The challenges of using ultrasound to measure the trachea: a brief report.

BACKGROUND

Tracheostomy is a common procedure in intensive care medicine, involving the insertion of an artificial airway through the front of the neck into the trachea. The size of tracheostomy tube in relation to the trachea is important, influencing clinical outcomes and patient experience. Ultrasound is readily available at the bedside and airway applications have been reported, including airway measurement. However, the presence of air within airway lumina presents challenges to ultrasound and causes artefact. Guidance is lacking on tracheal sonography and measurement.

AIM: to characterize the sonoanatomy of the inner tracheal wall and determine reference points for measuring tracheal diameter.

METHODS

exploratory study; pig, sheep and human tracheas were flooded to eliminate air artefact. Still and video images of flooded and dry specimens were compared to help differentiate air artefact from anatomical landmarks; locate the inner tracheal wall; and determine reference points for measurement.

RESULTS

The inner tracheal wall presented as a bright line anteriorly but was not visible where cartilages were calcified or laterally. Mirror images of the tracheal wall and peri-tracheal structures were seen within the air column. A method of measuring the trachea was developed based on the outer border of the trachea and its reflection.

CONCLUSION

Tracheal rings can be identified by distinctive sonographic features. Inner tracheal width may be estimated by averaging the diameters of the outer-tracheal border and its reflection within the air column. Further clinical studies of relevant patient populations are needed to determine accuracy and reliability of estimates.