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
t he 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 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.
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