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Hypernatremia

Lauren Chan

Overview of dysnatremias

  • Fluctuations in serum Na reflect fluctuations in plasma free water

  • Sodium is the major driver of tonicity. The clinical signs and symptoms of serum Na fluctuations are related to changes in tonicity with most profound effects on cerebral tissue

  • Two major mechanisms maintain plasma osmolarity between 275 and 290: Thirst and secretion of ADH. When these mechanisms malfunction, dysnatremias occur

Background

  • Definition: Na+ >145

  • Hypernatremia = decreased free water

  • Almost always due to inadequate free water intake (ICU patients, dementia, limited mobility, tube feeding/TPN, impaired thirst/adipsia from hypothalamic stroke). Hospital acquired hypernatremia is iatrogenic and correlates with poor outcomes

  • Can also occur from: Na+ overload (salt poisoning, iatrogenic from NS infusion, over correction), osmotic diuresis (hyperglycemia, SGLT-2 inhibitors, urea, mannitol), diabetes insipidus

Presentation

  • Lethargy, irritability, confusion

  • Seizures, coma, hemorrhagic stroke, or subarachnoid hemorrhage (from the effects of hypertonic serum on cerebral vasculature)

Evaluation

  • Step 1: Treat underlying cause (vomiting, hyperglycemia, medications)

  • Step 2: Determine volume status: If severely hypovolemic, the patient will need IV crystalloid to restore volume in addition to free water

  • Step 3: Estimate and replace free water deficit (FWD):

    • FWD = TBW x [(serum Na/140) - 1]

  • Step 4: Account for ongoing insensible losses and electrolyte free water clearance

    • Rule of thumb for accounting for electrolyte free water clearance. This is in addition to replacing free water deficit

      • 0-1 Liter of urine output: Ignore, no need to replace

      • 1-3 Liters of urine output: Replace half of the losses

      • >3 liters of urine output: Replace all urine losses

  • No evidence that overcorrecting hypernatremia is harmful. In fact, there is increased mortality with overly cautious correction or under correction

  • If able, replace free water enterally. Otherwise, administer D5W intravenously

Additional Information

  • Pts w/ suspected DI: Consult Nephrology (may require desmopressin or may receive desmopressin once stabilized to differentiate between central and nephrogenic DI)

  • Pts with hypokalemia: giving K decreases total amount of free water you are giving the pt