Perioperative Care; Fluid and Electrolyte

The amount and direction of movement between the interstitium and the capillary are determined by the interaction of (1) capillary hydrostatic pressure, (2) plasma oncotic pressure, (3) interstitial hydrostatic pressure, and (4) interstitial oncotic pressure.

If capillary or interstitial pressures are altered, fluid may abnormally shift from one compartment to another, resulting in edema or dehydration.

Fluid is drawn into the plasma space whenever there is an increase in the plasma osmotic or oncotic pressure. This could happen with administration of colloids, dextran, mannitol, or hypertonic solutions.