A multicentre prospective cohort study of the accuracy of conventional landmark technique for cricoid localisation using ultrasound scanning.

Cricoid pressure is employed during rapid sequence induction to reduce the risk of pulmonary aspiration. Correct application of cricoid pressure depends on knowledge of neck anatomy and precise identification of surface landmarks. Inaccurate localisation of the cricoid cartilage during rapid sequence induction risks incomplete oesophageal occlusion, with potential for pulmonary aspiration of gastric contents. It may also compromise the laryngeal view for the anaesthetist. Accurate localisation of the cricoid cartilage therefore has relevance for the safe conduct of rapid sequence induction. We conducted a multicentre, prospective cohort study to determine the accuracy of cricoid cartilage identification in 100 patients. The cranio-caudal midpoint of the cricoid cartilage was identified by a qualified anaesthetic assistant using the conventional landmark technique and marked. While maintaining the patient in the same position, a second mark was made by identifying the midpoint of the cricoid cartilage using ultrasound scanning. The mean (SD) distance between the two marks was 2.07 (8.49) mm. In 41% of patients the midpoint was incorrectly identified by a margin greater than 5 mm. This error was uniformly distributed both above and below the midpoint of the cricoid cartilage. The Pearson correlation coefficient of this error with respect to body mass index was 0.062 (p = 0.539) and with age was -0.020 (p = 0.843). There were also no significant differences in error between male and female patients. Identification of cricoid position using a landmark technique has a high degree of variability and has little correlation with age, sex or body mass index. These findings have significant implications for the safe application of cricoid pressure in the context of rapid sequence induction.