<prompt> In a study to detect extracellular fluid volume, 10 gm mannitol was injected by intravenous route and after waiting for adequate time for equilibration of levels, concentration was measured as 50 mg100 ml. In this time, 10 mannitol was excreted. What is the calculated volume of ECF?10 Litres18 Litres42 Litres52 Litres  <response>: Ans. b. 18 Litres Ref. Ganong 24e p2Out of 10 gm mannitol, 10 was excreted.Hence, amount of mannitol distributed in ECF 10-1 9 gmGiven concentration of mannitol in ECF 50 mg100 mlVolume of ECF AmountConcentration 9 g50 mg x 100 ml 18 LBody FluidsWater constitutes approximately 60 of total body weightQ.Of this 60, 40 is present in cells in the form of intracellular fluid ICF and 20 is present outside the cells in the form of extracellular fluid ECFQ.20 of body weight water in ECF is divided into interstitial fluid 15 of body weight and plasma 5 of body weightQ.Body FluidsTotal Body Water 60 of body weightQIntracellular fluid ICFExtracellular fluid ECF 23rd of TBWQ 40 of body weight 13rd of TBW 20 of body weightQECFPlasmaInterstitial fluid 25 or 14th of ECF 5 of body weightQ 75 or 34th of ECF 15 of body weightQMost of the fluids are calculated directly from dilution methods, except for ICF interstitial fluids. Both of these are calculated indirectly by calculating other body fluids.ICF Total body water volume - ECF volumeInterstitial fluid ECF volume - Plasma volumeFluid volumeindicator usedTotal body water volume Deuterium oxide: D20 MC usedQ Tritium oxideQ AmlnopyrineQ AntipyrineQExtracellular fluid volume Inulin most accurateQ Sucrose Mannitol Sodium thiosulphatePlasma volume Evans blueQ Serum albumin labeled with radioactive iodineQ 1-125Red cell volume Cr-51 labeled RBCQ 