Question

Using these data-Calculate Interstitial Volume (ISV) in liters :

Amount ofD20 injected, corrected for loss = 40 mg

Plasma D20 concentration = 1 mg / L

Amount of inulin injected, corrected for loss = 20 mg

Plasma inulin concentration = 2 mg/L

Amount of Evan's Blue injected, corrected for loss = 2.5 mg

Plasma Evan's Blue concentration = 1 mg/ L

Hematocrit (Hct) = 40%

(please show work)

Answer 1

Total Body Water or TBW is 60% of body weight. TBW is distributed between two major compartments: intracellular field (ICF) and extracellular fluid (ECF).ICF is 2/3 of TBW and ECF is 1/3 of TBW. ECF is then subdivided into two compartments: interstitial fluid and plasma.

A marker substance is one which according to its physical characteristics distributes only in a specific fluid compartment. For example:

• D2O is a marker for TBW (Total Body Water).
• Inulin is a marker for ECF (Extracellular fluid)
• Evan's blue is a marker for plasma.

Volume distribution of a marker substance is calculated as:

where is the amount of marker injected

is the concentration of marker measured in the fluid compartment

Interstial volume is measured as:

Therefore, the interstitial volume is 7.5L