This technique uses a laryngeal mask as a conduit for placing a microlaryngoscopy tube (MLT). Although this technique can be performed blindly, it is more easily done with fiberoptic guidance.
Note that with this approach the laryngeal mask remains in-situ until extubation and cannot be removed over the MLT.
There are certain advantages and disadvantages of this technique when compared with the intubating-through-a-laryngeal-mask technique with an Aintree catheter:
The indications for this technique are the same as intubating through a laryngeal mask with the Aintree catheter. The most clear-cut indication is this one:
A 'can't-intubate-can't-ventilate' (CICV) scenario when a laryngeal mask has been placed as a rescue device and works well enough to oxygenate the patient, but there is a need for endotracheal intubation and the patient cannot be woken up from anesthesia, i.e. surgery has to proceed and a laryngeal mask is not a sufficient airway for the case. A practical example might be a case of an emergent c-section for acute fetal distress under general anesthesia, where standard intubation has been impossible and oxygenation is (just about) possible with a laryngeal mask.
Other, somewhat 'softer' indications include the following (note that this technique would not necessarily be considered 'first choice' in these situations):
- After several unsuccessful intubation attempts with direct laryngoscopy
- After unsuccessful intubation attempts with videolaryngoscopy
- Elective use to train for using the technique in an emergent CICV scenario (see above)
- Intraoperative conversion from laryngeal mask to endotracheal tube, for example in cases...
- where anesthesia was started with a laryngeal mask but the device subsequently fails/ the seal fails
- when muscle relaxation becomes necessary and the practitioner does not feel confident to ventilate a paralyzed patient with a laryngeal mask in-situ
You will need:
- A size 4 laryngeal mask. Laryngeal masks of the 'classic' design, such as the LMA Unique®, are the easiest ones to pass a MLT/ fiberoptic scope through.
- A size 6.0 microlaryngoscopy tube (MLT). A smaller MLT will not accommodate a standard adult fiberoptic bronchoscpe.
- Lubricant, preferably a silicon-based spray.
- A fiberoptic bronchoscope
The reason why this technique requires a microlaryngospy tube is that a 'standard' size 6.0 ET tube is simply not long enough to fit through a laryngeal mask and reach subglottically.
The MLT on the other hand, when fully advanced down a laryngeal mask, has more than enough clearance distally to the laryngeal mask to be placed safely below the vocal chords as the picture below illustrates.
1. Prepare your equipment
First cut the aperture bars on the laryngeal mask. Whilst doing this helps when it comes to 'railroading' the MLT into the trachea, cutting the aperture bars is not strictly necessary. The MLT can be advanced past uncut aperture bars (the aperture bars of the LMA Unique are fairly flexible).
Lubricate the fiberoptic bronchoscope and the MLT. The most likely part to get stuck inside the laryngeal mask is the cuff of the microlaryngosopy tube.
Lubricating gel can also be used but has two disadvantages: It can get sticky once it starts drying up and it is more likely to mess up the optics of your fiberoptic scope if it contaminates its tip.
2. Insert the MLT into the laryngeal mask
Insert the MLT into the laryngeal mask so that the tip of the MLT sits just above the cut aperture bars. This position corresponds to the 20 cm length marking of the MLT lining up with the connector of the laryngeal mask.
With the laryngeal mask placed into the airway it is now possible to ventilate/ oxygenate your patient by connecting a breathing system to the MLT standard tube connector (just like a 'normal' laryngeal mask would be used). Inflating the cuff of the MLT is often not even necessary as the fit between the MLT and the laryngeal mask is already pretty snug.
3. Fiberoptic guidance
Advance the fiberoptic bronchoscope throught the MLT to its tip and visualize the vocal chords. Further advance the fiberoptic scope into the patient's trachea.
4. Endotracheal intubation
'Railroad' the MLT off the fiberoptic scope to an appropriated depth. Check the MLT length markings at the lips.