Dr. Braude is an assistant professor of emergency medicine at the University of New Mexico School of Medicine, the medical director of PHI Air Medical of New Mexico, both in Albuquerque, a co-director of the Emergency Airway Training Program at the University of New Mexico, and a co-director of the National Procedural Sedation Course.
A 58-year-old woman arrives at a community ED with a severely impaired mental status secondary to polysubstance overdose. The emergency physician elects to perform rapid sequence intubation for airway protection and assisted ventilation. The patient is preoxygenated without positive pressure ventilation, placed in the sniffing position, and cricoid pressure is applied by a new respiratory therapist after the patient receives 100 mg of rocuronium and 30 mg of etomidate.
The physician is unable to visualize the vocal cords and saturations begin to fall. bag-valve-mask ventilation is attempted with continued cricoid pressure, but there is little lung rise and the saturations drop. At this point, a senior respiratory therapist arrives and suggests that cricoid pressure be reduced. Ventilation improves with subsequent rise in oxygen saturation. The emergency physician reattempts laryngoscopy without cricoid pressure and is successful.
Cricoid pressure is the application of force, optimally 30 to 40 Newtons (Can J Anaesth 1997;44:414), to the front of the cricoid cartilage with the intent of occluding the esophagus between the back of the cricoid ring (the only complete ring in the trachea) and the anterior surface of the spinal column. Cricoid pressure was described as early as the 1700s, and was originally intended to prevent air from entering the lungs during positive pressure ventilation. (Anesth Analg 1974;53:230.) It gained widespread modern usage during the 1960s as a means of preventing aspiration during rapid induction of anesthesia in patients with full stomachs, based on a landmark article by Sellick. (Lancet 1961;2:404.) Cricoid pressure naturally made its way into the emergency department with the introduction of RSI, and is now included as a mandatory step in all the major emergency medicine texts (Tintinalli, Rosen, Harwood-Nuss). It has subsequently become a part of optimal bag-valve-mask ventilation as well. (J Emerg Med Services 2005;30:46.)
Surprisingly, there is little evidence that cricoid pressure actually prevents aspiration or gastric insufflation. The original paper by Sellick described only 26 cases where it was used and in three cases there was reflux on release of cricoid pressure “…suggesting that in these three cases, cricoid pressure had been effective.” (Lancet 1961;2:404.) The remaining studies are well summarized by Brimacombe and Berry in their excellent review of cricoid pressure. (Can J Anaesth 1997;44:414.) There is similar evidence to support the use of cricoid pressure during bag-valve-mask ventilation of adult and pediatric patients but less so if the patient was difficult to ventilate. (Br J Anaesth 1987;59:315; Anesthesiology 1993;78:652; Anaesth Intensive Care 1988;16:139.)
There is significantly more evidence that cricoid pressure may cause harm in a variety of ways. Most ironic are the papers that demonstrate cricoid pressure may actually predispose to aspiration by reducing lower esophageal pressures. (Anaesthesia 2004;59:435; Anesthesiology 1997;86:7.) There are also two papers that demonstrate the esophagus does not lie directly behind the trachea in a position amenable to compression with cricoid pressure in about half of the population. (Can J Anaesth 2002;49:503; Anesthesiology 2003;99:60.) Applying cricoid pressure further increased the displacement of the esophagus from behind the trachea. Cricoid pressure may also cause partial or complete obstruction of the airway lumen, even at normal force. (Anesthesiology 2003;99:60; Anaesthesia 2000;55:208; Anaesthesia 2000;55:260.) Furthermore, cricoid pressure may induce a reflex vasopressor response which, in patients with elevated ICP or cerebrovascular or coronary artery disease, may be worse than the potential benefits. (Anesth Analg 2001;93:78.)
It also has been clearly demonstrated that cricoid pressure may impair laryngeal exposure at laryngoscopy, potentially to the point of complete obscuration. Cricoid pressure was never intended to improve the view of the airway though this misconception is widespread in my experience. Haslam et al studied the effects of increasing cricoid pressure on 40 patients undergoing elective surgery. While they identified a range of effects, it is most important to note that the view deteriorated in 24 patients, three of whom had complete loss of view. The authors note, “We conclude that the effect of cricoid pressure on laryngoscopy is complex. However, in some individuals, a force close to that currently recommended (30 N) may cause complete loss of glottic view.” (Anaesthesia 2005;60:41.)
Levitan and colleagues recently reported that the glottic view was as likely to worsen as improve with cricoid pressure and that in three percent the view was completely obscured. (Ann Emerg Med 2006;47:548.) The take-home message is that the intubator must be aware of the potential for cricoid pressure to worsen and the potential to completely obscure the laryngeal view. In these cases, cricoid pressure must be reduced or released. If the glottic view remains suboptimal, external laryngeal manipulation (bimanual laryngoscopy), a technique that is distinct from cricoid pressure, should be performed.
If that were not enough, cricoid pressure is also remarkably difficult to apply correctly. Studies in the ED and OR demonstrate consistently poor technique. (Emerg Med Australas 2005;17:376; Anesth Analg 1996;83:859.) Cricoid pressure should obviously be applied to the cricoid membrane, but inexperienced assistants (and sometimes experienced ones) will often reach instead for the most obvious landmark in the neck, the thyroid cartilage, and therefore must be closely supervised. In the ED, the one-hand technique makes the most sense using about 40 N of force once induced. This can apparently be approximated by compressing a capped 50 cc syringe to the 30 cc mark, which is a worthwhile exercise for the entire ED team involved in airway management. (Eur J Anaesthesiol 2000;17:443.)
Pending more conclusive data, cricoid pressure should be applied during any positive pressure ventilation. If ventilation is difficult, the assistant maintaining cricoid pressure should try reducing it. If the patient vomits, cricoid pressure should be released to prevent potential esophageal rupture as demonstrated in one case report. (Anaesthesia 1991;46:40.) Cricoid pressure should probably be applied during RSI as well, from the time of drug administration to tube confirmation, as long as the laryngeal exposure is adequate. In the event the intubator cannot visualize the cords, cricoid pressure should be reduced and if the view remains inadequate cricoid pressure should be released completely and the assistant should slide his hand up to the larynx to assist with external laryngeal manipulation.
Given the balance of evidence, I doubt cricoid pressure would gain acceptance if it were introduced today, but by precedent it is probably here to stay for the foreseeable future. It is perhaps more important during bag-valve-mask ventilation than during RSI where the benefits are more clear and the downsides (particularly obscuring view of the cords) are less relevant. That being said, it is worth knowing how to do it correctly: not too hard and not too soft. And it is even more important to know when not to use it than when to use it, namely when your view of the larynx is inadequate.