The effect of cricoid pressure on the cricoid cartilage and vocal cords: an endoscopic study in anaesthetised patients.

Cricoid pressure is used to protect the lungs from contamination with gastric contents during tracheal intubation. We studied the effect of cricoid pressure applied with a yoke on 30 anaesthetised patients examined fibreoptically through a laryngeal mask airway. We assessed the effect of 20, 30 and 44 N on the internal appearance of the cricoid and vocal cords. Difficulty in ventilation was also recorded. At 44 N, cricoid deformation occurred in 27/30 patients (90%) and 15/30 (50%) had cricoid occlusion [13/30 (43%) had cricoid occlusion at 30 N and 7/30 (23%) at 20 N]. Associated difficulty in ventilation was present in 15 patients (50%) and 18/30 (60%) had vocal cord closure with associated difficult ventilation, at forces up to 44 N. Cricoid occlusion was unrelated to age and body mass index but females were at greater risk. Orthodox values of cricoid pressure, applied with a yoke, may produce obstruction at the level of the cricoid cartilage or vocal cords, with implications for tracheal intubation and ventilation by mask.