The aldosterone response to surgery and the relationship of this response to postoperative sodium retention

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Abstract
To investigate whether the aldosterone response to surgery is ‘inevitable’ and whether it is the prime cause of postoperative sodium retention, 30 patients undergoing uncomplicated cholecystectomy were givaen four different postoperative intravenous intakes (either ‘low’ or ‘high’ sodium, with and without dextran). Patients on the low sodium intake–a conventional intake of approximately 75 mmol of sodium daily – had a sixfold increase in their plasma aldosterone levels on the day of operation, which slowly declined to the preoperative level by the fifth day after operation, Patients on a high sodium intake, which was between two and three times the low sodium intake, showed only a modest rise (two-fold), which returned to the preoperative level within 8 h of operation. These aldosterone responses appeared to be caused by at least two stimuli, with the evidence suggesting that ACTH and renin were both involved. Patients on the high sodium intake had the highest positive sodium balance, amounting to approximately 400 mmol of sodium retained by day 4 after operation, despite the fact that the plasma aldosterone level had returned to the preoperative level within 8 h of operation, and thereafter remained below it. No clear evidence was found to show that the plasma aldosterone level had any significant relationship to the amount of sodium each patient retained. The sodium retained was found to be a similar proportion of the sodium intake whether the intake was low or high, the addition of dextran making no consistent difference. Analysis of the data produced the incidental finding of an increasingly significant correlation, over the 5 postoperative days studied, between the proportion of sodium retained and the patient's preoperative systolic blood pressure. It has long been known that patients with a raised blood pressure excrete a sodium load more rapidly than normotensive patients, but this effect on sodium balance after operation has not previously been recorded.