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■ Preload ■ Afterload ■ Oxygen demand ■ Cardiopulmonary interactions Therapeutic Tools A variety of tools are available for the treatment of acute circulatory failure in children The remainder of this chapter addresses how these essential hemodynamic tools can be applied to infants and children with acute circulatory failure in the ICU Ventilation In addition to its primary function, which is to maintain gas exchange, ventilation is an important hemodynamic tool in children with cardiac disease, and can be used to optimize the systemic perfusion Cardiopulmonary interactions describe the interplay between spontaneous or mechanical ventilation and the cardiovascular system These interactions differ greatly in health and disease In addition, unique interactions are present in children with cardiac disease The application of mechanical ventilation in children with acute circulatory failure requires an understanding of the underlying diagnosis, physiology, and how cardiopulmonary interactions may be tailored for an individual Cardiopulmonary Interactions in the Healthy Circulation In the healthy circulation, the fall in intrathoracic pressure during spontaneous inspiration is associated with an increase in cardiac output secondary to increased right ventricular (RV) preload Conversely, positive pressure ventilation produced a reduction in venous return and right heart filling, resulting in a small reduction in cardiac output that was proportional to the mean airway pressure (Fig 64.1).20 FIG 64.1 Influence of airway pressure on the cardiac output of healthy individuals The reduction in cardiac output during positive pressure ventilation is due to the effects of airway pressure on right cardiac filling The change in cardiac output is related to airway pressure, such that a higher mean airway pressure and longer inspiratory time (A and B) produces a significant fall in cardiac output (C) A low airway pressure, with a short inspiratory time, does not adversely affect cardiac output The effects of ventilation are not confined to the preload of the right heart Positive pressure ventilation can also impede the emptying of the right heart through its effects on pulmonary vascular resistance and may also reduce left ventricular (LV) afterload through a reduction in transmural LV pressure.21 Although these hemodynamic effects are of minimal importance in the healthy individual, in the presence of circulatory instability, cardiopulmonary interactions become much more relevant in both the development of the problem and in its treatment Cardiopulmonary Interactions in Children With Systolic Ventricular Dysfunction Positive pressure ventilation decreases work of breathing and RV filling and reduces LV afterload These cardiopulmonary interactions can be beneficial in
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