Measurement of urine output, mean arterial pressure (MAP), heart rate (HR), pulmonary wedge (PWP), and cardiac index (CI) reflects the status of the central blood volume which include the heart, brains, and lungs. Such measurements do not reflect the status of the peripheral blood volume….nor do the measurements give an indication of the status of the total blood volume. The volume of blood lost during acute blood loss cannot be accurately estimated from measurements of peripheral venous hemoglobin concentration and hematocrit value.
C. Robert Valeri, MD, Physiology of Blood Transfusion, Chapter 22, “Surgical Intensive Care,” Little Brown and Company, Boston, MA, 1993.
Blood volume measurements have been available for almost 60 years. The test often required 4 to 8 hours to perform and was very difficult to perform accurately. Because of this, blood volume measurements were rarely obtained.
In situations in which knowledge of the circulating blood volume is indicated, a number of proxy tests are commonly performed. These include hematocrit or hemoglobin tests, which only measure the ratio of red cells to plasma. Pulmonary artery catheterization may be used to help guide fluid and cardiovascular management decisions, but the method is invasive and does not specifically reflect circulating blood volume. Hemodynamic variables, such as arterial pressure, cardiac index, and pulmonary wedge pressure provide information about cardiovascular circulation and perfusion but do not differentiate between the effects of total volume versus vasomotor tone or response.
The BVA-100 provides a direct accurate measurement of the circulating blood volume in approximately 1.5 hours. The procedure has been found to be viable in a clinical setting. In addition, the instruments software calculates a normal blood volume for each patient based on that patients height and weight, and compares the measured blood volume to the patients norm. This can provide invaluable information that cannot be otherwise obtained and can be useful in fluid and cardiovascular management decisions, as well as in the diagnosis of many hemodynamic and cardiovascular disorders.