5/2/2023 0 Comments Plasma volume calculator![]() To calculate the intracellular fluid volume subtract the extracellular fluid volume from the total fluid volume. To calculate the interstitial (fluid not in the cells and not in the blood) fluid volume, subtract the plasma volume from the extracellular volume. To measure the extracellular fluid volume, use a cell inpermeant marker substance such as inulin or mannitol that will equilibrate everywhere except in the cells (it is possible to make inulin and mannitol radioactive). One such marker is Evan's Blue, a dye which binds to plasma proteins. Therefore, to measure the volume of the blood plasma fluid compartment, you need a marker which equilibrates throughout the blood supply and nowhere else. M U is usually calculated from C U, the concentration of marker lost in the urine and V U, the volume of the urine thus: M U = C U. Plasma volume Total blood volume, mL × (1 hematocrit / 100) RBC volume represents the quantity of the red blood cells component of whole blood and is derived from hematocrit and total blood volume: Total blood volume is estimated depending on patient characteristics: For this category, the total blood volume Nadler’s formulas are used. Where V is the volume of the body fluid compartment, M is the mass of marker injected, M U is the mass of marker lost in the urine during equilibration and C is the measured concentration of the marker. As this is not possible (the kidney will excrete everything dissolved in the bloodstream) the calculation must correct for excretion. Plasma substitutes should not be used to maintain plasma volume in. To be an absolutely perfect marker, the substance should also not be excreted. Acute severe hyperkalaemia (plasma-potassium concentration 6.5 mmol/litre or greater. Therefore: if you know the mass of marker injected into the body and are able to measure the marker concentration once equilibration is complete, you can calculate the volume of the compartment occupied by the marker. Given that concentration (C) = mass (M) / volume (V) it should be obvious that: Furthermore, it must be possible to measure the concentration of the marker once equilibration is complete.Tritiated ( 3H) water is a good marker for the whole body fluid compartment because it diffuses throughout the body, it is chemically identical to normal water and it is easy to measure the equilibrium concentration because 3H water is radioactive. To be a perfect marker a substance must also not be metabolised. To measure the volume of any fluid compartment within the body you must inject or infuse a marker substance that will equilibrate (diffuse freely to a uniform concentration) throughout this compartment. Body fluid compartments calculations Body Fluid compartments Measuring Body Fluid Compartments ![]()
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