The Evolution of Diaphragm Echodensity During the Early Course of Mechanical Ventilation Differs According to the Eventual Duration of Ventilation
CCCF ePoster library. Riegler S. Oct 4, 2017; 198164; 84
Stephen Riegler
Stephen Riegler
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Abstract
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The Evolution of Diaphragm Echodensity During the Early Course of Mechanical Ventilation Differs According to the Eventual Duration of Ventilation

Riegler, Stephen E 1;  McClelland, William 1;  Lee, Misan 1,2;  Vorona, Stefannie 1;  Dres, Martin 3;  Reid, Darlene 4;  Brochard, Laurent J 5,6;  Ferguson, Niall D 1,5,7,8;  Goligher, Ewan C 1,5.


1Department of Medicine, Division of Respirology, University Health Network, Toronto, Canada;  2Schulich School of Medicine & Dentistry, Western University, London, Canada;  3Respiratory and Critical Care Department, Groupe Hospitalier Pitié Salpêtriére Charles Foix, Assistance Publique Hôpitaux de Paris, Paris, France;  4Department of Physical Therapy, University of Toronto, Toronto, Canada;  5Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, Canada;  6Keenan Centre for Biomedical Research, Li Ka Shing Knowledge Institute, St. Michael’s Hospital, Toronto, Canada;  7Department of Physiology, University of Toronto, Toronto, Canada;  8Institute for Health Policy, Management, and Evaluation, University of Toronto, Toronto, Canada

Introduction
Acute increases in muscle echodensity (sonographic signal attenuation or ‘greyness’) reflect muscle injury in athletes, patients in chronic muscular disease states, and muscle inflammation in critically ill patients. Diaphragm structure and function are known to deteriorate during mechanical ventilation, but changes in diaphragm echodensity have not been described to date.
 
Objectives
We set out to establish the reproducibility of a technique for quantifying diaphragm echodensity in mechanically ventilated patients and to characterize the trajectory of diaphragm echodensity according to clinical outcome and diaphragm function.
 
Methods
Thickness and echodensity of the right hemidiaphragm were measured on a daily basis for up to 14 days of mechanical ventilation. Maximal diaphragm thickening was measured on or before day 7 of ventilation. Echodensity was also measured in 10 healthy subjects. Three different ultrasound devices were employed for the study (Phillips Sparq, Mindray, Fujifilm Sonosite) but the same device and same gain level was employed for all measurements in each subject. Echodensity was quantified using gray scale histogram analysis of the diaphragm region traced out on images (ImageJ, NIH, Bethesda MD). The median grayscale value (range 0-255) was log-transformed to yield a normal distribution of echodensity values. Intra-observer repeatability on multiple images obtained on the same day was assessed in 30 patients. The evolution of diaphragm echodensity over time relative to each patient’s baseline value was compared according to initial change in diaphragm thickness, maximal thickening fraction, and duration of mechanical ventilation.
 
Results
A total of 176 echodensity measurements were obtained in 37 mechanically ventilated patients (mean 3.57, SD 0.61). Intra-observer repeatability for echodensity measurements on sequential images was acceptable (limits of agreement ±0.36, ±12%). Echodensity values varied according to ultrasound gain but not according to ultrasound device or imaging depth. Mean echodensity at baseline in mechanically ventilated patients was not significantly different from healthy subjects (Figure 1, p=0.20); although in 41% of mechanically ventilated patients echodensity exceeded the 95th percentile in healthy subjects (3.8). Baseline echodensity was unrelated to age, sex, severity of illness, organ dysfunction, chronic comorbidity, or sepsis. The early evolution of echodensity differed according to patient outcomes. In patients who required less than 7 days of ventilation, echodensity tended to decrease during the first 4 days of the study, whereas it tended to increase in patients who required more than 7 days (Figure 2A). Similarly, echodensity tended to decrease in patients who exhibited higher maximal thickening fraction after 1 week of ventilation whereas it tended to increase in patients who exhibited impaired maximal thickening fraction (Figure 2B). The evolution of diaphragm echodensity was unrelated to changes in diaphragm thickness over time (Figure 2C) or to variations in SOFA score and sepsis. Echodensity tended to increase over time at increasing inspiratory effort levels (diaphragm thickening > 30%, p=0.02).
 
Conclusions
Diaphragm echodensity can be measured with reasonable precision in mechanically ventilated patients. Increases in echodensity during the early course of ventilation are associated with poor clinical outcomes. Echodensity may be a useful biomarker of diaphragm injury.

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