The Indicator Dilution Method Measures Fluid Compartment Size

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The indicator dilution method can be used to determine the size of body fluid compartments (see Chapter 14). A known amount of a substance (the indicator), which should be confined to the compartment of interest, is administered. After allowing sufficient time for uniform distribution of the indicator throughout the compartment, a plasma sample is collected. The concentration of the indicator in the plasma at equilibrium is measured, and the distribution volume is calculated from this formula

Volume = Amount of indicator/ Concentration of indicator

If there was loss of indicator from the fluid compartment, the amount lost is subtracted from the amount administered.

To measure total body water, heavy water (deuterium oxide), tritiated water (HTO), or antipyrene (a drug that distributes throughout all of the body water) is used as an indicator. For example, suppose we want to measure total body water in a 60-kg woman. We inject 30 mL of deuterium oxide (D2O) as an isotonic saline solution into an arm vein. After a 2-hr equilibration period, a blood sample is withdrawn, and the plasma is separated and analyzed for D2O. A concentration of 0.001 mL D2O/mL plasma water is found. Suppose during the equilibration period, urinary, respiratory, and cutaneous losses of D2O are 0.12 mL. Substituting these values into the indicator dilution equation, we get

Total body water = (30 - 0.12 mL D2O) X 0.001 mL D2O/mL water = 29,880 mL or 30 L

Therefore, total body water as a percentage of body weight equals 50% in this woman.

To measure extracellular water volume, the ideal indicator should distribute rapidly and uniformly outside the cells and should not enter the cell compartment. Unfortunately, there is no such ideal indicator, so the exact volume of the ECF cannot be measured. A reasonable estimate, however, can be obtained using two different classes of substances: impermeant ions and inert sugars. ECF volume has been determined from the volume of distribution of these ions: radioactive Na+, radioactive Cl_, radioactive sulfate, thio-cyanate (SCN~), and thiosulfate (S2O32-); radioactive sulfate (35SO42-) is probably the most accurate. However, ions are not completely impermeant; they slowly enter the cell compartment, so measurements tend to lead to an overestimate of ECF volume. Measurements with inert sugars (such as mannitol, sucrose, and inulin) tend to lead to an underestimate of ECF volume because they are excluded from some of the extracellular water—for example, the water in dense connective tissue and cartilage. Special techniques are required when using these sugars because they are rapidly filtered and excreted by the kidneys after their intravenous injection.

Cellular water cannot be determined directly with any indicator. It can, however, be calculated from the difference between measurements of total body water and extracellular water.

Plasma water is determined by using Evans blue dye, which avidly binds serum albumin or radioiodinated serum albumin (RISA), and by collecting and analyzing a blood plasma sample. In effect, the plasma volume is measured from the distribution volume of serum albumin. The assumption is that serum albumin is completely confined to the vascular compartment, but this is not entirely true. Indeed, serum albumin is slowly (3 to 4% per hour) lost from the blood by diffusive and convective transport through capillary walls. To correct for this loss, repeated blood samples can be collected at timed intervals, and the concentration of albumin at time zero (the time at which no loss would have occurred) can be determined by extrapolation. Alternatively, the plasma concentration of indicator 10 minutes after injection can be used; this value is usually close to the extrapolated value. If plasma volume and hema-tocrit are known, total circulating blood volume can be calculated (see Chapter 11).

Interstitial fluid and lymph volume cannot be determined directly. It can be calculated as the difference between ECF and plasma volumes.

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Responses

  • tesmi
    What volume cannot be measured using indicator dilution technique?
    8 years ago
  • romilda
    Who discovered indicator dilution method of estimation extracellular fluid?
    8 years ago
  • mentha t
    What is indicator dilution techniques,how is it applied in the measurement of total body water?
    3 years ago
  • Quintilia
    How to measure total body water using triated water?
    3 years ago
  • Mathilda
    How is indicator dilution technique applied in the measurement of total body water?
    3 years ago
  • sirpa
    What indicators are used in measuring the volume of body fluid compartment?
    3 years ago
  • chica
    What is Dilution method in fluid compartments?
    3 years ago
  • arsi haapalainen
    How to measure body fluids using indicator dilution method?
    3 years ago
  • dehab
    What is dye dilution method in body fluid?
    3 years ago
  • claudia
    WHAT is indicator dilution method in.measurement of body fluid?
    3 years ago
  • murron
    What indicator is used for measuring body water in dilution technique?
    2 years ago
  • nick
    Why deuterium used in indicator dilution?
    2 years ago
  • dirk
    What is the indicators of fluid compatment?
    2 years ago
  • christian
    What are the indicators for the measurement of plasma?
    2 years ago
  • gabriele
    What are substance use to measure body fluids compartments with there suitability limitations?
    2 years ago
  • Bellisima Roper
    How to measure body volume using indicstor dilution method?
    2 years ago
  • Henna
    How is water measured in our body using the dilution principle?
    2 years ago
  • ansegar
    How to measure body water using dilution principle?
    2 years ago
  • niklas
    How body fluid is measured according to dilution principle?
    2 years ago
  • Szymon
    How to measure body fluid using dilution method?
    2 years ago
  • stephan
    Can water be used to dilute with power indicator?
    2 years ago
  • anneli ketterer
    What dye is the most accurate in measuring ECF fluid?
    2 years ago
  • Filibert
    Can ECF be estimated by the dilution of D2o?
    2 years ago
  • Amanda
    Why D2O is used as indicator to measure Total body water?
    2 years ago
  • catherine
    Can total body water be measured by an indicator using dilution technique aminopyrine?
    2 years ago
  • wanda
    Is indicator dilution method used in measuring total bodywater?
    1 year ago
  • SEAN
    Why is indicator dilute principle use in the measurement of body fluid volume?
    1 year ago
  • Yolanda
    Why indicator dilution principle is used in measurement of body fluid volume?
    1 year ago
  • mareta
    Why is indicator dilution principle used in measuring body fluid volume?
    1 year ago
  • destiny scott
    Why do we use indicator dilute principle to measure body fluid volume?
    1 year ago
  • Lea
    Why is indicator dilution method principle used in measurement of body fluid?
    1 year ago
  • dario
    Can total body water be measured directly with a single indicator?
    1 year ago
  • Tommy Kattilakoski
    What indicators can be.used to measure total body water?
    1 year ago
  • doreen
    How is indicator dilution technique applied in the measurements of extracellular fluid?
    10 months ago
  • wolfgang
    How to determime body fluid compartment using dye dilution method?
    8 months ago
  • Tina
    How to measure indicator dilution method intra cellular fluid volume?
    7 months ago
  • How to measure the conc of d20 in water in measuring total body fluid?
    6 months ago
  • james
    How to mesure body fluid compatment?
    3 months ago
  • macaria
    How the dilution method works in measuring body compartments?
    3 months ago

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