‘indicator- dilution’ method for blood flow determination
DESCRIPTION
Indicator Dilution that uses continuous infusion (Indicator – Oxygen)- samples from artery & Pulmonary artery Indicator Dilution method that uses rapid injection Dye dilution -indocyanine green – cardio green- dye injected to pulmonary artery – samples from artery Thermo Dilution – cold saline- injected to RA- temp measured in pulmonary arteryTRANSCRIPT
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• Indicator Dilution that uses continuous infusion (Indicator – Oxygen)- samples from artery & Pulmonary artery
• Indicator Dilution method that uses rapid injection• Dye dilution -indocyanine green – cardio green-
dye injected to pulmonary artery – samples from artery
• Thermo Dilution – cold saline- injected to RA- temp measured in pulmonary artery
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Indicator Dilution Method of Blood Flow Measurement
• An Indicator I is mixed with the blood with a known injection rate.
• The Concentration C of the indicator is measured after mixing.
• Then the flow,
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Indicator Dilution Method of Blood Flow Measurement
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Indicator Dilution Method of Blood Flow Measurement
• When a given quantity of m0 of an indicator is added to a volume V, the resulting concentration C of the indicator is given by• C = m0/V
• When an additional quantity m of indicator is then added, the incremental increase in concentration is • ΔC = m/V
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Indicator Dilution Method of Blood Flow Measurement
• When the fluid volume in the measured space is continuously removed and replaced, then in order to maintain a fixed change in concentration, a fixed quantity of indicator per unit time must be added continuously.
• ΔC = (dm/dt) / (dV/dt)
• Then the Flow,
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Fick Technique to measure blood flow from the heart
• Where
• F = Blood flow, liters/min
• dm/dt = consumption of O2, liters/min • Ca = arterial concentration of O2, liters/min
• Cv = venous concentration of O2, liters/min
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Fick Technique to measure blood flow from the heart
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Fick Technique to measure blood flow from the heart
• The blood returning to the heart from the upper half of the body has a different concentration of O2 from the blood returning fromthe lower half.
• The O2 concentration measured by the spirometer
• The arterial-venous concentration difference is measured by drawing samples through catheters placed in an artery and in the pulmonary artery.
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• Cv can be measure it in the pulmonary artery after it has been mixed by the pumping action of the right ventricle.
• The clinician can measure the concentration of the oxygenated blood Ca in any artery.
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Fick’s Technique - Advantage
• The Fick technique is nontoxic, because the indicator (O2) is a normal metabolite that is partially removed as blood passes through the systemic capillaries.
• The cardiac output must be constant over several minutes so that the investigator can obtain the slope of the curve for O2 consumption.
• The presence of the catheter causes a negligible change in cardiac output.
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Indicator Dilution Method that uses rapid injection
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Rapid-injection indicator-dilution curve
• Bolus is injected at time A• There is a transportation delay before the concentration begins
rising at time B. • After the peak is passed, the curve enters an exponential decay
region between C and D, which would continue decaying along the dotted curve to t1 if there were no recirculation.
• Recirculation causes a second peak at E before the indicator becomes thoroughly mixed in the blood at F.
• The dashed curve indicates the rapid recirculation that occurs when there is a hole between the left and right sides of the heart.
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• An increment of blood of volume dV passes the sampling site in time dt.
• quantity of indicator dm contained in dV is the concentration C(t) times incremental volume.
• Hence dm =C(t) dV . Dividing by dt, we obtain (dm/dt)= C(t) (dV/dt)
• dm= Fi C(t) dt
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• where t1 is the time at which all effects of the first pass of the bolus have died out (point E).
• The integrated quantity (∫ C(t) dt) ) is equal to the shaded area in Figure we can obtain it by counting squares or using a planimeter.
• If the initial concentration of indicator is not zero—as may be the case when there is residual indicator left over from previous injections( C(t) - > ∆ C(t) )
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Properties of Indicator
• (1) inert, • (2) harmless, • (3) measurable, • (4) economical,• (5) always intravascular.
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DYE DILUTION
• A common method of clinically measuring cardiac output is to use a
• colored dye, indocyanine green (cardiogreen).• It meets the necessary requirements for an indicator • The dye is available as a liquid that is diluted in isotonic
saline and injected directly through a catheter, usually into the pulmonary artery.
• About 50% of the dye is excreted by the kidneys in the first 10 min, so repeat determinations are possible.
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• The plot of the curve for concentration versus time is obtained from a constant-flow pump, which draws blood from a catheter placed in the femoral or brachial artery.
• Blood is drawn through a colorimeter cuvette which continuously measures the concentration of dye, using the principle of absorption photometry.
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Thermo Dilution
• Injecting a bolus of cold saline as an indicator. • A special four-lumen catheter is floated through
the brachial vein into place in the pulmonary artery.
• 1- A syringe forces a gas through one lumen; • 2-The cooled saline indicator is injected through
the second lumen into the right atrium. • 3- The third lumen carries the thermistor wires. • 4- Used for withdrawing blood samples.
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• The gas inflates a small, doughnut-shaped balloon at the tip.
• The indicator is mixed with blood in the right ventricle.
• The resulting drop in temperature of the blood is detected by a thermistor located near the catheter tip in the pulmonary artery
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