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The cannula eFONA approach: a viable alternative?

2019; Wiley; Volume: 75; Issue: 1 Linguagem: Inglês

10.1111/anae.14888

1365-2044

Umair Ansari, Tim Davies,

Cardiac Arrest and Resuscitation

We would like to congratulate and commend Rees et al. for their thought-provoking, high-fidelity study on the delivery and assessment of emergency front-of-neck access (eFONA) 1. However, we would appreciate further clarification regarding some of the study limitations. Firstly, the participants’ prior experience in eFONA techniques is not described. The majority of participants were recruited from the Monash Hospital network and we wonder whether familiarity with a cannula technique may have contributed to an overestimation of the beneficial effect of the cannula technique compared with the other. We understand the course was based on the ‘cannot intubate, cannot oxygenate’ programme developed at the Royal Perth Hospital. In a previous study by Heard et al. 2 there was a reported success rate of 100% in achieving adequate jet ventilation using a scalpel bougie technique (SBT). There was an associated 20% failure to pass a size 6.0-mm I.D. tracheal tube (TT) over the bougie, due to not making the tract large enough to facilitate passage of the TT, with a successful mean time of 61 s to ventilation. In the study by Rees et al., a 35% failure rate was recorded using a SBT, with 53% of these due to incorrect placement of the bougie, leading to false passages. If the attempt was successful it took a mean time of 90 s. We understand the Perth group removed the oral TT before attempts at eFONA, whereas in the study by Rees et al., we understand that it was left in situ, and this may have contributed to the difference in both time taken and success rate. In the study by Rees et al., there was no specified tracheal space given to candidates, they were just encouraged to perform eFONA on the ‘high’ superficial part of the trachea. There were two attempts at SBT technique that had to be abandoned due to catastrophic bleeding, which could have been secondary to a lower approach, placing the scalpel in the vicinity of the thyroid gland and its associated vessels. This could reflect a difference in identifying landmarks between the models used and human anatomy. As mentioned in the limitations section, a cognitive error may exist based on the methodology of the study. This occurs when in each case the needle cricothyroid puncture was performed first and subsequent operators may have been lured into performing the next procedure in the same place, due to a successful previous attempt, despite the trachea and skin being quite mobile in sheep and therefore the skin no longer overlying the trachea. The trachea of a sheep has a reduced distance between tracheal rings which might result in a higher rate of success with a technique that requires a smaller window to advance the tracheal component of the eFONA. We also noticed that this was a scalpel tracheostomy, not a scalpel cricothyroidotomy and reduced space between tracheal rings in sheep would possibly have made it more difficult to insert a bougie and favoured a needle technique, while also increasing the incidence of distortion of the trachea while railroading the TT over the bougie. In previous studies, including the Difficult Airway Society guidelines 3, a SBT technique is advocated as, if successful, it provides the safest technique to deliver oxygen, and time to oxygen delivery is very important in this situation. We were, therefore, intrigued that the study by Rees et al. did not clearly define time to oxygen delivery. We assume that it was when chest movement occurred, but this is not clear from the manuscript. The most common cause cited for failure with SBT was para-tracheal placement of the bougie. We feel that this may be related to the mobility of the tracheal structures in sheep and the diameter of sheep tracheas. The importance of the bougie entering the midline is paramount for a successful SBT and it is unclear from the study whether a sheep trachea is directly comparable to a human trachea. We noticed that in eight cases there was a second attempt at cannula insertion. Was it the same operators who then went on to have difficulty in SBT and if so was it because they struggled with eFONA, or that the second cannula attempt had distorted the anatomy, leading to difficult SBT? Also was there any difficulty with SBT in cases where emphysema or bleeding had already been caused by the cannula technique? Hamaekers and Henderson stated that there was no best method for eFONA and recommended that all anaesthetists should learn to perform more than one method for eFONA, as different situations require different techniques 4. Overall, we feel that this was a very interesting study and one which helps us begin to appreciate the different techniques available to us for eFONA.