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 have recommended marking the cricothyroid membrane before general anaesthesia, typically with the patient's head and neck in a neutral position. The primary aim of this observational study was to determine whether skin marks made over the centre of the cricothyroid membrane with the head and neck in the neutral position moved outside the boundaries of the membrane when the neck was subsequently extended. The secondary aim was to assess 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 distance between the upper and lower borders ('height') of the cricothyroid membrane was measured by a radiologist using ultrasound. The skin was marked over the mid-point of the membrane. The subject then maximally extended the neck, and the measurements and marking were repeated. The skin marking over the centre point of the cricothyroid membrane moved by median (IQR [range]) 5 (4-6 [0-10]) mm when the head and neck were moved from a neutral to a fully extended position. The initial skin mark moved to lie outside the boundary of the cricothyroid membrane in 12 of 22 subjects after extending the neck. The height of the cricothyroid membrane increased by 30% with the neck extended. We recommend that marking the skin in preparation for cricothyroidotomy should be performed with the neck extended, not with the head and neck in the neutral position as previously suggested.

Canadian Airway Focus Group updated consensus-based recommendations for management of the difficult airway: part 2. Planning and implementing safe management of the patient with an anticipated difficult airway

“…There is some evidence that full neck extension may increase the height of the CTM by as much as 30%. 111 Pre-induction landmarking of the CTM (e.g., by ultrasound or palpation) should also occur in a position of full neck extension, as the CTM location may change significantly when re-positioning from a neutral to an extended position. 111 …”

Cricothyroidotomy in the emergency setting: indications, techniques and outcomes

“…The mean height of the cricothyroid membrane as measured by two radiologists was 7.89 mm and 7.88 mm in male patients and 6.00 mm and 5.92 mm in female patients. The height of the cricothyroid membrane moreover increases (by up to 20%) when the head and the neck are placed in fully extension [23,29,30], confirming the necessity of performing cricothyroidotomy in this position [30]. It is likely that a decrease in cricothyroid membrane static height as well as in its dynamic height (achieved by extension) may be observed due to calcification associated with the ageing process [28].…”

American Society of Regional Anesthesia and Pain Medicine expert panel recommendations on point-of-care ultrasound education and training for regional anesthesiologists and pain physicians—part I: clinical indications

“…The measurement of the anterior neck has shown that the distance from the skin to the hyoid bone is highly predictive of difficult mask ventilation and intubation. 30 In a patient with a concern for a 'cannot intubate, cannot ventilate' scenario, front of neck airway sonographic identification of the cricothyroid membrane is more accurate than palpation alone [31][32][33][34] and more rapid for emergency airway access. 35 36 Of note, the cricothyroid membrane is highly dependent on neck position; therefore, one must maintain the same position or (following any movement of the neck) rescan to confirm location before attempting an emergency airway.…”

“…41 And finally, it can facilitate nasogastric tube placement. [30][31][32][33][34][35][36][37][38][39][40] Multiple studies have shown the benefit of ultrasound imaging in the correct placement of nasogastric tubes. [42][43][44] See figure 1 for an example of airway ultrasound probe placement, anatomy and sonoanatomy.…”