Cricoid force: therapeutic, prophylactic or routine

Higgs and El-Boghdadly distinguish between prophylactic cricoid force, applied to help prevent regurgitation of gastric contents in at-risk patients, and therapeutic cricoid force, applied to help reduce further regurgitation once it has already occurred [1]. They suggest that clinicians reluctant to apply cricoid force prophylactically might still consider applying it therapeutically. Yet it stands to reason that to consider applying cricoid force either prophylactically or therapeutically, a clinician must believe that it might be effective in limiting regurgitation. Given the only potential harms of properly applied cricoid force can be readily rectified by simply removing it if they are encountered, in an at-risk patient it would be illogical for such a clinician to wait until gastric regurgitation (and potential pulmonary aspiration) has already occurred before applying it. Conversely, the potential merits of therapeutic application of cricoid force as part of the management of gastric regurgitation in patients not previously identified as being at increased risk are acknowledged. While there are no randomised controlled trials supporting the efficacy of cricoid force in preventing pulmonary aspiration of gastric content, this is true of all the variously touted elements of rapid sequence intubation. Despite being a major cause of airway-related death, the low incidence of aspiration makes adequately powering randomised controlled trials of preventative strategies challenging [2]. Thus, many commonly cited elements are based solely on the questionable rationale that there is a proportional relationship between the risk of aspiration and the interval between loss of airway protective reflexes and the inflation of a cuff in the trachea [3]. In contrast, the premise for the use of cricoid force is that it compresses the post-cricoid hypopharynx, preventing passage of material between the stomach and pharynx, a mechanism for which there is experimental evidence [2]. In 1961, Sellick showed that when the stomach of a cadaver was filled with water, cricoid force not only prevented regurgitation of fluid into the pharynx when the cadaver was placed into steep Trendelenburg tilt, but that the flow of water into the pharynx could be modulated by altering the force applied [4]. Sellick also showed by passing a latex tube filled with contrast medium to a pressure of 100 cmH2O into the oesophagus of an anaesthetised patient, that cricoid force obliterated the oesophageal lumen [4]. More recently, a study examining the impact of cricoid force on the ability to pass a gastric tube and videolaryngoscopic visualisation of oesophageal patency in anaesthetised patients was terminated prematurely. This was when application of cricoid force prevented passage of the gastric tube and visually occluded the oesophageal opening in all patients, whereas the gastric tube passed with ease and oesophageal patency was visually observed in all patients when it was not applied [5]. There are also studies showing that cricoid force prevents gastric insufflation and impedes placement of a supraglottic airway [2], further supporting that it compresses the oesophageal entrance. Moreover, unlike cricoid force, other elements of a rapid sequence induction have much more serious potential harms, such as anaphylaxis, awareness and cardiovascular collapse [3], that cannot simply be reversed if encountered. It is perverse that cricoid force has been abandoned selectively by many clinicians for not representing evidence-based practice when, compared with most other commonly retained elements of a rapid sequence induction, it is cost-free, better reasoned, has less potential for harm and more evidence of efficacy. For clinicians who have abandoned cricoid force on this basis, the question to be answered is why they employ any element of rapid sequence induction at all. Rather than selectively abandoning cricoid force as a component, it should perhaps be the only component we retain. Given that even low-risk patients apparently lacking risk factors still sometimes regurgitate gastric content, it could be argued that we should be encouraging routine application of force during all tracheal intubations, independent of the risk of regurgitation, rather than sanctioning its therapeutic use in at-risk patients. The increased opportunities for training and practice this would provide would also help address the common complaint that cricoid force is improperly performed, perhaps further improving its efficacy.