Association between abdominal muscle weakness and weaning failure in mechanically ventilated critically ill patients: an ultrasound assessment

Background: Ultrasound evaluation of abdominal muscle activity during cough may provide a practical tool to identify patients at risk of failure of liberation from mechanical ventilation (MV). We aimed to investigate the association between abdominal muscle weakness (AMW), assessed by ultrasound during coughing, and failure of liberation from MV within 48 h after the first liberation attempt, with liberation failure within 7 days as a secondary outcome. We also explored its relationship with diaphragm dysfunction (DD) and ICU-acquired weakness (ICUAW). Methods: We conducted a prospective cohort study including intubated or tracheostomized critically ill patients at high risk of failure of liberation from MV, who had been ventilated for at least 48 h, and had successfully completed a spontaneous breathing trial (SBT). Before the liberation attempt, all patients were assessed for AMW, defined as the overall thickening fraction of the abdominal muscles during cough (TFabs) measured by ultrasound. DD was assessed using ultrasound and defined by a diaphragm thickening fraction (TFdi) below 29%, while ICUAW was evaluated using the Medical Research Council scale or the simplified peripheral nerve test in uncooperative patients. Results: A total of 46 patients were included in the study. Nine (20.5%) patients had AMW, ICUAW, and DD simultaneously, whereas 10 (22.9%) had isolated AMW. AMW was not associated with ICUAW (p = 0.28) or DD (p = 0.97). Liberation from MV within 48 h was successful in 30 patients (65.2%) and failed in 16 (34.7%). During the 7-day follow-up, liberation failure occurred in 3 of the 30 patients (10.0%) who remained free from MV within 48 h. Multivariable logistic regression analysis showed a higher probability of liberation failure within 48 h (OR 9.4, CI 1.1–75.2, p = 0.03) and 7 days (OR 14.8, CI 1.6–136.1, p = 0.02) in patients with AMW. ICUAW was associated with liberation failure within 48 h (OR 8.5, CI 1.5–46.8, p = 0.01) and 7 days (OR 20.4, CI 2.7–155.0, p < 0.01), whereas the presence of DD was not related to either outcome. Conclusions: Ultrasound evaluation of abdominal muscle function during cough, together with an assessment of ICUAW, may help identify critically ill patients at risk of failure of liberation from MV and may support clinical assessment of readiness for liberation.