Which of the following statement(s) is/are true concerning the relationship between cardiac function and effective blood volume?

b. A shift to the right in the Frank-Starling curve is associated with compromised cardiac function

c. Dilutional anemia may contribute to tachycardia even though blood volume and filling pressures are norma

Although physical findings are often adequate to establish a diagnosis and institute management of cardiac failure, direct measurement of filling pressures of the right heart (central venous pressure) or the left heart (pulmonary artery pressure) may be required. Placement of a pulmonary artery catheter allows us to measure cardiac output by thermodilution and, more importantly, to sample mixed venous blood for saturation measurements which tell us the ratio between systemic oxygen delivery and oxygen consumption. From all of these measurements we can determine if cardiac output is normal for the level of filling pressure of the left ventricle, or if contractility is decreased. In the latter case, cardiac output will be lower than predicted for a given level of filling pressure. In the Frank-Starling curve, if the patient is to the right of the normal range, then cardiac function is compromised either because of valvular disease, extrinsic pressure such as pericardial tamponade, or more commonly, a decrease in contractility. If cardiac function and anatomy are normal, then blood volume, filling pressure and cardiac function are related to the Starling curve. The intake and output of fluid and salt is autoregulated to maintain the filling pressure of the left ventricle around 10 mm Hg. Extracellular fluid expansion is usually associated with normal blood volume. Gross expansion of extracelluar space results in deleterious effects if tissue edema can and often do exist with perfectly normal blood volume. In other words, a pulmonary capillary wedge pressure of 5–10 does not rule out fluid overload as a cause of pulmonary or GI dysfunction. In critically ill patients, the fear of hypotension and effect of perfusion usually results in infusion of intravenous salt and water in quantities which exceed losses. Consequently, most patients in the Intensive Care Unit have anemia, dilutional hypoproteinemia, and a compensatory increase in cardiac output. In response to anemia, these patients are tachycardic, even though blood volume is normal, filling pressures are normal, and total body extracellular fluid is excessive.