Question #296
Which of the following markers can be used to estimate the intravascular volume?
Evan's Blue dye binds to plasma proteins and thus remains within the intravascular compartment. It is also non-toxic and is cleared from the body at a relatively modest rate, all making it useful for estimating plasma volume.
Blood volume may be calculated from plasma volume using the equation
blood volume = plasma volume / (1 - haematocrit)
This equation perhaps makes more intuitive sense cross-multiplied.
Tritiated water will distribute itself amongst both intracellular and extraceullular fluid compartments and can thus be used to estimate the total body water volume.
Thiosulphate ions remain in the extracellular fluid compartment and this marker can thus be used to estimate the extracellular fluid volume.