From the Guidelines
The workup of hyponatremia in ICU patients should begin with a thorough assessment of volume status, as this guides management, and correction of sodium should be done slowly, aiming for no more than 6-8 mEq/L in 24 hours to prevent osmotic demyelination syndrome, as recommended by the most recent guidelines 1.
Key Steps in Workup and Management
- Obtain serum and urine osmolality, urine sodium, and assess the patient's volume status through physical examination, hemodynamic parameters, and fluid balance records.
- For hypovolemic hyponatremia, administer isotonic saline at 100-150 mL/hour until euvolemia is achieved.
- In euvolemic hyponatremia, fluid restriction to 800-1000 mL/day is the mainstay of treatment, with consideration of 3% hypertonic saline for severe cases (Na <120 mEq/L or symptomatic).
- For hypervolemic hyponatremia, restrict fluid and sodium intake and administer loop diuretics like furosemide 20-40 mg IV every 12 hours.
Considerations for Correction of Sodium
- Correct sodium slowly, aiming for no more than 6-8 mEq/L in 24 hours to prevent osmotic demyelination syndrome.
- Frequent monitoring of serum sodium (every 2-4 hours initially) is essential.
- Consider underlying causes such as medications (thiazides, SSRIs), adrenal insufficiency, hypothyroidism, or SIADH.
- In ICU patients, critical illness itself can cause SIADH, as can mechanical ventilation, pain, and certain malignancies.
Recent Guidelines and Recommendations
- The American Association for the Study of Liver Diseases recommends a serum sodium increase of up to 5 mmol/L in the first hour with a limit of 8–10 mmol/L every 24 hours thereafter until the serum sodium concentration reaches 130 mmol/L 1.
- The use of vasopressin receptor antagonists in cirrhosis can raise serum sodium during treatment, but they should be used with caution only for a short term (≤30 days) 1.
- Hypertonic sodium chloride administration may improve hyponatremia at the cost of worsening fluid overload, and is best reserved for those with severely symptomatic acute hyponatremia, especially if a transplant is imminent 1.
From the Research
Hyponatremia Workup in ICU Patients
- Hyponatremia is defined as serum sodium level <135 meq/L and is the most common electrolyte abnormality seen in hospital admissions worldwide, with an even higher proportion in the ICU setting 2.
- The most common cause of hyponatremia in ICU patients is SIADH (Syndrome of Inappropriate Antidiuretic Hormone Secretion) 2.
- Clinical manifestations of hyponatremia depend on its biochemical severity and duration, with symptoms being more pronounced with acute hyponatremia and less prominent in chronic hyponatremia 3.
Diagnostic Approach
- A physiological approach is recommended to determine if hyponatremia is hypotonic, if it is mediated by arginine vasopressin, and if arginine vasopressin secretion is physiologically appropriate 3.
- Serial serum electrolytes and urine sodium should be tested for all patients in the ICU satisfying the inclusion criteria 2.
Treatment and Correction
- The treatment of hyponatremia depends on the presence and severity of symptoms, with brain herniation being a concern when severe symptoms are present, and current guidelines recommending immediate treatment with hypertonic saline 3, 4.
- A 4 to 6 mEq/L increase in serum Na concentration is sufficient to treat life-threatening cerebral edema caused by acute hyponatremia, while in chronic hyponatremia, correction by > 8 to 10 mEq/L/d risks iatrogenic osmotic demyelination syndrome (ODS) 4.
- Patients with serum sodium correction have lower mortality and longer survival than patients without corrected serum sodium concentration 5.
Factors Influencing Outcome
- A lower Glasgow Coma Scale (GCS) and a lower serum sodium on admission are associated with lower survival 2.
- Under correction of hyponatremia in the first 24 hours or inadequate correction is associated with a poorer outcome, while overcorrection is not associated with any survival benefit but is associated with a risk of EPM (osmotic demyelination syndrome) 2.