Managing low cardiac output states: maintaining volume after cardiac surgery.

Low cardiac output after cardiac surgery may be caused by hypovolemia, myocardial depression, vasoconstriction, and dysrhythmias. Postoperative hypovolemia occurs because of blood volume loss and decreased diastolic filling. Diuresis, intravascular fluid shift into the interstitium, hormonal influences, and bleeding deplete blood volume. Diastolic filling may be compromised by positive end-expiratory pressure, vasodilation, dysrhythmias, and venous return obstruction. The primary indicator of intravascular volume is ventricular preload, which may be measured indirectly with central venous pressure, left atrial pressure, or pulmonary capillary wedge pressure. Recognition of hypovolemia is aided through the use of cardiac pressure trend monitoring and evaluation of noninvasive indicators of hypovolemia. Nursing goals, in response to hypovolemia, are to increase the circulating volume, optimize oxygen delivery, stabilize hemodynamics, improve tissue perfusion, and prevent shock.