Hyponatremia is a low concentration of sodium in the blood (< 135 mEq/L). It most commonly occurs as a complication of other, potentially serious, medical issues: heart failure, pneumonia, and liver failure.
It is the most common electrolyte abnormality observed in clinical practice, and it is associated with a prolonged hospital stay and higher risk for readmission.
Hypovolemic hypotonic hyponatremia
usually indicates concomitant solute depletion, with patients presenting with orthostatic symptoms. The pathophysiology underlying hypovolemic hypotonic hyponatremia is complex and involves the interplay of carotid baroreceptors, the sympathetic nervous system, the renin-angiotensin system, antidiuretic hormone (ADH) secretion, and renal tubular function.
Normovolemic hypotonic hyponatremia
is common among patients who are hospitalized. It is associated with nonosmotic and non-volume-related syndrome of inappropriate ADH secretion secondary to various clinical conditions, including:
• CNS disturbances (e.g., hypopituitarism )
• major surgery
• pulmonary tumors
• certain medications
In many cases the recognition is entirely incidental. Clinical symptoms may result from the cause of hyponatremia or the hyponatremia itself. Many medical illnesses, such as chronic heart failure, liver failure, renal failure, or pneumonia, may be associated with hyponatremia. These patients frequently present because of their primary disease (dyspnea, jaundice, uremia, or cough).
Evident neurologic symptoms most often are due to very low serum sodium levels (usually < 115 mEq/L), resulting in intracerebral osmotic fluid shifts and brain edema. Symptoms range from nausea and malaise, with mild reduction in the serum sodium level, to vomiting, lethargy, decreased level of consciousness, muscle spasms, headache, and seizures and coma.
A European clinical practice guideline defines hyponatremia according to serum sodium concentration and duration:
• Mild: 130-135 mmol/L
• Moderate: 125-129 mmol/L
• Profound: < 125 mmol/L
• Acute: lasting < 48 hours
• Chronic: lasting ≥ 48 hours, or duration cannot be classified
See reference for more information.
Adapted from Medscape Drugs & Diseases. fast five quiz: hyponatremia essentials. Internet. Available at https://reference.medscape.com/viewarticle/919756?src=wnl_fastquiz_191026_mscpref&uac=6705FY&impID=2140669&faf=1 Accessed on January 25, 2020. To view the entire article and all other content on the Medscape News and Perspective site, a free, one-time registration is requi