Abdominal muscle thickening tied to weaning outcomes in mechanically ventilated patients

Mechanically ventilated patients use their abdominal muscles during spontaneous breathing and when coughing, and a recent study shows that the thickening of such muscles on ultrasound is associated with the airway pressure generated by expiratory efforts.

Accordingly, patients with reduced abdominal muscle thickness during cough are likely to be kept on mechanical ventilation.

The study was conducted in two parts: the first part was a physiological study involving 20 healthy individuals, while the second was a prospective observational study in 57 mechanically ventilated patients. Abdominal muscle thickness and thickening fraction (TF) were measured during cough and expiratory efforts in both cohorts.

Healthy individuals exhibited thickening of internal oblique and rectus abdominis, with the thickening fraction associated with pressure generated during expiratory efforts (p<0.001).

In the second part, abdominal muscle thickness and thickening fraction were measured in all mechanically ventilated patients with a moderately acceptable reproducibility. During a failed spontaneous breathing trial (SBT), there was a substantial increase seen in thickening fraction of transversus abdominis (13.2 percent, 95 percent confidence interval [CI] 0.9–24.8) and internal oblique (7.2 percent, 95 percent CI 2.2–13.2).

Each 10-percent decrease in the combined thickening fraction of transversus abdominis, internal oblique, and rectus abdominis measured during cough correlated with a twofold higher likelihood of reintubation or reconnection to the ventilator after attempted liberation (odds ratio 2.1, 95 percent CI 1.1–4.4).

The findings suggest that measuring abdominal muscle thickening on ultrasound in mechanically ventilated patients provide clinically relevant information about abdominal muscle function and liberation outcomes.