Hyponatremic syndromes

Hyponatremia

The serum sodium concentration reflects the osmolality of the extracellular fluid and provides no direct information about total body sodium content. Patients with hyponatremia may have decreased, normal, or increased total body sodium content. The first step in the approach to the patient with hyponatremia is measurement of plasma osmolality. Hyponatremia with normal plasma osmolality results from hyperlipemia or hyperproteinemia whereas hyponatremia with increased plasma osmolality results from hyperglycemia or mannitol infusion. Patients with hyponatremia and decreased plasma osmolality may be hypovolemic, hypervolemic, or normovolemic. The volume status of the patient is best determined by history, physical examination, and a few ancillary tests (e.g., total plasma protein concentration, hematocrit, blood pressure, central venous pressure). The clinical signs of hyponatremia are related more to the rapidity of onset than to the severity of the associated plasma hypoosmolality and reflect influx of water into the central nervous system. The main goals of treatment in hyponatremia are to manage the underlying disease and, if necessary, to increase serum sodium concentration and plasma osmolality.

Hyponatremia in tube-fed elderly men

Previous reports have described 5-20% prevalence of hyponatremia in extended care facilities, due largely to drugs or inappropriate antidiuretic hormone secretion. In our 400 bed VA extended care facility, 15 men with organic brain syndrome (Alzheimer's, multi-infarct dementia, anoxic encephalopathy or alcoholism) currently receive Isocal via gastrostomy as the sole source of nutrition. We noted intermittent hyponatremia in about half of these patients, and conducted a chart review to investigate the cause. Mean age was 68 yr (range 46-92); tube feeding duration was 3 mo.-3 yr; 266 Na concentrations were obtained from the charts. Simultaneous with these Na analyses, one of three diets prevailed: (A) mixed foods (3-6 g Na/day) orally before gastrostomy; (B) Isocal supplemented with NaCl to give 2 g Na/day; (C) unsupplemented Isocal providing 1 g Na/day. (B) and (C) had been randomly varied by rotating physicians. Serum Na was directly related to Na intake. On (A), Na was within normal range (135-145 mEq/l) in all men. One patient was hyponatremic during diet (B). During (C), eight patients were hyponatremic. Na was less than 135 mEq/l in 40% of all samples during diet (C) and less than 130 mEq/l in 14%. Changing from diet (A) or (B) to diet (C) caused nearly equivalent declines in Na and Cl; K and HCO-3 were unaffected. No hyponatremic patient took drugs known to cause hyponatremia, or had congestive heart failure, hypoalbuminemia, lipemia or fasting hyperglycemia. At the end of the study, four hyponatremic men were changed from (C) to (B); serum Na became normal in all four patients, without edema or hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurological aspects of hyponatraemia

Hyponatraemia is a common biochemical finding, but clinical features due to it are infrequent. They are most likely to occur when the plasma sodium concentration has fallen quickly to below 120 mmol/litre. In a study of 73 hyponatraemic individuals, it was possible to identify four categories of patient, the clinical features becoming more severe as the sodium level fell. In 25 instances there were no effects (mean plasma sodium 118·3 mmol/litre), in a further 25 cases there was confusion only (mean plasma sodium 117·1 mmol/litre), in 13 there were focal neurological signs and in 10 there were convulsions (mean plasma sodium 110·8 mmol/litre). In the group with convulsions there were six deaths, the four survivors all being young women. The 13 cases of ‘focal’ neurological signs included three instances each of hemiparesis and monoparesis, seven of extra-pyramidal disturbance and six of cerebellar ataxia. All these abnormalities resolved when the plasma sodium concentration rose to 125 mmol/litre.

Active measures to raise the plasma sodium level are only needed when there have been convulsions and the aim should be to achieve a value no higher than 120 mmol/litre. In other cases, the only treatment required is to restrict fluid intake.

Coma from hyponatremia following transurethral resection of prostate

Even though hyponatremia may occur following transurethral resection of the prostate (TURP), only 14 patients of a large TURP population deteriorated to a comatose state as a result of hyponatremia. These patients were generally older, with larger prostates, and longer resection times than the average for transurethral resection of the prostate. They also consistently had serum sodium levels postoperatively of near 120 mEq./L. or below. It was noted that obtundation can occur immediately or be delayed several hours. Even though no deaths occurred, awareness of the possibility of post-TURP hyponatremia and prompt treatment with hypertonic saline were shown to reduce morbidity significantly.