5 g mannitol was injected intravenously. 40% of mannitol is excreted. After equilibrium, plasma concentration of mannitol is 30 mg%. Calculate extracellular fluid volume.: (A) 10 L, (B) 14 L, (C) 18 L, (D) 24 L
Answer is A. The volume of water in different compament can be measured by volume of distribution principle (indicator dilution principle). Where v = Volume of fluid Q = Quantity of indicator given C = Concentration of the indicator e = The amount of indicator which has either been lost or metabolized 30 mg% = 30 mg/ 100 mL = 300 mg/ L = 0.3g/L Quantity of mannitol excreted = 5 * 40/100 = 2 g ECF volume = 5 - 2 / 0.3 = 3 / 0.3 = 10 L