Integrated Multimodal Critical Care Ultrasound for Mechanism-Based Prediction of Weaning Failure: A Prospective Pilot Study

Background: Weaning from mechanical ventilation remains a complex and failure-prone process, with extubation failure rates reaching up to 30%. Conventional indices inadequately capture the multifactorial physiology underlying weaning failure. This study aimed to evaluate whether a multimodal ultrasound approach could improve the identification of mechanisms and prediction of extubation outcomes. Methods: In this prospective pilot observational study, adult mechanically ventilated patients with preserved left ventricular ejection fraction (LVEF ≥ 50%) undergoing spontaneous breathing trials (SBT) were included. Multimodal ultrasound assessment—including transthoracic echocardiography (TTE), lung ultrasound (LUS), diaphragmatic ultrasound (DUS), and venous excess ultrasound (VExUS)—was performed at two predefined time points. Conventional respiratory mechanics parameters were recorded concurrently. The primary outcome was a composite of SBT failure (permanent weaning failure) or reintubation within 48 h. Results: A total of 27 patients were included, of whom 8 (29.6%) experienced extubation failure (5 permanent SBT failure, 3 post-extubation reintubation). Respiratory system compliance showed consistent associations with extubation failure across both ROC and regression analyses (AUC 0.806, 95% CI 0.611–1.000; cutoff ≤ 45 mL/cmH2O; sensitivity 88%; specificity 74%; NPV 93%). Diaphragm excursion was significantly lower in the failure group (p = 0.042) and showed useful predictive performance (AUC 0.750, 95% CI 0.565–0.935; cutoff ≤ 24 mm; sensitivity 100%; specificity 58%; NPV 100%). Lung ultrasound, VExUS, and echocardiographic parameters did not demonstrate significant predictive value. Given the limited number of outcome events (n = 8) and events-per-variable ratio of 4.0 (EPV = 4.0), all multivariable findings are hypothesis-generating. Conclusions: In this prospective pilot study, respiratory system compliance and diaphragm excursion were associated with extubation failure in patients with preserved left ventricular function, while echocardiographic indices, LUS, and VExUS grading did not demonstrate significant predictive value. These hypothesis-generating findings suggest that impaired diaphragmatic function and reduced compliance may be more closely associated with weaning failure than cardiopulmonary congestion parameters. However, given the small sample size, low EPV, and single-centre design, all findings require validation in larger multicentre studies including patients with impaired systolic function.