Hypernatremia

Hypernatremia

Anesthetic relevance	Moderate
Anesthetic management	If severe, delay elective surgery Correct slowly (≤0.5 mEq/hr)
Specialty	Nephrology, neurology
Signs and symptoms	Depending on severity: Restlessness Irritability Ataxia Hyperreflexia Seizure Coma Death May also have symptoms related to the underlying cause of hypernatremia (e.g. thirst, vomiting, diarrhea, polyuria)
Diagnosis	Serum sodium Serum osmolality, urine sodium and osmolality (to determine etiology)
Treatment	Replace free water deficit Correct slowly (≤0.5 mEq/hr)
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Chris Rishel

Hypernatremia is an abnormally high concentration of sodium in the blood, and can occur on an acute or chronic basis. Hypernatremia leads to a hyperosmolar state, and serum osmolarity often correlates with patient symptoms. Hypernatremia may also be intentionally induced to manage ICP.

Anesthetic implications

Preoperative optimization

• Consider postponing elective cases until treated/stable
• Perform focused neuro exam

Intraoperative management

• Frequent sodium rechecks to ensure appropriate correction rate

Related surgical procedures

• Hypernatremia may be intentionally induced to manage critical ICP before performing a craniotomy

Pathophysiology

• Underlying pathophysiology varies depending on etiology (see Diagnosis section), but typically relates to a total body free water deficit
• If severe/acute can lead to
  • Brain shrinkage and myelinolysis
  • Traction of cerebral vessels, which can cause
    • Hemorrhage
    • Venous sinus thrombosis
    • Infarction

Signs and symptoms

Serum osmolality	Symptoms
350-375	Restlessness, irritability
376-400	Tremulousness, ataxia
400-430	Hyperreflexia, twitching, spasticity
>430	Seizure, coma, death

Diagnosis

• Differential diagnosis guided by comparison of serum and urine osmolality
• If urine osmolality appropriate (700-800 mOsm/kg), differential includes:
  • Water loss
    • Vomiting
    • Diarrhea
    • Sweating
  • Sodium overload
    • Increased sodium intake
    • Sodium bicarbonate administration
    • Renal sodium retention
  • Lack of thirst (rare)
• If urine osmolality low (<300 mOsm/kg), consider diabetes insipidus:
  • Central diabetes insipidus (desmopressin challenge/therapy improves urine concentration)
    • Head trauma
    • CVA
    • Tumor
  • Nephrogenic diabetes insipidus

Treatment

• If water loss or sodium overload, replace free water deficit
  • Typically use 1/2 NS
  • Correct slowly (≤0.5 mEq/hr)
  • Frequently recheck sodium to ensure correction rate
  • If corrected too quickly, risk of cerebral edema
• If central DI, treat with desmopressin

Free water deficit