Cricoid pressure, first described by Sellick in 1961, is used to occlude the upper esophagus to reduce the aspiration of gastric contents during rapid-sequence intubation. Pulmonary aspiration of gastric contents occurs in three stages. First, gastric contents reflux into the esophagus when the lower esophageal sphincter relaxes. Esophageal contents then reflux into the pharynx when the upper esophageal sphincter relaxes. Finally, pulmonary aspiration of pharyngeal contents occurs after loss of laryngeal reflexes.

To briefly review, the cricoid cartilage is the only upper airway cartilaginous structure that is a complete ring. The esophagus begins at the lower border of the cricoid cartilage. Cricoid pressure replaces the function of the upper esophageal sphincter by compressing the lumen of the upper esophagus between lamina of the cricoid cartilage and the body of the sixth cervical vertebrae, preventing regurgitation of esophageal contents into the pharynx (the second phase of aspiration). The upper esophageal sphincter is formed anteriorly by the lamina of the cricoid cartilage and posteriorly by the cricopharyngeus muscle, which is attached to the lateral aspects of the cricoid cartilage. Upper esophageal sphincter tone is 40 mm Hg in awake patients and decreases to less than 10 mm Hg during induction of anesthesia. Regurgitation of esophageal contents into the pharynx occurs when the upper esophageal sphincter pressure is less than 25 mm Hg. Therefore, induction of anesthesia can decrease upper esophageal sphincter pressure sufficiently to allow regurgitation of esophageal contents into the pharynx. Cricoid pressure counteracts this reduction in upper esophageal pressure. It is important to note that other cartilaginous structures in the upper airway are u-shaped; mistakenly exerting pressure on these structures will be ineffective and possibly lead to airway damage or distortion during intubation.