Resources for Evaluating, Diagnosing, and Managing Patients with Hyponatremia

Here you will find a brief roundup of useful online resources for clinicians who treat patients with hyponatremia.

The BMJ Best Practice series offers “the latest research evidence, guidelines and expert opinion -- presented in a step-by-step approach, covering prevention, diagnosis, treatment and prognosis.” The information is designed to provide “a second opinion in an instant, without the need for checking multiple resources.” The Best Practice resource for evaluating hyponatremia offers a concise summary of the effects of hyponatremia, the five main types (hypovolemic hyponatremia, euvolemic hyponatremia, hypervolemic hyponatremia, hypertonic hyponatremia, and pseudohyponatremia), the CNS effects of this condition, the etiology of hyponatremia, a step-by-step guide to diagnosis, differential diagnosis tips and advice, and more. Users must register with the site to access the full version of this resource.

This comprehensive article from Medscape offers in-depth information on the pathophysiology and epidemiology of hyponatremia, presentation, differential diagnosis, workup, treatment, and follow up. Clinicians are reminded that “patients may present for medical attention with symptoms related to low serum sodium concentrations. However, many patients present due to manifestations of other medical comorbidities, with hyponatremia being recognized only secondarily. For many people, therefore, the recognition is entirely incidental. Patients may develop clinical symptoms due to the cause of hyponatremia or the hyponatremia itself.” The workup section notes that there are three “essential laboratory tests in the evaluation of patients with hyponatremia that, together with the history and the physical examination, help to establish the primary underlying etiologic mechanism.” The three tests are urine osmolality, serum osmolality, and urinary sodium concentration. The treatment section covers the use of intravenous fluids and sodium restriction, pharmacologic treatment options, and dietary modifications. Medications covered include loop diuretics and vasopressin antagonists.

The UpToDate page on the evaluation of the patient with hyponatremia notes that hyponatremia “is commonly defined as a serum sodium concentration below 135 meq/L, but can vary to a small degree in different clinical laboratories. In virtually all patients, hyponatremia results from the intake (either oral or intravenous) and subsequent retention of water. A water load will, in normal individuals, be rapidly excreted as the dilutional fall in serum osmolality suppresses the release of antidiuretic hormone ADH, also called vasopressin, thereby allowing excretion of the excess water in a dilute urine.” The diagnostic approach to the patient with hyponatremia outlined here covers the history and physical exam, essential lab tests (including fractional excretion of sodium, serum uric acid and urea concentration, and urine to serum electrolyte ratio). The page also provides links to a review of the causes of hyponatremia and an overview of the treatment and management of hyponatremia.

A recent issue of the newsletter of the American Society of Health-System Pharmacists (ASHP) offers a wealth of useful information on the classification and management of hyponatremia in hospitalized patients. The authors note that “the majority of cases of hyponatremia are dilutional and characterized by increased total body water and near normal total body sodium. Dilutional hyponatremia may be further classified as (1) hypervolemic if total body water is greatly increased and total body sodium is increased or (2) euvolemic if total body water is slightly increased and total body sodium is normal. Heart failure is a common cause of hypervolemic hyponatremia, and edema typically is present. Edema usually is absent in euvolemic hyponatremia, the most common cause of which is syndrome of inappropriate antidiuretic hormone (SIADH). Tumors and a wide variety of disorders, conditions, and medications (eg, carbamazepine, SSRIs) can lead to SIADH.”

The ASHP newsletter covers the pros and cons of traditional pharmacotherapies for hyponatremia, as well as the newer vasopressin receptor antagonists. Readers will also find answers to frequently asked clinical questions, such as:

• Should fluids be restricted during vaptan use?
• If a vaptan were initiated in a patient with heart failure, would you discontinue therapy at the time of resolution of symptoms, after a specific increase in serum sodium concentration, or both?
• Is fluid restriction the most cost-effective method for managing hyponatremia in hospitalized patients?