Body Water Distribution After Operation

The effect of a major surgical procedure on the distribution of body water was investigated in two groups of patients. The first group of four patients did not receive any salt during the first 24 hours following operation, while the second group of five patients received a moderate amount of isotoric saline solution during this period. For seven days prior to operation, the patients were maintained by bed rest and a daily intake of 100 milliequivalents of sodium and 100 milliequivalents of potassium. A multiple isotope dilution technique was used, before and after operation, to measure red cell mass, plasma volume, extracellular water, total body water and total exchangeable sodium. In addition, the aldosterone secretion rate was measured, both before and after operation, to assess the physiologic control of the extracellular water volume. In the patients who did not receive any salt, the mean extracellular water volume decreased following operation from 39.7 to 37.5 per cent of the total body water; a mean decrease of 0.9 liter while the aldosterone secretion rate increased significantly, p less than 0.02, by 101 per cent from 206 to 414 micrograms per day. In the second group of patients who received an average of 1.3 liters of isotonic saline solution during the first 24 postoperative hours, the extracellular water increased from 37.9 to 42.8 per cent of total body water; a mean increase of 1.1 liters p less than 0.02. The mean aldosterone secretion rate in this group of patients increased by only 13 per cent from 167 to 188 micrograms per day. The blood volume did not change in either group as a result of operation. These data support the hypothesis that, following operation, sequestration of extracellular water occurs within the injured tissues, necessitating the postoperative infusion of a moderate amount of a balanced salt solution.