Impact of change in head and neck position on ultrasound localisation of the cricothyroid membrane: an observational study

Abstract

The ideal position for performing surgical cricothyroidotomy is with full neck extension. Some authors haverecommended marking the cricothyroid membrane before general anaesthesia, typically with the patient’shead and neck in a neutral position. The primary aim of this observational study was to determine whether skinmarks made over the centre of the cricothyroid membrane with the head and neck in the neutral position movedoutside the boundaries of the membrane when the neck was subsequently extended. The secondary aim was toassess changes in the height of the cricothyroid membrane between the neutral and extended positions.Twenty-two volunteers completed the study. With the head and neck in the neutral position, the distancebetween the upper and lower borders (‘height’) of the cricothyroid membrane was measured by a radiologistusing ultrasound. The skin was marked over the mid-point of the membrane. The subject then maximallyextended the neck, and the measurements and marking were repeated. The skin marking over the centre pointof the cricothyroid membrane moved by median (IQR [range]) 5 (4–6[0–10]) mm when the head and neck weremoved from a neutral to a fully extended position. The initial skin mark moved to lie outside the boundary of thecricothyroid membrane in 12 of 22 subjects after extending the neck. The height of the cricothyroid membraneincreased by 30% with the neck extended. We recommend that marking the skin in preparation forcricothyroidotomy should be performed with the neck extended, not with the head and neck in the neutralposition as previously suggested.