Cricoid pressure: should we lay off the pressure?

We read with great interest the editorial by Calder and Yentis questioning what is in essence ‘safe practice’ [1]. We feel this could also bring into question the use of cricoid pressure. Although being described as far back as the 18th century it was Sellick who reintroduced it in 1961 as a means of preventing aspiration during the induction of anaesthesia [2]. Despite the introduction of cricoid pressure, aspiration still occurs and there is little evidence that it has improved patient outcome [2, 3]. In Sellick’s description of its correct application, patients were in a tonsillectomy position with their head and neck fully extended thus increasing the anterior convexity of the cervical spine, stretching the oesophagus and preventing its lateral displacement [4]. CT and MRI studies on non anaesthetised volunteers have shown that in up to 50% of the subjects the oesophagus was viewed lateral to the cricoid ring and that cricoid pressure displaced it more laterally [5, 6]. This questions the view that in its current day practise, direct pressure on the cricoid ring, fully compresses the oesophagus. It is often performed ineffectively and may cause a degree of airway obstruction. Even when performed correctly, it may interfere with laryngeal mask airway insertion, laryngoscopy and success in intubation [7]. This interference with routine airway manoeuvres and therefore the potential failure to optimally manage the airway is often the cause of the morbidity and mortality rather than any aspiration itself [2]. It is not unusual for the anaesthetist to ask for the pressure to be eased off to improve laryngoscopic view, negating the so-called benefits of cricoid pressure. Is there a reasonable alternative? A 1959 study by Snow and Nun in which 606 high risk cases were induced with a 40° head up tilt (reverse Trendelenburg) without any cricoid pressure applied revealed only one case of regurgitation which was attributed to the under dosing of the muscle relaxant. The 40° head up tilt raises the larynx approximately 19 cm higher than the lower oesophageal sphincter, preventing passive reflux into the pharynx. The significance of this height was based on observations by O’Mullane who found that even with distension of the abdomen, the intragastric pressure did not rise above 18 cmH2O unless there was contraction of the abdominal wall [8]. Similarly, there were no cases of aspiration when using a similar approach for inducing 600 obstetric patients with a head up tilt [9]. There are some other benefits of this position. Compared to lying supine, the functional residual capacity and oxygen reservoir may be greater after preoxygenation. In more obese patients, it is easier to ventilate patient in head up tilt as there is less of an effect on lung compliance in this position. The effect of gravity on pregnant patients and those with large breast causes less obstruction to the blade insertion during laryngoscopy compared to lying supine. This is also a well recognised approach to the intubating morbidly obese. Perhaps there is some merit to this technique which was superseded by cricoid pressure back in the 1960s. Is it time we turned back the clock?