Assessment of Hormonal Disorders of Water Metabolism

Hyponatremia among the institutionalized elderly in 2 long-term care facilities in Taipei

BACKGROUND

Hyponatremia is common in the institutionalized elderly, and syndrome of inappropriate antidiuretic hormone secretion was deemed the most important etiologic factor. The purpose of this study was to evaluate the prevalence and etiologic factors of hyponatremia among institutionalized elderly and to explore its association with nutritional status.

METHODS

Subjects in 2 private long-term care facilities (LTCFs) participated in this study. Periodic nutritional evaluations, including anthropometric measurements and serial laboratory examinations, were performed every 6 months. When hyponatremia was identified, serum osmolality, serum levels of cortisol, thyrotropin, antidiuretic hormone, urine osmolality, and electrolyte profile were done instantly. Water loading tests were performed for subjects with euvolemic, hypo-osmolar hyponatremia. Nutritional status (i.e. hemoglobin, serum albumin, serum total cholesterol, body mass index [BMI], and mean body weight loss within 6 months) was compared between hyponatremic and normonatremic subjects during hyponatremic episodes and at follow-up (6 months later).

RESULTS

In total, 67 (mean age = 77.2 +/- 8.8 years, M/F = 45/22) LTCF residents were enrolled. The prevalence of hyponatremia was 31.3% (21/67) during the 6-month period, and 62.5% of these cases were related to reset osmostat. In addition, BMI was similar between hyponatremic and normonatremic subjects during hyponatremic episodes (19.1 +/- 3.2 vs 20.5 +/- 4.0 kg/m2, p = 0.16), but became significantly lower in hyponatremic subjects 6 months later (18.5 +/- 3.2 vs 20.8 +/- 4.2 kg/m2, p = 0.027). However, the mean body weight loss during the 6-month follow-up was similar (3.0% vs 0.8%, p = 0.25). Furthermore, hemoglobin and serum levels of albumin were similar between groups during hyponatremic episodes and at follow-ups, but serum levels of total cholesterol were significantly lower in hyponatremic subjects on both occasions (166.9 +/- 30.5 vs 190.2 +/- 38.2 mg/dL, p = 0.016 during hyponatremic episodes and 153.6 +/- 29.4 vs 182.8 +/- 35.5 mg/dL, p = 0.003 at follow-up).

CONCLUSION

About a third of LTC-dwelling elderly would experience hyponatremia during the 6-month period, and 62.5% of them were due to reset osmostat. The relationship between hyponatremia and undernutrition deserves further investigation.

Hyponatremia in a nursing home population

OBJECTIVE

To determine the prevalence of hyponatremia in a nursing home population and to identify clinical factors that increase the risk for development of hyponatremia.

DESIGN

Retrospective and prospective record review.

SETTING

A Veterans Affairs nursing home care unit.

PATIENTS

One hundred nineteen residents, who ranged in age from 60 to 103 years. Sixty ambulatory patients, 62 to 91 years of age, who attended a geriatric medicine outpatient clinic served as a reference population.

MEASUREMENTS

Most recent serum sodium, creatinine, BUN, and all serum sodium determinations during the preceding 12 months; clinical diagnoses, diet, medications, and significant events at the time of recorded hyponatremic episodes; response to acute water loading in a subset of patients; number of deaths in the 12 months following entry into the study.

RESULTS

In the 119 nursing home patients, ages 60 years or older, the most recent serum sodium identified 18% who were hyponatremic, compared with a prevalence of 8% in similarly aged ambulatory patients. When all serum sodium determinations for the previous 12 months were examined, 53% of the nursing home patients had at least one episode of hyponatremia during this time period. There was a high incidence of central nervous system (CNS) and spinal cord disease in the total nursing home population. Episodes of hyponatremia were frequently associated with an increased intake of fluids, given either orally or intravenously, and with tube feeding. Water load testing revealed abnormal water handling consistent with the syndrome of inappropriate antidiuretic hormone (ADH) secretion in 18 of 23 patients who had a history of hyponatremia. Seventeen percent of the patients with hyponatremia died over the following 12 months, compared to a death rate of 21% in the normonatremic patients.

CONCLUSIONS

Hyponatremia is a common occurrence in nursing home residents and may be a consequence of abnormal ADH secretion resulting from CNS disease. Exposure to increased fluid intake, or to a low sodium tube-feeding diet, can lead to the onset of hyponatremia or to a worsening of an already present low-serum sodium concentration.