troubleshooting supraglottic Airway INsertion
As with the other lifelines, interventions to optimise attempts at achieving alveolar oxygen delivery via a supraglottic airway should be targeted towards the factors impeding success. The challenges arising with supraglottic airway insertion can be categorised under three headings:
- Entry: inability to insert the supraglottic airway into the mouth due to factors such as limited mouth opening or excessive muscle tone.
- Passage: difficulties in getting the supraglottic airway to negotiate the pathway through the pharynx to reach the larynx.
- Seating: misalignment of the laryngeal orifice and the laryngeal inlet (leading to obstruction or gastric insufflation) or inadequate seal of the cuff of the supraglottic around the laryngeal orifice (leading to leak around the cuff and inability to generate sufficient pressure to allow alveolar ventilation).
best effort at supraglottic airway
The process of optimisation for supraglottic airway differs somewhat from that of the other lifelines. Sequential attempts to establish alveolar oxygen delivery using a endotracheal tube or face mask typically involve optimisation techniques being superimposed on one another producing incremental gains to improve the view of the larynx during intubation or the patency of the airway during face mask ventilation. Whilst such escalating optimisations targeted towards the specific issues impeding alveolar oxygen delivery also occur when using a supraglottic airway, a significant number of optimisations targeted at passage of a supraglottic airway involve alternative rather than incremental strategies. The significance of this is twofold:
- Firstly it means that previous attempts at passage of a supraglottic airway may provide limited information about the likelihood of success at subsequent optimised attempts (beyond identifying the nature of the problem - entry, passage or seating - and ensuring interventions are selected that will impact on this issue). For example, if a supraglottic airway 'holds up' trying to negotiate the turn at the posterior oropharynx into the laryngopharynx when passed conventionally, beyond an awareness that they are frequently useful techniques to overcome this problem in general, no information is usually gained that would allow the airway clinician to predict the likely impact of using a different type of supraglottic airway or inserting the supraglottic airway backwards in that particular patient. This is different to the situation during laryngoscopy in which the view obtained with one laryngoscope blade may provide important information about the likely impact of using an alternative blade. This informs the decision about the best intervention to further optimise the airway on a subsequent attempt and in some situations may help decide whether further attempts are warranted at all.
- Secondly it means that there are key optimisations for supraglottic airway that cannot be implemented simultaneously during the same attempt but instead necessitate separate attempts. For example, although optimisations such as positioning and muscle relaxation can (and should) be superimposed during a single attempt, the introduction of a supraglottic airway using both conventional and reversed orientation clearly requires two separate attempts.
The above two factors conspire to make it more difficult to achieve a best effort at supraglottic airway insertion in under three attempts, particularly in the situation in elective anaesthesia where a supraglottic airway is the intended primary airway and for surgical reasons a type, other than that with which the airway operator is most confident, is used on the first attempt. Thus taking the example of induction of anaesthesia for oral surgery: if a reinforced supraglottic airway was used on the first attempt but could not be passed around the back of the oropharynx, attempts with a standard supraglottic airway using both conventional and reversed orientation of the device would typically be reasonable before declaring a best effort. Whilst other optimisation interventions such as positioning and muscle relaxation should also be superimposed during these successive attempts, the above example highlights that even with the most efficient implementation of all other optimisations, the high impact 'size/type' and 'manipulation of device' interventions that would be employed in this situation will in themselves require three attempts to implement. The result is that clinicians must be particularly aware of the need to rapidly escalate optimisations in order to achieve a best effort at supraglottic airway within the three attempt limit. This may be less of an issue when a supraglottic airway is used as a rescue device than as the intended primary airway, as in this situation the first attempt with supraglottic airway should made with the device with which the airway clinician feels most confident they will be able to achieve alveolar oxygen delivery.
The following table outlines the possible real-time optimisation interventions in pursuit of a best effort at supraglottic airway and the issues they target. Note that this table is intended as a foundation resource for training and not to be used during the process of airway management.
Use of a Laryngoscope to Optimise Supraglottic Airway Placement:
Inability to pass a supraglottic airway when entry of the device into the mouth is possible, typically results from the cuff of the device folding over on itself or from it pushing the tongue or epiglottis back and obstructing the airway. The use of a laryngoscope to assist with placement of a supraglottic airway is often not considered, but is able to overcome most of the issues associated with difficult passage by lifting the tongue and epiglottis forwards and creating a clear space into which the supraglottic airway can be placed - even if a view of the larynx cannot be obtained. Due to the high profile of the laryngoscope there is often limited space to insert the supraglottic airway in the midline but with practice (in non-emergency situations) it is usually easy to achieve entry via the left corner of the mouth. This is easier when a device without a fixed curve in the stem is used (e.g. classic or proseal LMA or iGel). A useful strategy is to leave the laryngoscope in situ following the last attempt at endotracheal tube and immediately attempt placement of the supraglottic airway with laryngoscope assistance. A device known as a 'tongue anterioriser' is also available that performs a similar function to the laryngoscope but without providing any view into the pharynx (which is not required for this technique). The advantage of the tongue anterioriser is that it is flat, this lower profile making it less likely that it will will obstruct entry of the SGA into the mouth.
Use of a Bougie to Optimise Supraglottic Airway Placement:
As a rescue technique, the deliberate passage of a bougie into the oesophagus followed by railroading of a second generation supraglottic airway over the bougie via it's oesophageal lumen, is well described. The technique is mentioned in the 2015 Difficult Airway Society Guidelines where it is described as having a 100% success rates on the first attempt (superior to success rates using digital insertion or insertion using the Proseal introducer) when performed using a Proseal LMA in some studies. The rationale is that the bougie guides the oesophageal opening on the tip of the SGA to the oesophagus, which in turn better aligns the oesophageal lumen with the laryngeal inlet. This technique is likely to be more difficult with some designs of LMA and so requires practice with the device being used in a non-emergency situation. As there is a risk of trauma from oesophageal passage of the bougie it should only be attempted as a rescue technique. This technique can be combined with the use of a laryngoscope as described above, passing first the bougie, then the supraglottic airway with the laryngoscope in situ.