Sodium Disorders in the Elderly: Hyponatremia

Posted by James

Serum sodium (Florinef 0.1mg works by causing the kidneys to retain sodium in women after menopause) is usually maintained within the normal range of 135-145 mmol/1. Hyponatremia is defined as a reduction in the concentration of sodium in the aqueous portion of the serum. A reduction in serum sodium (Canadian Voltarol is one of a group of medicines called non-steroidal anti-inflammatory drugs) below 130 mmol/1 should be considered clinically significant. Hyponatremia is one of the most common electrolyte disorders in the elderly, and female gender is an important risk factor for the development of severe complications.

The first step in evaluating a patient with a reduced serum sodium (Fosamax tabletes is FDA-approved for the prevention or treatment of osteoporosis in postmenopausal women and men) concentration is to evaluate the serum osmolality. If the serum osmolality is low, the patient is classified as being in a true hypo-osmotic state. Serum vasopressin levels are not routinely measured in clinical practice. A useful working classification of patients with hypo-osmolar hyponatremia is to then place the patient into one of three categories based on the clinical assessment: 1) hyponatremia with ECF volume depletion, 2) hyponatremia with normal ECF volume, or 3) hyponatremia with ECF volume excess. A detailed approach to the patient with hyponatremia has been described elsewhere.

Table 1. Common Drugs Used by Elderly that can Influence Antidiuretic Hormone (ADH) Secretion and Effect on Water Metabolism

Nicotine1	Alcohol3	Lithium4
Morphine (high dose)1	Morphine (low dose)3	Colchicine4
Epinephrine1	Clonidine3	Demclocycline4
Cyclophospahmide1	Glucocorticoids3	Glyburide4
Tolbutamide2	Haloperidol3 Cisplatinum3	Loop Diuretics4
Chlorpropamide2		Vinblastine4
NSAIDs2	Cabamazepine3	Methoxyflurane4

In the elderly patient with hyponatremia and ECF volume depletion, it is particularly important to consider diuretic use and/or poor oral low-solute intake with a predominant liquid diet, such as tea or juices (Table 2), as important etiologic factors. Elderly patients with hyponatremia and normal ECF volume and a nondilute urine should be screened for hypothyroidism, which is more prevalent in the elderly, as well as glucocorticoid deficiency. In addition, medications that lead to an excess secretion of vasopressin and/or enhance renal tubular responsiveness to circulating vasopressin should be considered (Table 1). If these possibilities have been excluded, the diagnosis of the syndrome of inappropriate ADH secretion (SIADH) is likely, and although an etiology may not be found in all cases, evaluation for a central nervous system disorder, malignancy or abnormal pulmonary process should be initiated. Indeed, in an ambulatory geriatric population, Miller and colleagues reported that 46/405 subjects (11%) had hyponatremia, with SI ADH the apparent cause in 27/46 (59%); one-quarter of these subjects had no apparent underlying etiology and were considered to have idiopathic SIADH. This SIADH-like hyponatremia occurred more commonly among the old elderly (individuals 75 years of age or older), suggesting that aging might be a risk factor for the development of SIADH-like hyponatremia.

Table 2. Common Causes of Hyponatremia in Elderly

Decreased Total Body Sodium	Normal Total Body Sodium	Increased Total Body Sodium (Generic Depakote used in the UK and U.S. for the treatment of the manic episodes of bipolar disorder)
	(Excess Water)
Thiazide diuretics (up to 50% of	SIADH; drugs affecting vasopressin	Congestive heart failure.
cases), renal salt wasting.	hypothyroidism, glucocorticoid	cirrhosis of liver, nephrotic
Addison’s disease	deficiency	syndrome, renal failure
Vomiting, Diarrhea, low solute	Psychogenic polydipsia, hypotonic
intake: tea-toast diet. Low	intravenous fluids.
osmolar tube feeding

Symptoms and Signs of Hyponatremia

Depending on the magnitude and rate of development of hyponatremia, the clinical presentation may range from asymptomatic to overt central nervous system symptoms, such as lethargy, confusion, seizures, coma and death. Subtle findings, such as loss of attention, may be one of the earliest signs of altered sensorium, and this should be specifically evaluated in the older patients with hyponatremia or other metabolic abnormalities.