Diaphragm Echogenicity in Mechanically Ventilated Patients: Measurement Precision and Preliminary Findings
CCCF ePoster library. Riegler S. Oct 31, 2016; 150888; 10
Stephen Riegler
Stephen Riegler
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Topic: Basic or Translational Science

Diaphragm Echogenicity in Mechanically Ventilated Patients: Measurement Precision and Preliminary Findings


Stephen E. Riegler1,2; Misan Lee1,3; Stefannie Voronna1; Martin Dres4,5; Luciana Vieria7; Darlene Reid6; Laurent J. Brochard4,5; Niall D. Ferguson1,4; Ewan C. Goligher1,4

1
​Department of Medicine, Division of Respirology, Sinai Health System and the University Health Network, Toronto, Canada;  2Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada;  3Schulich School of Medicine & Dentistry, Western University, London, Canada;   4Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, Canada;  5Keenan Centre for Biomedical Research, Li Ka Shing Knowledge Institute, St. Michael’s Hospital, Toronto, Canada;  6Department of Physical Therapy, University of Toronto, Toronto, Canada;  7Health Sciences and Technologies PhD Program, University of Brasilia, DF, Brazil




 

Abstract:

Introduction
Mechanical ventilation is associated with deleterious changes in diaphragm structure and function. Changes in muscle structure can be detected using ultrasound by measuring muscle thickness and echogenicity. Increased muscle echogenicity has been shown to reflect inflammation in the axial skeletal muscles of critically ill patients. It is unknown whether diaphragm echogenicity changes significantly during ventilation.

Objectives
We set out to develop a technique for quantifying diaphragm echogenicity, to confirm the reproducibility of this technique, and to employ this technique to assess the variation in echogenicity over time during mechanical ventilation.

Methods
The right hemidiaphragm was imaged in cross-section in the zone of apposition on a daily basis for the first 14 days of ventilation. Several different ultrasound devices were employed (but the same device was employed for each subject). Images were saved in JPEG format and echogenicity was quantified using a gray scale histogram analysis of the images.  The analysis was performed with ImageJ software, using the trace method – selecting a free-form area devoid of artefacts between (but excluding) the pleural and peritoneal lines on the image of the diaphragm. The median grayscale value (range 0-255) was log-transformed to yield a normal distribution of echogenicity values. Thirty images were randomly selected for measurement in duplicate to quantify intraobserver and interobserver measurement reproducibility. We assessed the pattern of changes in diaphragm thickness over time during mechanical ventilation. The effect of inspiratory effort (measured by diaphragm thickening fraction) on echogenicity was evaluated using linear mixed effects regression.

Results
A total of 136 echogenicity measurements were obtained in 27 mechanically ventilated patients. Measurement reproducibility both within and between observers was excellent (limits of agreement < 10% of mean echogenicity measurement) (Figure 1, Table 1). Echogenicity measurements tended to be lower when obtained using the Phillips Sparq compared to either the Sonosite or Mindray devices (p=0.06 for difference between units). Echogenicity measurements were unaffected by depth (p=0.72) or frequency (p=0.08). Diaphragm echogenicity varied considerably in many patients over the early course of ventilation (Figure 2). Changes in echogenicity did not correlate with changes in diaphragm thickness (p=0.29). Diaphragm thickening fraction values above 30% were associated with a significant increase in echogenicity over time (15%/day, 95% CI 5-23%) compared to diaphragm thickening fraction below 30% (-1%/day, 95% CI -3%-2%) (p=0.008 for interaction).

Conclusion
Diaphragm echogenicity can be measured with precision in mechanically ventilated patients. Echogenicity varies considerably over time and may reflect changes in muscle structure independent of the development of atrophy. High levels of inspiratory effort are associated with significant increases in echogenicity. These findings raise the possibility that excess inspiratory effort under partially assisted ventilation could lead to diaphragm injury and inflammation. Further work is required to determine the normal range of echogenicity and its normal variation over time in healthy subjects.
 


References:

Goligher, E. C., Fan, E., Herridge, M. S., Murray, A., Vorona, S., Brace, D., … & Ferguson, N. D. (2015). Evolution of Diaphragm Thickness during Mechanical Ventilation: Impact of Inspiratory Effort. American Journal of Respiratory and Critical Care Medicine, 192(9), 1080-1088.

Puthucheary, Z. A., Phadke, R., Rawal, J., McPhail, M. J. W., Sidhu, P. S., Rowlerson, A., … & Montgomery, H. E. (2015). Qualitative Ultrasound in Acute Critical Illness Muscle  Wasting. Critical Care Medicine, 43(8), 1603-1611.

Sarwal, A., Parry, S. M., Berry, M. J., Hsu, F-C., Lewis, M. T., Justus, N. W., … & Cartwright,  M. S. (2015). Interobserver Reliability of Quantitative Muscle Sonographic Analysis in the Critically Ill Population. Journal of Ultrasound Medicine, 34, 1191-1200.
 



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