Heart-related weaning issues

Abstract

Acute pulmonary oedema is a frequent cause of failure of weaning from mechanical ventilation, especially in patients with underlying left-sided heart disease and associated chronic obstructive pulmonary disease. There are three main factors that can lead to the development of cardiogenic pulmonary oedema during weaning: (1) negative intrathoracic pressure, which leads to an increase in systemic venous return pressure, central blood volume and left ventricular preload, as well as increasing the left ventricular afterload; (2) increase in respiratory rate, leading to an increase in myocardial oxygen demand, which increases the risk of myocardial ischaemia in predisposed patients and (3) intense stimulation of the sympathetic nervous system caused by emotional stress, hypoxaemia, and in some cases, hypercapnia when patients are disconnected from a ventilator. An increase in pulmonary artery occlusion pressure measured during a spontaneous breathing trial using a pulmonary artery catheter can be used to help diagnose weaning-induced pulmonary oedema. Less invasive diagnostic methods have also recently been developed. Thus, during a spontaneous breathing trial, changes in echocardiographic indices of left ventricular function or in B-type natriuretic peptide (BNP) biomarker levels and in plasma protein concentration have been reported to have diagnostic value in weaning-induced pulmonary oedema. It is important to diagnose patients presenting with weaning-induced pulmonary oedema, as appropriate treatment with diuretics and/or vasodilators (e.g. nitrate derivatives), based on the predominant mechanism, can enable successful weaning.