ECHOCARDIOGRAPHIC INSIGHTS OF WEANING FAILURE: PREDICTION & PERSPECTIVES

Abstract

It has been reported that around 20-30% of mechanically ventilated patients will develop weaning failure. Since the causes of weaning failure could be diverse, a structured ABCDE approach was developed in order to deal successfully with such patients. Cardiac dysfunction as a reason for weaning failure will be discussed in this article, as well as the role of point of care echocardiography in detection and treatment guidance. Regarding the process of switching patients from positive pressure ventilation to spontaneous breathing, few cardiopulmonary interactions occur with potential of failing especially in patients with cardiac and pulmonary comorbidities. It is well known that in every patient with cardiac dysfunction the level of SvO2 is expected to be lower than 50%. Systolic disfunction is less frequent cause of weaning failure and could be diagnosed by simple measurement of MAPSE or LV FAC. On the contrary, diastolic dysfunction is the leading cause for weaning failure from cardiac origin precipitated by the elevating of preload and afterload by the spontaneous respiration. Diastolic disfunction could be easily assessed by measuring the E/A ratio using transmitral PW Doppler and measuring e’ using septal tissue doppler. Calculation of E/e’ ratio produces a value of Left Atrial Pressure (LAP) which could be converted in Pulmonary Capillary Wedge Pressure (PCWP) by using the equitation of Nageh. Measuring a high E wave, low e’ wave and a higher E/e’ ratio were strongly associated to a diastolic disfunction in a patient that was difficult to wean. Performing echocardiography before and during a spontaneous breathing trial should be a mainstay for ruling out the weaning failure risk because of cardiac dysfunction. Higher values for E/e’ showing high left ventricular filling pressures in patients who are difficult to wean suggest that diastolic dysfunction lies in the essence of weaning failure.