Fluid shifts following 7% hypertonic saline (2400 mosmol/L) infusion.

Small volumes of hyperosmolar saline solutions may rapidly improve MAP and CO in hemorrhagic shock. In the present study, the effects of infusion of 7% NaCl on interstitial fluid volume and intracellular fluid volume were determined. In anesthetized, normovolemic rats either 7% NaCl (1.1 mL/100 g, intravenously), acetated Ringer's solution (10 mL/100 g), or no fluid (controls) were infused and extracellular volume (ECV) and plasma volume were determined in samples from skin, skeletal muscle, small intestine, liver, and lung. Intracellular volume was determined as local tissue water content minus ECV. Extracellular fluid volumes were 21.1 +/- .6 mL/ 100 g(mean +/- SEM; n = 6) (control animals), 26.1 +/- .4 mL/100 g (following 7% NaCl) (p < .05), and 32.8 +/- .5 mL/100 g (following Ringer's) (p < .05). Following 7% NaCl ECV increased by four to five times the infused volume. With 7% NaCl ECV in skin, muscle and intestine increased significantly, whereas cell volume was reduced by 10% in muscle and liver. Skeletal muscle, constituting > 40% of body mass with a large cell volume, was the main source for fluid mobilized by administration of 7% NaCl.