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Sternomastoid, Rib Cage, and Expiratory Muscle Activity During Weaning Failure.

We hypothesized that patients who fail weaning from mechanical ventilation recruit their inspiratory rib cage muscles sooner than they recruit their expiratory muscles, and that rib cage muscle recruitment is accompanied by recruitment of sternomastoid muscles. Accordingly, we measured sternomastoid electrical activity and changes in esophageal (DeltaPes) and gastric pressure (DeltaPga) in 11 weaning-failure and 8 weaning-success patients. At the start of trial, failure patients exhibited a higher DeltaPga-to-DeltaPes ratio than did success patients (P = 0.05), whereas expiratory rise in Pga was equivalent in the two groups. Between the start and end of the trial, failure patients developed additional increases in DeltaPga-to-DeltaPes ratio (P < 0.0014) and the expiratory rise in Pga also increased (P < 0.004). At the start of trial, sternomastoid activity was present in 8 of 11 failure patients contrasted with 1 of 8 success patients. Over the course of the trial, sternomastoid activity increased by 53.0 +/- 9.3% in the failure patients (P = 0.0005), whereas it did not change in the success patients. Failure patients recruited their respiratory muscles in a sequential manner. The sequence began with activity of diaphragm and greater-than-normal activity of inspiratory rib cage muscles; recruitment of sternomastoids and rib cage muscles approached near maximum within 4 min of trial commencement; expiratory muscles were recruited slowest of all. In conclusion, not only is activity of the inspiratory rib cage muscles increased during a failed weaning trial, but respiratory centers also recruit sternomastoid and expiratory muscles. Extradiaphragmatic muscle recruitment may be a mechanism for offsetting the effects of increased load on a weak diaphragm.

COMMENTARY

Predicting if a patient will be able to wean from mechanical ventilation is an important part of critical care medicine. Previous observations have been made that the use of inspiratory and expiratory muscles may differ for those who fail weaning compared to those who successfully resume independent breathing. In this study, the authors have demonstrated via EMG analysis that the timing and pattern of ventilatory muscle use may be able to predict failure to wean. Since physical therapists are highly trained to observe and manipulate motor patterns, including those of ventilation, they may be able to give critical input to the health care team regarding ability of a patient to breathe independently. Likewise, interventions aimed at altering dysfunctional motor patterns of ventilation may lead to improvements in ventilator weaning.

Reprinted with permission from Journal of Applied Physiology. 2007;103:140-147. [C] 2007 American Physiologic Society.
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Title Annotation:Commentary on Current Literature
Author:Parthasarathy, S.; Jubran A.; Laghi, F.; Tobin, M.J.
Publication:Cardiopulmonary Physical Therapy Journal
Article Type:Reprint
Geographic Code:1USA
Date:Dec 1, 2007
Words:409
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