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: V 1 C 1 = V 2 C 2 ; therefore V 2 = V 1 x C 1 /C 2 Where: V 1 = volume of tracer injected V 2 = unknown volume C 1 = Concentration of injected isotope (cpm/ml) C 2 = 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 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 V 1 C 1 = V 2 C 2 ; therefore V 2 = V 1 x C 1 /C 2 Where: –V 1 = volume of tracer injected –V 2 = unknown volume –C 1 = Concentration of injected isotope (cpm/ml) –C 2 = 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 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. Return to Table of ContentTable of Content