Hyponatremia management

Definition

Hyponatremia is defined as a serum sodium (Na⁺) concentration of <135 mEq/L.

It is classified as:

• Mild: 130–135 mEq/L

• Moderate: 125–129 mEq/L

• Severe: <125 mEq/L

Clinical presentation

Clinical manifestations usually occur when the serum sodium concentration is <125 mEq/L.

Patients may present with:

• Nausea and vomiting

• Fatigue

• Dizziness

• Headache

• Confusion

• Tremulousness

• Seizures

• Loss of consciousness or coma

• Muscle cramps or spasms

• Irritability

• Restlessness

• Weakness

• Thirst

• Anorexia

Investigations

Investigations should be guided by the severity of hyponatremia and the patient's clinical findings.

Recommended investigations include:

• Point-of-care random blood glucose (RBG)

• Urine dipstick

• Serum electrolytes

• Serum creatinine and urea

• Liver function tests (LFTs)

• Serum osmolality

• Urine sodium (Na⁺)

• Urine osmolality

• Thyroid function profile

• CT scan of the brain (if a cerebral process is suspected)

• Chest X-ray (if pulmonary infection, pulmonary edema, renal failure, or congestive cardiac failure is suspected)

Non-pharmacological treatment

Provide nutritional measures according to the patient's needs, including:

• Salt-containing foods

• Rehydration therapy

• Dietary modification

The goals of acute management are:

• Treat serious complications.

• Restore serum sodium carefully.

• Identify and treat the underlying cause.

Management depends on:

• Cause

• Severity

• Duration of hyponatremia

Based on duration, hyponatremia is classified as:

• Acute

• Chronic

Pharmacological treatment

Acute hyponatremia

Typically symptomatic with onset <48 hours.

Common manifestations include:

• Neurological deficits

• Seizures

• Coma

• Confusion

Management

Requires immediate treatment.

3% Sodium chloride (IV)

• Infuse at 1–2 mEq/L/hour.

Alternative

Sodium bicarbonate 8.4% (IV)

• 50 mL over 5 minutes.

Important precautions

• Do not increase serum sodium by more than 6 mmol/L within 6 hours.

• Stop the infusion once symptoms have resolved.

• Manage seizures and coma appropriately.

Chronic hyponatremia

Usually asymptomatic with onset >48 hours.

Mild, asymptomatic hyponatremia

• No specific treatment is required.

Moderate to severe hyponatremia

0.9% Sodium chloride (IV)

Important precautions

• Do not increase serum sodium by more than 12 mmol/L during the first 24 hours.

• Stop correction once serum sodium reaches 130 mEq/L or symptoms have resolved.

Assessment of volume status

Assess volume status using:

• Point-of-care ultrasound (POCUS) assessment of the inferior vena cava (IVC)

• Vital signs

Classify the patient as having:

• Hypovolemic hyponatremia

• Euvolemic hyponatremia

• Hypervolemic hyponatremia

Management according to volume status

Hypovolemic hyponatremia

Possible causes

• Dehydration

• Vomiting

• Diarrhea

• Excessive sweating

• Third spacing

• Hydration with hyperosmolar fluids

Treatment

Compound sodium lactate (IV)

OR

0.9% Sodium chloride (IV)

• 250–500 mL, or

• 0.5–1 mL/kg/hour

Adjust the infusion rate according to the patient's blood pressure response.

Euvolemic hyponatremia

Possible causes

• Psychogenic polydipsia

• Iatrogenic causes

• Syndrome of inappropriate antidiuretic hormone secretion (SIADH)

• MDMA (ecstasy) use

• Hypothyroidism

• Pseudohyponatremia

Management

• Prevent further worsening of hyponatremia.

• Prevent rapid overcorrection.

• Insert a Foley catheter to monitor urine output.

Hypervolemic hyponatremia

Possible causes

• Renal failure

• Cirrhosis

• Nephrotic syndrome

• Congestive cardiac failure

Treatment

• Keep the patient nil per oral (NPO).

• Restrict fluids.

Furosemide (IV)

• 40 mg daily until fluid overload has resolved.

Severe hyponatremia

Patients with seizures, coma, or signs of brainstem herniation should be managed as having cerebral edema and raised intracranial pressure.

Treatment

3% Sodium chloride (IV)

• 3–5 mL/kg over 15–60 minutes.

• Target an increase in serum sodium of 2–4 mmol/L.

Monitoring

• Monitor serum sodium hourly initially.

• Target a correction rate of:

  • No more than 8–10 mmol/L/day

  • Less than 0.5 mmol/L/hour over the first 1–2 hours

Hypovolemic hyponatremia: sodium deficit calculation

Determine the sodium deficit using:

Total body sodium deficit = (Desired serum sodium − Actual serum sodium) × Total body water

Where:

• Men: Total body water = 0.6 × body weight (kg)

• Women: Total body water = 0.5 × body weight (kg)

Replacement

0.9% Sodium chloride (IV)

Correct serum sodium at a rate of no more than 0.5 mmol/L/hour.

Important notes

• Monitor for complications of overcorrection, including osmotic demyelination syndrome (ODS).

• Hyponatremia may cause cerebral edema, leading to increased intracranial pressure (ICP).

• Exercise-associated hyponatremia commonly results from overhydration rather than excessive water loss.

• Psychogenic polydipsia results from excessive water intake, particularly in patients with psychiatric illness or those receiving selective serotonin reuptake inhibitors (SSRIs).

Disposition

Patients with:

• Symptomatic hyponatremia

• Severe hyponatremia

should be admitted to a High Dependency Unit (HDU) or Intensive Care Unit (ICU) for continuous biochemical and clinical monitoring.

If these services are unavailable, refer the patient to a higher-level facility with HDU or ICU capability.