The Role of Abdominal Muscle Ultrasound in Mechanically Ventilated Patients

Patients who pass a spontaneous breathing trial with reduced abdominal muscle thickening during cough are at a high risk for liberation failure from mechanical ventilation, according to study results published in the journal CHEST.

The study authors measured abdominal muscle thickness and thickening fraction during cough and expiratory efforts in a 2-part study (ClinicalTrials.gov Identifier: NCT03567564). The first part was a physiologic study conducted in healthy adults and the second part was a prospective observational study conducted in ventilated patients. The healthy adult group was used to determine internal oblique and rectus abdominis thickening fraction with pressure generated during expiratory efforts.

Of the 77 participants in the study, 20 were healthy individuals while 57 were ventilated patients. In the healthy adults, internal oblique and rectus abdominis thickening fraction correlated with pressure generated during expiratory efforts (P <.001). Among the ventilated patients, it was determined that measuring abdominal muscle thickness and thickening fraction was feasible, and that reproducibility was moderately acceptable. During a failed spontaneous breathing trial, thickening fraction of transversus abdominis and internal oblique increased substantially (difference, +13.2%; 95% CI, 0.9%-24.8% and 7.2%; 95%, 2.2%-13.2%, respectively).

Importantly, the combined thickening fraction of transversus abdominis, internal oblique, and rectus abdominis measured during cough was associated with an increased risk of reintubation or reconnection to the ventilator after attempted liberation (odds ratio for failed liberation, 2.1; 95% CI, 1.1-4.4 per 10% decrease in cough in thickening fraction of abdominal muscles).

One important study limitation is that the correlation between expiratory pressure generation and abdominal muscle thickening demonstrated in health adults requires further confirmation in patients undergoing mechanical ventilation.

“Thickening fractions of [transversus abdominis] and [internal oblique] increase during the early course of a failed weaning trial, consistent with elevated expiratory muscle effort,” the study authors wrote. “The measurement of abdominal muscle thickening during cough could be a promising and simple method to identify patients who are at high risk of failed liberation from mechanical ventilation.”

Reference

Schreiber AF, Bertoni M, Coiffard B, et al. Abdominal muscle use during spontaneous breathing and cough in mechanically ventilated patients: a bi-center ultrasound study. CHEST. Published online June 3, 2021. doi:10.1016/j.chest.2021.05.053