Background: Difficulty in weaning from mechanical ventilation occurs in a significant number of intensive care unit patients. While various indices exist, an integrated approach evaluating cardiac and diaphragmatic function may better predict outcomes. Cardiovascular dysfunction during a spontaneous breathing trial is a recognized cause of weaning failure. This study aims to evaluate if the dynamic response of the heart to a preload challenge can predict success.

Objectives: The primary objective is to evaluate the diagnostic accuracy of the percentage change in Left Ventricular Outflow Tract Velocity Time Integral (LVOT VTI) following a Passive Leg Raise (PLR) as a predictor of successful extubation. Secondary objectives include evaluating the predictive value of diaphragmatic thickening fraction and diaphragmatic excursion, and any other independent variable in weaning from mechanical ventilator 

Methods: This is a prospective observational cohort study. Adult patients mechanically ventilated for at least 48 hours who meet standard criteria for a spontaneous breathing trial (SBT) will be included. Before the SBT, baseline LVOT VTI and diaphragmatic ultrasound measurements will be recorded in a semi-recumbent position. A PLR maneuver will be performed to calculate the percentage change in VTI. Patients will then undergo a standardized 120-minute SBT. Weaning success is defined as the absence of re-intubation or the need for non-invasive ventilation for 48 hours post-extubation.

Sample Size and Analysis: A sample size of 60 patients is planned, assuming a 50 percent weaning failure rate to provide 99 percent power to detect significant differences based on previous literature. Diagnostic accuracy will be assessed using Receiver Operating Characteristic (ROC) curves to determine optimal cut-off values. Logistic regression will be used to identify independent predictors of weaning failure.