Cardiac Load

Cardiac dysfunction is among the most common barriers to weaning [82].

The onset of ARDS respiratory failure may be precipitated by, exacerbate or importantly mask, congestive and right heart failure. Positive pressure reduces pulmonary edema, provides increased alveolar pressures, and reduces afterload. With weaning, spontaneous breathing is reestablished; the process reverses with a negative pleural pressure during inspiration [83]. This decrease in intrathoracic pressure increases the systemic venous return pressure gradient, the right ventricular (RV) preload, the central blood volume, and subsequently the LV preload [84]. A second effect is a decrease of the LV ejection pressure gradient, increasing the LV afterload [85]. As a consequence, respiratory and cardiac failure may occur, associated with increased work of breathing and hypoxemia.

Diagnosis and monitoring, augmented by echocardiography, allow titration of treatment by diuretics, vasodilators, inotropes, and coronary angioplasty when indicated. Using diuretics guided by brain natriuretic peptide (BNP) measurements shortens weaning suggesting that negative fluid balance using diuretics could hasten extubation [16]. The use of a conservative fluid strategy shortened MV in patients with acute lung injury although poor longer-term cognitive outcomes are concerning [66, 86].