Hypernatremia

What is Hypernatremia?

Hypernatremia is a medical condition in which the concentration of sodium (Na⁺) in the blood is higher than normal. Normal serum sodium levels range from 135–145 milliequivalents per liter (mEq/L). Hypernatremia is generally defined as a serum sodium level ≥ 146 mEq/L. Because sodium is the primary extracellular cation, an excess pulls water out of cells, leading to cellular dehydration and a cascade of neurologic and systemic effects.

Most cases develop gradually over hours to days, but rapid rises (≥ 0.5 mEq/L per hour) can cause severe brain injury. The condition is more common in infants, older adults, and people who cannot adequately express thirst or access water.

Common Causes

Hypernatremia usually results from a relative loss of free water rather than an actual excess of sodium. Below are the most frequent contributors, grouped by mechanism.

• Dehydration due to inadequate fluid intake – especially in infants, the elderly, or patients with impaired thirst.
• Excessive water loss via the kidneys – diuretics (especially loop diuretics), osmotic diuresis from uncontrolled diabetes mellitus, or hyperglycemia.
• Gastrointestinal losses – profuse vomiting, diarrhea, or nasogastric suction that removes water‑rich fluids.
• Insensible losses – high fever, extensive burns, or severe hyperventilation that increase evaporative water loss.
• Hypertonic saline or sodium‑rich medication administration – IV hypertonic saline, sodium bicarbonate, or certain contrast agents.
• Primary adrenal insufficiency (Addison’s disease) – loss of aldosterone leads to sodium wasting, but paradoxically, low cortisol can cause a relative water deficit.
• Diabetes insipidus (central or nephrogenic) – deficiency of antidiuretic hormone (ADH) or renal resistance to ADH causes large volumes of dilute urine.
• Cerebral salt‑wasting syndrome – a rare complication of brain injury that leads to natriuresis and water loss.
• Hyperglycemia with osmotic diuresis – elevated glucose pulls water into the extracellular space, then excreted, concentrating sodium.
• Excessive intake of salt‑laden foods or supplements – usually only a factor when combined with inadequate water intake.

Associated Symptoms

The clinical picture depends on how quickly sodium rises and the total body water deficit. Common manifestations include:

• Thirst (often intense)
• Dry mouth, cracked lips, and dry mucous membranes
• Decreased skin turgor, sunken eyes, or fontanelle in infants
• Weakness, fatigue, or lethargy
• Neurologic signs – irritability, confusion, agitation, seizures, or coma (especially with rapid onset)
• Muscle twitching or cramps
• Hyperreflexia and positive Babinski sign in severe cases
• Elevated heart rate and low blood pressure secondary to volume depletion

When to See a Doctor

Because hypernatremia can progress silently, it is important to seek medical attention promptly if you notice any of the following:

• Persistent or worsening thirst that does not improve with normal fluid intake.
• Signs of dehydration – dry mouth, scant urine, dizziness, or fainting.
• Neurologic changes such as confusion, disorientation, seizures, or sudden weakness.
• Infants with a bulging or sunken fontanel, high‑pitched crying, or failure to feed.
• Older adults who become unusually quiet, confused, or develop falls.
• Any patient receiving hypertonic saline, high‑dose diuretics, or with a known disorder of water balance who feels “off.”

Diagnosis

The work‑up for hypernatremia aims to confirm the serum sodium level, assess severity, and uncover the underlying cause.

Laboratory Tests

• Serum electrolytes – sodium, potassium, chloride, bicarbonate.
• Serum osmolality – usually > 300 mOsm/kg in hypernatremia.
• Urine sodium and osmolality – helps differentiate renal loss (e.g., diabetes insipidus) from extrarenal loss.
• Blood glucose, BUN, creatinine – evaluate for hyperglycemia, renal function, and volume status.
• Hormone assays (if indicated) – ADH (vasopressin), cortisol, aldosterone.

Clinical Assessment

• Physical examination for volume status (skin turgor, mucous membranes, orthostatic vitals).
• Neurologic exam – mental status, reflexes, pupil size.
• Review of fluid intake/output records, medication list, and recent illnesses.

Imaging (when needed)

• CT or MRI of the brain if neurologic deficits are unexplained, to rule out intracranial hemorrhage or stroke.
• Chest X‑ray may be ordered if pulmonary edema or infection is suspected.

Treatment Options

Treatment focuses on safely lowering serum sodium while correcting the underlying cause. Rapid correction can cause cerebral edema, so the rate of change is crucial.

General Principles

• Identify whether hypernatremia is acute (< 48 h) or chronic (> 48 h). Acute cases may be corrected slightly faster (0.5–1 mEq/L per hour) under close monitoring.
• Target a reduction of 0.5 mEq/L per hour** or **no more than 10–12 mEq/L in the first 24 hours** for chronic cases.
• Replace free water, not sodium, unless the patient is also volume‑depleted.