Failure of intravenous fluid therapies to decrease serum sodium levels in elderly hospitalized patients.

Elderly patients may have a tendency to develop hyponatremia due to sensitivity to stimuli that release ADH as well as an impaired ability to excrete a water load. We evaluated changes in serum sodium in elderly hospitalized patients who received various forms of intravenous fluid therapies. All patients were required to have a baseline serum sodium of 136-145 meq/L. Fourteen patients were enrolled in the study. The mean age was 82.9 +/- 6.8 years (mean +/- SEM). Thirty-six % were nursing home residents. Seventy-nine % were females. Seventy-two % received half normal saline and the remainder received normal saline as intravenous fluid therapy. The patients received a mean of 1098 +/- 145 mL of intravenous fluid per day, in addition to oral fluids. Mean follow up period was 5.9 days (3-10 days). Mean baseline serum sodium was 140.2 +/- 0.7 meq/L andmean follow up serum sodium was 141.4 +/- 0.9 meq/L. The m ean baseline BUN was 25 +/- 3.6 mg/dL and mean follow u BUN was 19.6 +/- 3.4 mg/dL. The mean baseline serum creatinine was 0.9 +/- 0.1 mg/dL and mean follow up creatinine was 0.9 +/- 0.1 mg/dL. The postintravenous fluid therapy serum sodium in the group receiving half normal saline was 141.7 +/- 0.7 meq/L and 140.8 +/- 3 meq/L in the normal saline group. No significant difference was observed between the pre and post fluid therapy for any of these paramenters (p > 0.05). Mean baseline plasma renin activity was 1.6 +/- 0.7 ng/ml/hour and fifty-seven % had PRA of less than 1 ng/ml/hour. Mean plasma aldosterone was 8.5 +/- 1.8 ng/mL and forty-two % were less than 5.5 ng/mL. Plasma ADH and ANP was 5.7 +/- 3.4 pg/mL and 83.6 +/- 26.9 pg/mL, respectively. Mean serum and urine osmolalities were 290 +/- 3.1 mOsm/kg and 471 +/- 57.7 mOsm/kg, respectively. No patient developed hyponatremia and 7 of the 14 patients experienced an increase in serum sodium during the follow up period. We conclude that many elderly patients hospitalized for acute medical illnesses either maintain a stable serum sodium or experience an increase in serum sodium. This occurs because total fluids administered to these patients are generally insufficient.