Theoretical optimal cricothyroidotomy incision length in female subjects, following identification of the cricothyroid membrane by digital palpation.

BACKGROUND: Misidentification of the cricothyroid membrane is frequent in females, placing them at risk of difficult or failed cricothyroidotomy in the event of failed oxygenation. If anatomy is impalpable, the current guidelines of the Difficult Airway Society, based on expert opinion, recommend an 8-10 cm vertical incision to facilitate access to the cricothyroid membrane. At present no evidence-based guideline exists regarding optimum site or length. We investigated the likelihood of inclusion of the cricothyroid membrane, within hypothetical vertical midline incisions, in a female population.

METHODS: We asked clinicians to identify the cricothyroid membrane in both the neutral and extended head positions using palpation, the point identified acting as the theoretical midpoint of a cricothyroidotomy incision. We then identified the cricothyroid membrane using ultrasound. We determined the minimum incision length that would be required to ensure that the cricothyroid membrane lay within its boundaries, if clinician digital palpation was the method of cricothyroid membrane localisation.

RESULTS: Ninety female subjects were recruited. Theoretical incisions of 7 and 8 cm were required for successful cricothyroidotomy in the neutral and extended head positions respectively. This was necessary because of the high failure rate of cricothyroid membrane identification (80.9%) and the wide range of error (7.2 cm in a vertical plane).

CONCLUSIONS: Based on clinical estimation of the location of the cricothyroid membrane, an incision length of 8 cm, using the clinician's best estimate as its midpoint, would overlie all cricothyroid membrane locations. Our data support the current Difficult Airway Society guidelines for cricothyroidotomy incision length.