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Calculation of body fluid compartments
Calculation of body fluid compartments




For example, if 2 liters of a hypertonic 3.0 per cent sodium chloride solution are infused into the extracellular fluid compartment of a 70-kilogram patient whose initial plasma osmolarity is 280 mOsm/L, what would be the intracellular and extracellular fluid volumes and osmolarities after osmotic equilibrium? We can calculate the sequentialeffects of infusing different solutions on extracellular and intracellular fluid volumes and osmolarities. Both the intracellular and the extracellular volumes are increased by the addition of hypotonic fluid, although the intracellular volume increases to a greater extent.Ĭalculation of Fluid Shifts and Osmolarities After Infusion of Hypertonic Saline. If a hypotonic solution is added to the extracellular fluid, the osmolarity of the extracellular fluid decreases and some of the extracellular water diffuses into the cells until the intracellular and extracellular compart-ments have the same osmolarity (see Figure 25–6 C). The net effect is an increase in extracellular volume (greater than the volume of fluid added), a decrease in intracellular volume, and a rise in osmolarity in both compartments. Again, almost all the added sodium chloride remains in the extracellular compartment, and fluid diffuses from the cells into the extracellular space to achieve osmotic equilibrium. If a hypertonic solution is added to the extracellular fluid, the extracellular osmolarity increases and causes osmosis of water out of the cells into the extracellular compartment (see Figure 25–6 B). The sodium and chloride largely remain in the extracellular fluid because the cell membrane behaves as though it were virtually impermeable to the sodium chloride. The only effect is an increase in extracellular fluid volume (Figure 25–6 A). If an isotonic saline solution is added to the extracel-lular fluid compartment, the osmolarity of the extra-cellular fluid does not change therefore, no osmosis occurs through the cell membranes. Effect of Adding Saline Solution to the Extracellular Fluid






Calculation of body fluid compartments