The relationship between the diameters of the adult cricoid ring and main tracheobronchial tree: a cadaver study to investigate the basis for double-lumen tube selection.

OBJECTIVE: Previous investigation of the adult cadaver larynx has shown that the cricoid diameter never exceeds that of the glottis. This further analysis looks at the anatomic relationships between the diameter of the cricoid ring and those of the main tracheobronchial tree to discover how they relate to double-lumen tube selection. DESIGN: Prospective. SETTING: A city mortuary. PARTICIPANTS: Adult cadavers undergoing autopsy. INTERVENTIONS: The trachea was partially transected above the first ring to expose the cricoid cartilage from below and was then further opened with a progressive longitudinal incision to allow access to the tracheobronchial tree. MEASUREMENTS AND MAIN RESULTS: In 59 male and 49 female white cadavers, the largest of a graduated series of cylindrical sounds that the cricoid ring would accommodate was noted. They were then used to measure the maximum diameters of the main tracheobronchial tree. In both sexes, the mean diameter of the cricoid was shown to be the same as that of the left main bronchus, the left main bronchus to cricoid ratio almost invariably exceeded 83% (against the maximum double-lumen tube tip-to-body ratio of 80%), and the coefficient of correlation (r) between the cricoid and left main bronchial diameters was 0.6. For the trachea and left main bronchus, r was 0.5 in male cadavers and 0.45 in female cadavers. CONCLUSIONS: The dimensions of the cricoid ring best define those of the main bronchi. Knowing its diameter should assist anesthesiologists with double-lumen tube selection.

A cadaver study to measure the adult glottis and subglottis: defining a problem associated with the use of double-lumen tubes.

OBJECTIVE: To test the hypothesis that the adult cricoid diameter is the same or less than that of the glottis. DESIGN: Prospective. SETTING: A city mortuary. PARTICIPANTS: Adult cadavers undergoing autopsy. INTERVENTIONS: After removal of the organs, the trachea was opened above the first ring to allow access to the cricoid from below, and the cricothyroid membrane was cut so that passage of measuring sounds through the vocal cords from above could be confirmed. MEASUREMENTS AND MAIN RESULTS: In 79 male and 55 female cadavers, the largest of a graduated series of cylindrical sounds that the cricoid ring would accommodate was noted. Then the biggest size possible that could pass through the glottis was measured. Height and weight were recorded. In 68% of males and 76% of females, glottic diameter was greater than subglottic; in all other cases, it was the same. In none was it smaller. Correlation between height and cricoid diameter was 0.24 for male cadavers and 0.21 for female cadavers. Regression analysis showed females to average a cricoid diameter 3.5 mm less than males of the same height. CONCLUSIONS: The ruling diameter of the adult larynx is not the glottis but the cricoid ring. Its correlation with height is extremely poor, and it averages 3.5 mm less in females than males of the same height. These findings are important for thoracic anesthesiologists.