THE RÔLE OF THE EXTRACELLULAR FLUID IN THE MAINTENANCE OF A NORMAL PLASMA VOLUME

Abstract

The quantity of plasma protein was reduced in dogs by injuring the capillaries of the extremities by a 5-6 hr. period of arterial occlusion produced with tourniquets. Massive intravenous infusions of physiological saline soln. after the release of the tourniquets maintained the circulation at a normal level. There was continued plasma loss in the damaged extremities and the plasma protein level fell markedly. If the saline infusion was stopped in the first few hrs., the plasma vol. decreased in size and circulatory insufficiency developed. If the saline infusion was continued until generalized edema developed, no further tendency to hemoconc. was noted, in spite of the fact that the quantity of circulating protein was still 50% or more below the control level. The plasma volume and circulatory dynamics remained normal. Un- injured anesthetized dogs were given large amts. of physiological saline soln. intravenously. They developed generalized edema but showed much less decrease in total circulating protein than did the injured animals. The quantity and pressure of the extracellular fluid is as important in determining the plasma vol. as is the quantity of circulating plasma protein. A marked decrease in the osmotic pressure of the plasma protein can be compensated by a marked increase in the pressure and volume of the extracellular fluid, without affecting the circulation or the size of the plasma volume.