During weaning from mechanical ventilation, the shift from positive to negative pressure ventilation may be responsible for a cardiac dysfunction that can lead to the development of pulmonary oedema (weaning-induced pulmonary oedema, WIPO) and to the failure of spontaneous breathing trials. The mechanisms leading to WIPO have been described in many studies. The fact that the intrathoracic pressure becomes negative increases right ventricle preload and afterload, reduces right ventricle compliance and increases left ventricle afterload. Arterial hypertension, which results from adrenergic stress and possibly from hypercapnia, usually worsens this latter mechanism. Myocardial ischemia, resulting from the imbalance between the reduction of oxygen delivery (hypoxemia) and increased oxygen demand (unfavourable loading conditions, increase of inotropic and heart rate) may participate in this phenomenon, even though its incidence seems to be low. The means for detecting WIPO in a patient performing a spontaneous breathing trial (SBT) have been widely investigated. To avoid the insertion of a pulmonary artery catheter, which clinicians nowadays tend to avoid when the patient is ready to be extubated, many alternatives methods have been proposed. The increase of left ventricular filling pressure during an SBT was detected with echocardiography, the increase during the test either of B-type natriuretic peptide levels or of extravascular lung water measured by transpulmonary thermodilution can be used. The investigators have also demonstrated that the detection of haemoconcentration during a weaning test, which is related to the filtration of a significant amount of plasma through the alveolar-capillary barrier, allows the detection of WIPO.~Unresolved questions:~The incidence of WIPO is not well defined. In the studies where it has been reported, it ranged between 44% and 87% of SBT failures. However, these studies included a small number of patients and/or included a specific population of patients that had already failed one or more weaning tests. In a monocentric study, the investigators recently reported that WIPO occurred in 59% of cases of SBT failures.~The risk factors for WIPO development are not well defined and have been investigated only by a few studies. In the above-mentioned one, the investigators have identified the presence of pre-existing cardiopathy, pre-existing chronic respiratory failure and obesity as independent risk factors for developing WIPO. However, these results were obtained only from a monocentric cohort.
During weaning from mechanical ventilation, the shift from positive to negative pressure ventilation may be responsible for a cardiac dysfunction that can lead to the development of pulmonary oedema (weaning-induced pulmonary oedema, WIPO) and to the failure of spontaneous breathing trials. However, the incidence and risk factors for WIPO development are not well defined and have been investigated only by a few studies.