[Ventilation in special situations. Mechanical ventilation in congenital cardiopathies and pulmonary hypertension].

The cardiovascular and respiratory systems act as a functional unit. Mechanical ventilation modifies pulmonary volumes, which generates changes in autonomic nervous system reactivity and provokes tachy- or brady-cardia (depending on the tidal volume used). Mechanical ventilation also decreases cardiac filling volumes (pre-load) and alters pulmonary vascular resistances. In addition, intrathoracic pressures are enlarged, which usually produces a decrease in right atrium filling and an increase in right ventricle afterload. If coronary flow is impaired, myocardial contractility is reduced. However, if cardiac failure is present, mechanical ventilation is especially beneficial because it corrects hypoxia and respiratory acidosis, decreases the work of breathing, and improves stroke volume. Mechanical ventilation in congenital heart diseases is indicated either as lifesaving support or as physiopathological treatment to modify the ratio between pulmonary and systemic flow. As a general rule, if excessive pulmonary blood flow is present, the aim of respiratory support is to increase pulmonary vascular resistance by using high levels of airway pressure and even by delivering FiO2<21%. When there is low pulmonary flow, the lowest possible intrathoracic pressures should be used, especially in cases of pulmonary hypertension, which will also require high FiO2. However, mechanical ventilation has adverse effects and consequently it must be stopped as early as possible, once the child is stable and requires minimal cardiopulmonary support. Weaning can even be performed in the operating room, when the surgical procedure is finished. When this is not possible, weaning should be performed in the pediatric intensive care unit. Because there are no criteria for successful withdrawal of mechanical support in congenital heart disease, general pediatric criteria should be used.