Fibre optic intubation via a conduit is a relatively low skill technique that can be very useful in the management of the difficult airway, both anticipated and unanticipated. In the case of the unanticipated difficult airway, it might form part of Plan B of the DAS guidelines (the “can’t intubate can ventilate” situation). The technique can also be used electively in the management of the known difficult airway and in patients with C-spine injuries.
The conduits used for this technique include laryngeal mask airways (LMAs), of which there are many types, and specifically designed oral airways (such as the Berman airway).
The intubating LMA™ is an excellent conduit for tracheal intubation. It is used in Plan B of the DAS guidelines but can also be useful in the elective management of the known difficult airway and in patients with C-spine injuries. In the latter group, fluoroscopic and ultrasound studies have demonstrated decreased movement of the cervical spine with the ILMA than direct laryngoscopy with manual in-line stabilisation.1,2 The ILMA can be used for blind intubation, but should be used in conjunction with a fibre optic bronchoscope wherever possible, as fibre optically guided techniques are always superior to blind techniques.3
Fibre optic guidance is the gold standard, but when used correctly, blind techniques have a success rate of greater than 90%:
- Blind insertion in patients without difficult airways: 95.7%.4
- Blind insertion in patients with known or anticipated difficult airways: 64% first pass, 92% overall, other 8% achieved with fibre optic technique.5
- In unanticipated difficult airways: one study of 23 patients – 75% first pass blind insertion, 100% overall insertion.5
- Using the blind technique, oesophageal intubation may be up to 5%.6
- Fibre optic technique improves first attempt success rate,5 overall insertion success rate,7 and nearly always succeeds when blind technique fails.8
A learning curve of about 20 insertions has been described,9 and studies with novice users suggest that high success rates can be achieved with minimal training.10,11
Standard Portex or Mallinckrodt PVC tubes can be used successfully with the device,12 and if used, should be inserted in the reverse orientation (against their natural curve), as this decreases the angle of emergence of the device and improves insertion rates.13
In contrast to the ILMA, blind success rates with other LMAs are low,14,15 but can be improved to 90-100% with fibre optic guidance.7,16
There are many examples in the literature of successful difficult airway management using the Aintree Intubating Catheter™ (AIC) in combination with the classic LMA™ and Proseal LMA™.17,18 Evidence suggests that passage of the AIC via the Proseal LMA™ is as easy and reliable as via the classic LMA™.19 The Supreme LMA™ does not seem to be suitable for this purpose as the angle of exit of the AIC from the device is unpredictable due to the epiglottic fins in its bowl.20
After successfully inserting a tracheal tube through an LMA, it is tempting to try to remove the LMA, leaving the tube in place. This is not recommended,21 except in the case of the intubating LMA, as this device is specifically designed to be removed, and comes with a stabilising rod to facilitate the procedure. During anaesthesia for surgery, the LMA is very unlikely to cause harm.22 If intubation is to be prolonged, an airway exchange catheter can be used to facilitate LMA removal.