Hyponatremia Case Study

A 72-year-old male presents to his physician, complaining that he is coughing blood-tinged sputum. The patient states that he has been a heavy smoker all of his life and has coughed up yellow sputum every morning for years now, but the sputum has never had blood in it before. On review of systems, the patient says that he has been feeling tired recently and has lost 5.4 kg (12 lb) despite no change in his diet.

Vital signs: Temp 37.2ºF (99°F), blood pressure 110/76 mmHg, heart rate 88 beats/min, respiratory rate 14 breaths/min.

Physical examination is unremarkable with no evidence of leg edema, lung crepitations, heart S3 sound, or ascites. Skin turgor is normal. Laboratory studies show a normal urinalysis and CBC, with comprehensive chemistry

Symptoms are not usually present in mild chronic hyponatremia, as is seen with this patient. Symptoms are more likely when there is a rapid decrease in serum sodium levels and when sodium is < 120 mEq/mL. In asymptomatic SIADH, fluid restriction will restore the serum sodium to normal. Treatment of the small cell carcinoma with chemotherapy should give a permanent end to the source of the ADH. Restriction to 50% to 60% of daily fluid requirements may be required to achieve the goal of inducing negative water balance. In general, fluid intake should be less than 800

The vasopressin receptor antagonists may provide an alternative treatment for SIADH. They produce a selective water diuresis without affecting sodium and potassium excretion. Conivaptan specifically blocks the V2 receptor. The ensuing loss of free water tends to correct the hyponatremia. However, thirst increases significantly with these agents, which may limit the rise in serum sodium. Also, they may cause too rapid a rise in sodium levels, they are expensive, and there may be adverse effects. Water restriction is a safe and simple first choice.

Choice "C" is not the best answer. More aggressive therapy is indicated in patients who have symptomatic or severe hyponatremia. In this setting, initial therapy usually consists of hypertonic saline with or without vasopressin receptor antagonists. The rate of correction is important because too-rapid correction of severe hyponatremia can lead to osmotic demyelination (aka central pontine demyelinosis). One group that is probably not at risk for this complication is patients with hyperacute hyponatremia that develops over a few hours due to a marked increase in water intake, as may be seen in marathon runners, psychotic patients, and users of 3,4-methylenedioxy-methamphetamine (MDMA;