Mechanical ventilation is an essential, life-saving therapy in the ICU, allowing critically ill patients to rest and recover. Transitioning patients back to spontaneous breathing-known as weaning-is clinically challenging. The first attempt, the Spontaneous Breathing Trial (SBT), fails in 10-30% of cases. Identifying the mechanisms behind failure is crucial, as unsuccessful weaning prolongs ICU stay and increases the risk of reintubation, which worsens prognosis. The SCOUT study aims to improve prediction and management of weaning failure.
The main objective of the study is to evaluate whether a specific ultrasound-based method, the Venous Excess Ultrasound Score (VExUS), can predict failure of weaning from mechanical ventilation. A key pathophysiological factor is systemic venous congestion. When a patient initiates an SBT, the increased respiratory effort shifts venous return and may precipitate cardiovascular decompensation with pulmonary fluid accumulation, termed weaning-induced pulmonary edema (WIPO). Notably, this may occur even in patients without known cardiac disease.
Detecting clinically relevant congestion before SBT is difficult. Fluid balance and body weight are imprecise, physical examination lacks sensitivity, and biomarkers such as NT-proBNP have limited predictive capacity. VExUS offers a promising, non-invasive approach by directly assessing venous flow patterns in major veins (inferior vena cava, hepatic, portal, and renal veins), providing an estimation of systemic venous pressure and congestion. The central hypothesis is that elevated VExUS grades prior to SBT will identify patients at high risk of failure, enabling proactive optimization and potentially improving outcomes.
SCOUT is designed as a prospective, multicenter, observational study. Standard clinical management of mechanical ventilation and weaning remains unchanged. After informed consent, baseline data will be obtained immediately before SBT, including vital signs, ventilator parameters, blood sampling, and three non-invasive ultrasound assessments: cardiac, pulmonary, and VExUS. During the 30-120-minute SBT, the patient breathes with reduced ventilatory support while their clinical tolerance is evaluated. At the end of the SBT, selected measurements are repeated. Weaning failure is defined as: early termination of SBT due to intolerance, need for invasive or non-invasive ventilation within 48 h after extubation, or death within 48 h. Data are anonymized and stored securely (REDCap) in compliance with Spanish and EU data protection regulations.
The study is low-risk and provides no direct individual benefit, but may benefit future ICU patients by improving weaning strategies and prognostication.
Patients aged > 18 years.
Admitted to an Intensive Care Unit (ICU).
Requiring invasive mechanical ventilation for more than 48 hours.
Meeting the center's standard criteria to begin weaning and undergo an SBT.
Inadequate ultrasound window for assessment.
Presence of "do not reintubate" orders.
Patients with a tracheostomy.
Presence of atrial fibrillation.
Single group
point of care ultrasound
Diagnostic testComplete set of pulmonary, cardiac, and VExUS ultrasounds
Weaning failure
The primary objective of the SCOUT study is: To evaluate the utility of VExUS to predict weaning failure from mechanical ventilation. Defining the Weaning Failure A patient is considered to have met the primary outcome if they experience any one of the following events: * The Spontaneous Breathing Trial (SBT) is interrupted due to clinical intolerance, requiring reconnexion to mechanical ventilation. * The patient is extubated but requires rescue with mechanical ventilation (either invasive or non-invasive) within the subsequent 48 hours. * The patient is extubated and dies within the subsequent 48 hours.
Utility of the VExUS score for predicting the failure of weaning from mechanical ventilation
The primary objective of the SCOUT study is: To evaluate the utility of VExUS to predict weaning failure from mechanical ventilation. The Venous Excess Ultrasound Score (VExUS) is expressed as four grades (0-3): VExUS 0: No congestion VExUS 1: Mild congestion VExUS 2: Moderate congestion VExUS 3: Severe congestion A patient is considered to have met the primary outcome (weaning failure) if they experience any one of the following events: * The Spontaneous Breathing Trial (SBT) is interrupted due to clinical intolerance, requiring reconnexion to mechanical ventilation. * The patient is extubated but requires rescue with mechanical ventilation (either invasive or non-invasive) within the subsequent 48 hours. * The patient is extubated and dies within the subsequent 48 hours.
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