Although we call this technique 'intubation through a laryngeal mask' this is not completely accurate since the endotracheal tube is not actually passed through the laryngeal mask with the technique described here. Rather an Aintree intubation catheter is advanced through the laryngeal mask into the trachea under fiberoptic guidance, the laryngeal mask is then removed, and finally the endotracheal tube is 'railoaded' over the Aintree catheter into the trachea.
There are certain advantages and disadvantages for both techniques:
This technique can be useful in a number of situations. 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 the following:
2. A flexible fiberoptic bronchoscope
3. Lubrication (either gel or- better- a silicon-based spray)
4. A laryngeal mask
Laryngeal masks of the 'classic' design, such as the LMA Unique®, are the easiest ones to pass a fiberoptic scope/ Aintree catheter assembly through. The 'classic' laryngeal mask has also the highest success rate of all design variations when used as a resue device in a 'can't-intubate-can't-ventilate' scenario.
Size obviously matters here and an Aintree catheter will clearly fit much easier through a bigger laryngeal mask. Note that the Aintree can get 'stuck' in a size 3 LMA Unique®.
We'll go through the technique (for right-handed practitioners) in a step-wise approach:
1. Prepare your equipment
Generously cover the outsides of the flexible fiberoptic scope and the Aintree catheter with a silicone-based lubricant spray.
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
Load the Aintree intubation catheter onto the flexible fiberoptic scope and tape the catheter to the fiberoptic scope to prevent it from moving back and forth and ensure that the bending section of the scope has an unrestricted range of movement. Trying to forcefully flex the scope when its bending section is covered by the Aintree catheter can result in (costly) damage to the scope.
While cutting and removing the aperture bars of the laryngeal mask allows for a) easier advancement of the Aintree catheter through the laryngeal mask and b) easier removal of the laryngeal mask over the Aintree catheter, this is not really necessary for success. In fact, it is a good idea to practice this method without removing the aperture bars, since this would reflect 'real-life' use of the technique in a CICV scenario ( you would not want to remove the laryngeal mask to cut aperture bars and then re-insert it if this was your only working rescue device!
Connect the swivel adapter to the laryngeal mask and breathing circuit. This will allow ongoing oxygenation and delivery of inhalational anesthesia through the laryngeal mask while you are navigating the scope/ Aintree catheter assembly into the patient's trachea.
2. Pre-oxygenate your patient!
3. Advance the scope/ Aintree catheter assembly into the patient's trachea
Feed the scope/ Aintree catheter assembly throught the side port of the the swivel adapter, down the laryngeal mask, through the vocal chords into the patient's trachea. Stop when the tip of the fiberoptic scope is just above the carina.
Note and remember the centimeter mark of the Aintree intubation catheter at the level of the patient's teeth. The centimeter length marks of the Aintree catheter can be seen through the laryngeal mask wall.
4. Do not remove the fiberoptic scope now!
It is tempting to pull out the fiberoptic scope now that you have visualized the carina and therefore confirmed that the tip of the Aintree catheter is located well within the trachea. We would suggest to leave the fiberoptic scope in-situ and maintain a constant view of the carina or al least tracheal rings as you perform step 5.
If you perform this technique solo, it is a good idea to put the scope down on the patients chest and free your hands up for step 5, i.e. withdrawing the LMA with one hand and maintaining the Aintree catheter position with the other, all the while checking that the scope is still in the trachea!
5. Withdraw the laryngeal mask
Gently withdraw the laryngeal mask from the patient's airway with your left hand while keeping the Aintree catheter in a steady position and maintaining a view of the carina/ tracheal rings with the fiberoptic scope in your right hand. Avoid pulling out the Aintree catheter with the laryngeal mask! This is especially important given the relative shortness of the Aintree catheter. It can easily slip out of the airway!
Leave as much of the scope/ Aintree catheter assembly in the airway as you can.
You now lost the ability to oxygenate and anesthetize your patient through the laryngeal mask!
'Un-tape' the Aintree catheter from the scope with your left hand.
Now grasp the Aintree catheter with your left hand at the level of the patient's teeth. Check one last time that the fiberoptic scope's view is still that of the carina. Also check the centimeter marking on the Aintree catheter to confirm that it has not significantly moved out of the airway when you were withdrawing the laryngeal mask.
Now pull out the fiberoptic scope (with your right hand) while never letting go of the Aintree catheter! Always keep hold of the catheter at the patient's teeth with you left hand!
Pull the laryngeal mask off the Aintree catheter.
6. Pass the endotracheal tube
This step is much the same as for intubation with a gum-elastic bougie.
Feed or ask an assisstant to feed the endotracheal tube onto the Aintree catheter. Use lubricant gel for the distal portion/ cuff section of the ET tube.
Grab the end of the Aintree catheter and 'railroad' the ET tube over the Aintree catheter into the trachea. Again, be careful not to accidentally pull back the Aintree catheter and come out of the airway!
TIPS, TRICKS AND TROUBLESHOOTING
- Smaller is better! Use the smallest ET tube possible, i.e. a size 7.0 or even 6.5mm ID, which will fit (only just) over an Aintree catheter to minimize the gap between the ET tube and the catheter and reduce the risk of the tube getting cought at the arytenoids.
- Keep the fiberoptic scope bending section in a neutral position when withdrawing the scope from the Aintree catheter to avoid causing damage to the scope.
- Consider using a laryngoscope for pharyngoscopy if you have a hard time advancing the ET tube off the Aintree catheter.
- It is possible to oxygenate your patient with an Aintree catheter using either of the two Rapi-Fit adapters supplied with the kit for apneic oxygenation or jet-ventilation with EXTREME CAUTION (aka high risk of pneumo/barotrauma).
The most likely/ common problem encountered is that the ET tube does not pass off the Aintree catheter, i.e. get's 'stuck' at the laryngeal level.
- Try a smaller ETT (see above)
- Try to advance the ET tube with very gentle pressure while constantly rotating it (corkscrew maneuver)
- Use generous amount of lubricating gel for the tip and cuff of the ET tube
- Try a Parker Flex-Tip ETT
The tapered tip of the Parker Flex-Tip ETT reduces the 'step-up' between the Aintree catheter and endotracheal tube, allowing for easier passage past the vocal chords