Diaphragm echodensity in mechanically ventilated patients: a description of technique and outcomes

Abstract

Background Acute increases in muscle sonographic echodensity reflect muscle injury. Diaphragm echodensity has not been measured in mechanically ventilated patients. We undertook to develop a technique to characterize changes in diaphragm echodensity during mechanical ventilation and to assess whether these changes are correlated with prolonged mechanical ventilation. Methods Diaphragm ultrasound images were prospectively collected in mechanically ventilated patients and in 10 young healthy subjects. Echodensity was quantified based on the right-skewed distribution of grayscale values (50th percentile, ED50; 85th percentile, ED85). Intra- and inter-analyzer measurement reproducibility was determined. Outcomes recorded included duration of ventilation and ICU complications (including reintubation, tracheostomy, prolonged ventilation, or death). Results Echodensity measurements were obtained serially in 34 patients comprising a total of 104 images. Baseline (admission) diaphragm ED85 was increased in mechanically ventilated patients compared to younger healthy subjects (median 56, interquartile range (IQR) 42–84, vs. 39, IQR 36–52, p = 0.04). Patients with an initial increase in median echodensity over time (≥ + 10 in ED50 from baseline) had fewer ventilator-free days to day 60 (n = 13, median 46, IQR 0–52) compared to patients without this increase (n = 21, median 53 days, IQR 49–56, unadjusted p = 0.03). Both decreases and increases in diaphragm thickness during mechanical ventilation were associated with increases in ED50 over time (adjusted p = 0.03, conditional R2 = 0.80) and the association between increase in ED50 and outcomes persisted after adjusting for changes in diaphragm thickness. Conclusions Many patients exhibit increased diaphragm echodensity at the outset of mechanical ventilation. Increases in diaphragm echodensity during the early course of mechanical ventilation are associated with prolonged mechanical ventilation. Both decreases and increases in diaphragm thickness during mechanical ventilation are associated with increased echodensity.

Qualitative and quantitative muscle ultrasound changes in patients with COVID-19–related ARDS

“…On the other hand, it is possible that changes in echodensity may depend on the accumulation fluid resuscitation-related tissue edema [16] . At variance with previous studies [18] , we found that changes in echodensity of both muscles were significantly related to a positive fluid balance. This may reflect the different patient population and the peculiar characteristics of COVID-19 patients, in whom endothelial activation and dysfunction play a key role in the pathogenesis of the disease, by altering the integrity of vessel barrier and potentially favouring fluid extravasation.…”

“…In the current study, muscle mass and quality was assessed using ultrasound; indeed, rectus femoris echodensity, as a marker of muscle quality, increased over the first week by on average 12%, which is similar to prior published data [ 16 , 17 , 31 , 48 , 49 ]. More recently, changes in diaphragm echodensity during the early course of mechanical ventilation were described and associated to a negative outcome [18] . In both cases, the changes increments in muscle echodensity are presumed to be the consequence of either inflammation or infection, or edema due to fluid shifts in the context of volume resuscitation with a positive fluid balance [54] .…”

“…Given the lack of similar investigations in COVID-19 patients, a priori sample size calculation was not performed; the sample size was pragmatically based on a 2-month time frame as well as recently published literature on similar topics [ 17 , 18 ]. Patients with only one ultrasound measurement (i.e.…”

“…In particular, it is well known how both diaphragm and limb muscle size, structure and function deteriorate during the course of ICU stay; sonographic findings of reduced diaphragm thickness and rectus femoris cross-sectional area have been found to be associated with poor clinical outcomes [ 5 , 15 , 16 ]. Similarly, changes in muscle echodensity, easily assessed using grayscale analysis of ultrasound images, have been associated with negative outcomes [ 17 , 18 ].…”

Respiratory and peripheral muscular ultrasound characteristics in ICU COVID 19 ARDS patients

“…Images were saved in JPEG format and echogenicity was quantified using a greyscale histogram analysis of the images. The analysis was performed with ImageJ software ( https://imagej.nih.gov/ij/index.html; NIH, Bethesda, MD, USA), using the square method to define the region of interest for analysis using the histogram function, selecting a free-form area devoid of artefacts [ 25 , 26 ]. Images were reviewed by a second reader (VC) who was not directly involved in imagine acquisition.…”