Cricoid force: time to put it to one side.

Anaesthetists have come to accept the use of cricoid force as a part of professional practice, with 92% reporting they use it for all emergency operations and the remaining 8% saying they will use it if they consider their patient at significant risk of regurgitation and aspiration (e.g. in cases of bowel obstruction) 10. Notwithstanding this, some anaesthetists find it difficult to understand how it became and remains a consistent part of modern anaesthetic guidelines and practice despite only being backed by a ‘preliminary communication’ of an albeit well-constructed single-centre case series of 26 cases from a single anaesthetist in 1961 11. Diffusion of innovations theory 12 can help to explain the phenomenon of why some things catch on and others do not – broadly, diffusion and adoption of novel products, techniques and behaviours does not depend on evidence but is more akin to a social movement (in which evidence plays a variable part). The interpretation of the legal position by anaesthetists varies, with Levy 13 persuasively challenging the interpretation by Turnbull et al. that ‘courts appear to favour the use of cricoid pressure’ 7. Levy refers to ‘Common law authority in respect of not implementing a particular intervention’ and he concludes that following an aspiration event ‘an anaesthetist's actions will be evaluated in the context of the totality of the preventative measures taken to prevent aspiration.’ Against this background there is an understandable reluctance to abandon an intervention that many believe to be beneficial, so a pragmatic way forward would be to find a replacement that matches the potential advantages of cricoid force but has fewer disadvantages. Gautier et al. compared the effects of cricoid force vs. force applied to the lower left paratracheal oesophagus and in their study they have demonstrated a significant decrease in oesophageal diameter using paratracheal compression and, importantly, also reported a decrease in air entry into the gastric antrum during facemask ventilation using this manoeuvre. We need to consider what conditions would have to be fulfilled in order to help us decide whether we should change our practice and adopt paratracheal compression into our risk reduction strategy against aspiration of gastric contents. By demonstrating that gastric insufflation (which is associated with regurgitation) is reduced to a greater extent when using paratracheal compression than when using cricoid force, Gautier et al. have started us on this journey. They have built on the existing research base into the anatomical basis of prevention of regurgitation which over the last 20 years has demonstrated that the mechanism is likely related to occlusion of the pharynx, and that the oesophagus is displaced laterally during cricoid pressure 14-16. Most recently, Andruszkiewicz et al. compared the impact of cricoid pressure vs. a novel technique of paralaryngeal pressure on the anteroposterior diameter of the oesophagus and concluded that cricoid force does not decrease the diameter of oesophagus but that paralaryngeal force does 17. Gautier's group adopted a sensible approach, starting by asking just one question in their first paper on the topic – ‘can we occlude the oesophagus more reliably a little lower down?’ As well as answering that question, they have identified in their discussion most of the future work that needs to be done to complete the necessary evidence base. They recognise that their study would need to be repeated with patients receiving neuromuscular blocking agents and acknowledge that data would need to be collected in obese patients, in patients with potential difficult airways and using a variety of airway pressures during facemask ventilation. Other studies that have been carried out over the years using cricoid force would need to be replicated with paratracheal compression, such as the ability to prevent regurgitation with increasing oesophageal pressures in cadaveric studies, the effect on airway patency and ease of facemask ventilation/tracheal intubation, how it influences placement of SADs and whether it changes the view at laryngoscopy 18-24. Most of these studies would be easy to reproduce and could be completed relatively quickly, such that the profession could have an evidence base for non-inferiority of this technique 25 within a few years. A randomised controlled trial of the two techniques would most likely be deemed impractical due to the huge sample size required (based on the incidence of serious aspiration and the number of rapid sequence inductions performed each year). A national aspiration registry (assuming that one could even be established) would not be able to provide a definitive answer regarding the comparative safety and efficacy of cricoid force and paratracheal compression as denominator data for the two techniques would be unknown. The way forward in the 21st century may be to adopt a philosophical and ethical approach to the problem. There is a Royal College of Anaesthetists airway lead in virtually every NHS trust in the UK (personal communication, A McNarry) and part of their role, highlighted in an indicative job description, is to ‘ensure best practice in the management of patients at risk of aspiration’. The Difficult Airway Society reported in their Autumn 2017 newsletter that they are forming a working group to look at ‘guidance on the ethics of airway management’. Gautier has provided us with a scientific explanation for a mechanism of action for paratracheal compression in the prevention of regurgitation, and if we can develop an evidence base for non-inferiority (or superiority) of this technique compared with cricoid force in relation to adverse effects, the Difficult Airway Society could adopt a stance that it was ethical to use force to the left paratracheal oesophagus in place of cricoid force as part of our risk reduction strategy against aspiration. The ethical debate would have to consider the possible unintended consequences of a change in practice, such as the potential for carotid artery compression, and also consider situations where the technique may have unanticipated failure modes such as achalasia (where the oesophagus could be filled with semi-solid material higher up than the site of compression) or situs inversus (where the oesophagus may lie to the right of the trachea). Individual airway leads could then, after training their operating department practitioners and anaesthetic nurses appropriately, change their departmental standard operating procedures. As the evidence base develops, case reports of success and failure of paratracheal force in clinical practice will start to emerge. These will undoubtedly attract attention but reporting bias and publication bias will limit their overall value in determining the relative safety and efficacy of this new oesophageal compression manoeuvre. If we imagine an alternate universe where Sellick had described paratracheal compression in 1961, it is possible that we may all have been using this technique routinely for patients at risk of aspiration for the last 65 years, and oesophageal compression with an assistant's thumb placed to the left of the trachea, cephalad to the clavicle and medial to the sternocleidomastoid muscle would be the norm. When considering the use of force to the front of the neck to decrease aspiration risk, in the future, there may not be a need to abandon cricoid force altogether but simply to put it to one side. No external funding and no competing interests declared.