Intrathoracic Blood Volume Accurately Reflects Circulating Volume Status in Critically Ill Patients

In general, central venous pressure (CVP) and pulmonary capillary wedge pressure (PCWP) are used for control and management of circulating blood volume. It has been demonstrated that there is a good correlation between left atrial pressure and PCWP during spontaneous breathing and intermittent positive pressure ventilation [1, 2, 7]. However, the introduction of continuous pressure ventilation (CPPV) has complicated the use of, e.g., PCWP as the indicator of left ventricle (LV) preload greatly; more than 10 years ago it was shown that PCWP poorly reflects circulating volume status during CPPV in subjects with normal lungs [13, 16]. In an investigation by Shippy et al. [12] of over 1500 occasions of clinical indication or suspicion of either hypovolemia or hypervolemia during periods of critical illness in patients admitted to the surgical ICU or during early resuscitation from hypotensive shock with administration of a fluid load, blood volume and values of the commonly monitored variables, including CVP, PCWP, and cardiac output (CO.), improved appropriately. However, the correlation coefficients, in general, were not good. The authors concluded that the commonly monitored variables in and of themselves do not reflect adequately the blood volume status in critically ill patients.