Download The Red Cell Volume Procedure - PPT

Non-Imaging In Vivo
Blood Volumes
Red Blood Cells
• Red blood cells are circular, non nuclidic,
biocave discs that are manufactured in the
bone marrow.
• Bone marrow will compensate by making more
RBC’s if there is a loss.
• Normal marrow carries reserves of RBC’s
which can be pushed into circulation when
needed.
• The life span of a RBC is approximately 120
days.
• RBC’s can change size and shape especially in
the sinusoids of the spleen, but then regain
shape.
Red Blood Cells
Abbreviations for Procedures
• Blood Volume Tests (BVT)
• Red Cell Volume/Mass (BCV/M)
• Plasma Volume (PV)
Blood Volume
• Blood volume is kept constant by cardiac
output and atrial pressure decreasing if the
blood volume is decreased.
• This causes kidneys to retain fluid, this
accumulation of fluid brings the blood
volume back to normal.
• The opposite happens if there is a blood
increase causing it to go back to normal.
• However, many drugs and diseases effect
the control of these mechanisms.
• For example, bleeding, the bodies control
mechanisms bring the blood volume back to
normal by increasing plasma volume. But
the red cell volume remains low.
Determining Blood Volume
• Evan’s Blue Dye Method
• The patient is injected with a blue dye and
20 minutes later a blood sample is drawn.
Then you check to see how much blue dye is
in blood. The problem with this is that it is
effected greatly by hemolized and lypholized
samples.
• Dual Tracer Method
• Uses I 125 RISA and Cr 51. To tag RBC’s,
inject both radionuclides at exact same time.
Problem with this test is that it is easily
contaminated and special counting
equipment is needed.
Determining Blood Volume
• Current Method is Red Cell
Volume/Plasma Volume
• Total blood volume can be reliably
estimated by using consecutive
measurement tests of red cell
volume and plasma volume.
Blood Volume Dilution
• By diluting a known activity and
volume of radiotracer in an
unknown volume and then
measuring the activity in a
volume after adequate mixing,
one can determine the unknown
volume.
Theory Formula
• This relationship can be expressed
by the following formula:
• V1C1 = V2C2; therefore V2 = V1 x C1/C2
• Where:
• V1 = volume of tracer injected
• V2 = unknown volume
• C1 = Concentration of injected isotope
(cpm/ml)
• C2 = Concentration of sample obtained
after adequate mixing (cpm/ml)
Indications for BVT
• Evaluation of blood loss and blood
replacement therapy
• Evaluation of extensive trauma and burns
• For preop evaluation of elderly patient
• For evaluation of a patient with anemia
• For evaluation of a patient with possible
polycythemia vera.
• Most common reason for performing a blood
volume study is to differentiate secondary
polycythemia from primary polycythemia vera.
Polycythemia Vera Review
• Polycythemia vera is a condition
characterized by an unusually large
number of red cells in the blood due
to increased production of red blood
cells by the bone marrow.
• Secondary due to disease, cancer, or
change in altitude
• Primary occurs for no known reason, but
thought to be a chromosome disorder
Hematocrit
• Determining blood volume requires that the
technologist perform a hematocrit blood
test on the patient.
• Hematocrit is the percent of packed red cells in
a given sample of blood.
• The test is done by pricking the finger of
the patient and collecting a sample of blood
in a capillary.
• Centrifuge the sample and compare to
chart.
• Normal hematocrit
• Males 40-52%
• Females 36-48%
Hematocrit
• When heparinized blood
(heparin is an anticoagulant)
is centrifuged, the red blood
cells become packed at the
bottom of the tube, while the
plasma is left at the top as a
clear liquid. The ratio of the
volume of packed red cells
to the total blood volume is
called the hematocrit.
Filling Capillary
• One end of a
heparinized capillary
tube is touched to the
drop of blood on the
finger. The tube is filled
to at about 3/4 capacity
by capillary action. Then
the blood-filled end is
sealed with clay, and
placed in a slot in the
microcapillary centrifuge.
Hematocrit Scale Plate
• In order to obtain a value of
hematocrit from the
centrifuged blood sample in
the capillary tube, one must
refer to a scale plate. The
bottom of the packed red cell
column is first lined up with
the "0" line on the scale plate,
and then the scale is moved
under the sample until the top
of the plasma column lines
up with the"100%" line.
Plasmacrit
• 1 - hematocrit = plasmacrit
• Percent of plasma in a given
sample of blood
Procedure for RCV
• Draw 40.5 ml of blood into a a syringe
containing 5 ml of ACD solution.
• Invert syringe 2-3 times.
• Reserve in test tube 5 ml of blood
from syringe to to perform hematocrit.
• Place 5 ml of blood in syringe into a
counting vial and label background.
• Add 100 uCi of Cr51 to ACD vial then
remove vent needle.
RCV Procedure Continued
• Gently mix the blood by intermittent
swirling every 5-10 minutes. Allow
to tag at room temperature for 20
minutes. (22 to 26 degrees C--71.6 to
78.8 degrees F)
• Have patient in recumbent position
for 30 minutes. Blood volume varies
with body position--supine is
standard position.
RCV Procedure Continued
• After 20 minutes, add 50 mg of ascorbic acid to
vial, mix gently and allow to stand for 10 minutes.
• Ascorbic acid reduces the valence state from a
+6 to +3. In +3 state Cr51 cannot penetrate the
red cell membrane and will not tag red cell in
vivo after reinjection).
• Weigh empty syringe that will be used to draw
blood.
• Withdraw exactly 20 ml of tagged solution, weigh
and then reinject intravenously into the patient’s
arm.
• Save the rest of the blood for a standard.
Or Go to: Procedure Outline
RCV Procedure Continued
• After 20 minutes post injection
withdraw 20.5 ml of blood into a
syringe containing 2ml of
heparin from the opposite arm.
• Perform microhematocrit.
• Count each tube, standards,
samples and Bkg
• Calculate RCV
RCV Formula
•V1C1 = V2C2; therefore V2 = V1 x C1/C2
•Where:
–V1 = volume of tracer injected
–V2 = unknown volume
–C1 = Concentration of injected isotope (cpm/ml)
–C2 = Concentration of sample obtained after
adequate mixing (cpm/ml)
RCV and Values
• Blood Volume is usually expressed in ml/kg.
• Volume obtained is divided by patients weight
• Normal findings:
• Males 25 to 35 ml/kg
• Females 20 30 ml/kg
• Example Primary Polycythemia vera results:
• Males
• Greater than 36 ml/kg
• Females
• Greater then 32 ml/kg
Secondary polycythemia = a normal or reduced RBC
Volume
Blood Volumes
• Reportedly the first blood volume
determination was performed during
the French Revolution.
• After guillotine decapitation of a
subject, the blood was drained from the
corpse and measured.
• Today, these measurements are made
in living patients atraumatically.
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