Hemorrhage in Normal Man

Abstract

Infusion of 20% mannitol produces a sudden dislocation of body fluid characterized by a transient increase in plasma volume with fall in the hematocrit, fall in the peripheral concentration of erythrocytes, followed by a slower and more marked increase in the extracellular fluid volume. There Is an early fall in Na concentration. These events, in turn, are followed by a solute diuresis characterized by urine of a fixed osmolality (about 600-700 mOsm.), and at rates of 4-5 ml/min. This urine has a water: Na ratio higher than plasma, and its continued output under the stimulus of repeated mannitol infusions will produce severe hypernatremia. The distribution of water, electrolyte, and solute at the close of the mannitol infusion indicates that the mannitol-attracted water has largely been excreted; the total new crystalloid solute presented by infusion has largely been excreted; there has been a net loss in body water. The total new water appearing in extracellular fluid plus urine Is less than that predicted from the dilution of the injected solute because the kidneys are capable of excreting the solute at a concentration higher than that ?bserved in plasma. Following cessation of the infusion there Is a continued dispersal of mannitol and water out of the plasma volume, and a continued excretion of water, salt and crystalloid at a brisk rate. The over-all dehydration produced by these events may be noticeable as late as the following day, when continued hyperprotelnemia is observed and Na concentration is begining to rise. Following hemorrhage the trans capillary refill tends to be incomplete when mannitol is used, probably due to this dehydrating effect. A prolonged restriction of Na excretion is likewise noted. Mannltol must be employed with full knowledge of its drastic effects; its toxic side effects (hyponatremia, later hypematremia, plasma volume increment and renal tubular changes in chronic administration) need not be encountered if the material is used briefly and Intelligently in the volume-restricted patient.