Diaphragm Ultrasound in Critically Ill Patients on Mechanical Ventilation—Evolving Concepts

Abstract

Mechanical ventilation (MV) is a life-saving respiratory support therapy, but MV can lead to diaphragm muscle injury (myotrauma) and induce diaphragmatic dysfunction (DD). DD is relevant because it is highly prevalent and associated with significant adverse outcomes, including prolonged ventilation, weaning failures, and mortality. The main mechanisms involved in the occurrence of myotrauma are associated with inadequate MV support in adapting to the patient’s respiratory effort (over- and under-assistance) and as a result of patient-ventilator asynchrony (PVA). The recognition of these mechanisms associated with myotrauma forced the development of myotrauma prevention strategies (MV with diaphragm protection), mainly based on titration of appropriate levels of inspiratory effort (to avoid over- and under-assistance) and to avoid PVA. Protecting the diaphragm during MV therefore requires the use of tools to monitor diaphragmatic effort and detect PVA. Diaphragm ultrasound is a non-invasive technique that can be used to monitor diaphragm function, to assess PVA, and potentially help to define diaphragmatic effort with protective ventilation. This review aims to provide clinicians with an overview of the relevance of DD and the main mechanisms underlying myotrauma, as well as the most current strategies aimed at minimizing the occurrence of myotrauma with special emphasis on the role of ultrasound in monitoring diaphragm function.

The Role of Ultrasonography in the Process of Weaning from Mechanical Ventilation in Critically Ill Patients

“…This condition, referred to as ventilator-induced diaphragmatic dysfunction (VIDD), may affect the ability of the patient to discontinue MV [25]. VIDD may occur shortly after the initiation of ventilation and worsen over time, depending on the mode of ventilation used and other associated risk factors [26]. As a result, it is important to assess diaphragmatic function to predict the patient's ability to wean from MV and sustain spontaneous breathing.…”

“…The fibrous layer located in the center of the diaphragm is often identified by a third hyperechoic line that can be observed within the non-echogenic layer [35]. Tdi is measured at the end of expiration (Tdi-exp) and inspiration (Tdi-insp) as the distance between the diaphragmatic pleura and the peritoneum using the B-mode or M-mode [26].…”

“…During inspiration, the diaphragm moves downwards towards the probe. If there is absent or reduced movement that falls below normal reference values or movement that goes against the probe, it indicates dysfunction of the diaphragm [26]. The success rate for visualizing E during tidal breathing (>95%) is high, while during maximal breathing visualization is more difficult, especially on the left side [44].…”

“…During the weaning process, clinicians use objective clinical criteria and sometimes physiological tests like diaphragmatic ultrasonography to predict whether a patient is likely to tolerate weaning in a process called readiness testing. When considering the predictive role of diaphragmatic ultrasonography in assessing the preparedness for weaning from MV, findings are conflicting [26]. Numerous studies suggested that diaphragmatic excursion cut-off values of 10 mm to 13 mm or more [49][50][51][52] and diaphragmatic thickening fraction values of 20 to 30% or more are predictable for successful extubation [52][53][54].…”

“…STUS software works by tracking a group of speckles throughout the contractile cycle and measuring their displacement and deformation in relation to each other. The extent of deformation is referred to as 'strain,' while "strain rate" quantifies the deformation velocity [26,32]. A recent study by Oppersma et al has shown a strong correlation between strain, strain rate, and transdiaphragmatic pressure in healthy individuals [68].…”