The Validity of Thorathic Fluid Content as Non Invasive Predictor on Weaning of Mechanical Ventilation in Critically Ill Patients

Introduction Weaning from mechanical ventilation (MV) could be described as the process of removing ventilator support. Weaning from MV often implies two separate but closely linked views of care, elimination of MV of any artificial airway. Weaning from mechanical ventilation is a challenging step during recovery from critical illness (1).

Earlier patient weaning from mechanical ventilation is recommended to avoid complications of prolonged mechanical ventilation; however, premature weaning might result in extubation failure which is associated with poor outcomes (2).

The first step in weaning process is screening patients for readiness to be weaned from mechanical ventilation followed by the spontaneous breathing trial (SBT) by checking various indices carefully before starting SBT to ensure adequate oxygenation, ventilation, and airway reflexes (3).

However, a percent of patients fail and are re-intubated despite fulfillment of all the current weaning criteria and this may be due to the heterogeneity of critically ill patients which impairs the predictive accuracy of the available indices in different patient subgroups (4).

Various measures had been previously reported for evaluation of volume status such as fluid balance and echocardiography before the SBT aiming to identify patients who would benefit from diuretic therapy to achieve successful weaning from mechanical ventilation (5).

Nowadays, there is an increasing interest in cardiac factors, such as lung congestion and hypervolemia, as contributing elements in weaning failure and that needs expert physician such as echocardiography (6). So thoracic fluid content measurement may also be beneficial, more accurate and could give us a good idea about weaning of patients from mechanical ventilation (7).

Thoracic fluid content represents the whole (extravascular, intravascular, and intrapleural) fluid component in the thorax; thus, TFC was considered to provide an estimation of the extravascular lung water in absence of significant pleural or pericardial effusion (8,9).

Trans-thoracic echocardiography is a non-invasive tool that delivers bedside cardiac function evaluation. Echocardiography is now widely used to evaluate cardiac function during the ventilator weaning process. Impaired left ventricular systolic and diastolic function were reported to be good predictors of weaning failure (10).

Inferior vena cava (IVC) size and collapsibility can give us an idea about hypovolemic patients for estimation of right atrial pressure. Inferior vena cava diameter can be measured using the trans-thoracic echo-cardio graphic subcostal window in the sagittal plane. M-mode imaging allows high-frame rate measurements of size changes throughout the respiratory cycle (11).

Trans-mitral to mitral annular early diastolic velocity ratio (E/Ea ratio) is an echo Doppler non invasive estimation of left ventricular filling pressures and can be measured using trans-thoracic echo-cardiograph in the apical four-chamber view then pulse-wave Doppler imaging is done to record trans-mitral and mitral annular flow in early diastole (12).