Diaphragm Ultrasound in the Intensive Care Unit BT - Ultrasound in the Intensive Care Unit

Abstract

Diaphragm dysfunction is an increasingly recognized consequence of critical illness and mechanical ventilation. Ultrasound of the diaphragm is a convenient, noninvasive modality for assessing diaphragm function at the bedside in the intensive care unit and can be used to determine the presence of diaphragm paralysis, dysfunction, and atrophy. Ultrasound can be used to visualize either the dome of the diaphragm or the diaphragm muscle where it abuts the rib cage (zone of apposition of the diaphragm to the rib cage (ZAP)). Either the M- or B-mode can be used to image the diaphragm dome or diaphragm muscle in the ZAP. The motion of the dome during the breathing cycle is best appreciated using the M-mode, whereas the thickening of the diaphragm muscle during inspiration is best appreciated using the B-mode in the ZAP. The advantages of visualizing the diaphragm in the ZAP include measuring the degree to which it contracts during inspiration and its thickness prior to inspiration. These measures have been used to determine whether a diaphragm is paralyzed, if atrophy is present, and suitability of a patient to wean from mechanical ventilation. This chapter will review technical features of imaging the diaphragm dome and the diaphragm in the ZAP and discuss functional correlates of these measures. The capability of ultrasound to specifically evaluate diaphragm function provides the clinician with valuable and immediate information on a traditionally inaccessible organ system which may be used on daily rounds.