Elongation of the trachea during neck extension in children: implications of the safety of endotracheal tubes.

UNLABELLED: During neck extension, the changes in distance between endotracheal tube (ETT) tip and carina may not be equal to the changes in distance between vocal cords and ETT tip because of tracheal elongation. These distances are directly related to extubation risk. Using a fiberoptic bronchoscope, the distance between ETT tip and carina was measured in the neutral position after full extension of the neck in 25 children (2-8 yr old) scheduled for elective surgery under general anesthesia. The tracheal length was then measured in the neutral position and after full extension. The distance between vocal cords and ETT tip was calculated as the tracheal length minus the distance between ETT tip and carina. After full extension, the tracheal length (7.97 +/- 0.85 cm) was increased by 0.95 +/- 0.43 cm, and the change in distance between vocal cords and ETT tip was -1.08 +/- 0.47 cm, whereas the change in distance between ETT tip and carina was 2.02 +/- 0.58 cm. These results suggest that neck extension actually displaces the ETT tip to the vocal cords, increasing the risk of tracheal extubation in older children, although the actual displacement of ETT tip to vocal cords is reduced by tracheal lengthening. IMPLICATIONS: The distance between endotracheal tube tip and vocal cords is directly related to the risk of exubation. Despite tracheal elongation, neck extension actually displaced the endotracheal tube tip to the vocal cords in older children.