LMA . A bite block can be made with a sterile gauze roll taped in to a cylindrical shape placed alongside the LMA. Alternatively, a Guedel airway may be used . Bite blocks are not routinely used in our department and this so far has not led to any adverse incidents.
The benefits of removal of LMA in patients under light plane of anaesthesia may not outweigh the potential risks, especially if the patient is transferred to the recovery ward with an LMA in situ .
We can debate that it may be safer to remove the LMA while the patients are in a deeper plane of anaesthesia .
Two studies have demonstrated a very high incidence of clenched teeth and biting the LMA – 26 per cent and 10 per cent respectively – when the airway is removed after laryngeal reflexes have returned [5,6].
Although the use of LMA is associated with minimal or rare complications, each airway should be carefully inspected before its use. The learning points from this episode are that, unless a device which intrinsically resists biting force, such as an IGel is to be used, a bite block of some description should be utilised with an LMA type device as recommended.
Usamah Kidwai (SCF Anaesthetics), P. Sri-Ganeshan (consultant anaesthetist), P. Surve (SD anaesthetist), V. Dalal (AS anaesthetist) and R. Cozma (SD anaesthetist), are all based at the Princess Royal University Hospital, Farnborough, Kent.
Fred J. Spielman, Complete separation of tube from the mask during removal of a disposable LMA – Canadian J. Anaesthesia. Nov 2002. Vol 49 Issue 9 pg. 990-992
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