A narrative review of diaphragm ultrasound to predict weaning from mechanical ventilation: where are we and where are we heading?

Abstract

Background: The use of ultrasound to visualize the diaphragm is well established. Over the last 15 years, certain indices of diaphragm function, namely diaphragm thickness, thickening fraction and excursion have been established for mechanically ventilated patients to track changes in diaphragm size and function over time, to assess and diagnose diaphragmatic dysfunction, and to evaluate if these indices can predict successful liberation from mechanical ventilation. In the last 2 years, three meta-analyses and a systematic review have assessed the usability of diaphragmatic ultrasound to predict successful weaning. Since then, further data have been published on the topic.

Conclusions: The aim of this narrative review is to briefly describe the common methods of diaphragmatic function assessment using ultrasound techniques, before summarizing the major points raised by the recent reviews. A narrative summary of the most recent data will be presented, before concluding with a brief discussion of future research directions in this field.

Keywords: Diaphragm; Diaphragm ultrasound; Muscle atrophy; Thickening fraction.

Fig. 1

Subcostal view of the diaphragm (b) in B-mode at end inspiration (1) and at expiration (2) seen below the liver (a)

Fig. 2

Diaphragm excursion as assessed via M-mode ultrasonography, where a is the diaphragm, b is at the end of a deep inspiratory effort, c is at end expiration and d is the liver

Fig. 3

M-mode ultrasonography demonstrating three tidal inspiratory efforts (a) and a deep inspiratory effort (b)

Fig. 4

Diaphragm thickness in B-mode thoracic view at end expiration (1) and inspiration (2) in a heathy volunteer. The diaphragm can be seen between two echogenic layers (a) with the intercostal compartment above (b). The two muscle layers sit between two ribs (c)