What is the plan of care for a patient with cerebral salt wasting, presenting with hypovolemia and hyponatremia, and impaired renal function?

Plan of Care for Cerebral Salt Wasting

Immediate Recognition and Diagnosis

Cerebral salt wasting (CSW) is a hypovolemic hyponatremia requiring aggressive volume and sodium replacement—the opposite approach from SIADH—and fluid restriction will worsen outcomes and potentially precipitate cerebral ischemia. 1, 2

The diagnosis requires:

• Hyponatremia with evidence of extracellular volume depletion (orthostatic hypotension, tachycardia, dry mucous membranes, flat neck veins, prolonged capillary refill) 1, 3
• Inappropriately high urinary sodium concentration (typically >20 mmol/L despite volume depletion) 4, 1, 5
• High urine osmolality relative to serum osmolality 1
• Central venous pressure <6 cm H₂O (versus 6-10 cm H₂O in SIADH) 4, 1

CSW is more common in patients with poor clinical grade, ruptured anterior communicating artery aneurysms, hydrocephalus, and severe traumatic brain injury 1, 6.

Initial Fluid and Sodium Replacement

Begin with isotonic saline (0.9% NaCl) at 15-20 mL/kg/h for initial volume resuscitation to restore intravascular volume and correct hypovolemia 4, 2. Subsequent infusion rates should be 4-14 mL/kg/h based on clinical response and corrected serum sodium 4.

For severe symptomatic hyponatremia (seizures, altered mental status, coma) or sodium <120 mmol/L:

• Administer 3% hypertonic saline immediately with initial goal to correct 6 mmol/L over 6 hours or until severe symptoms resolve 4, 1, 2
• Substantial volumes of hypertonic saline may be required for prolonged periods to correct volume and sodium deficits 7, 6
• Aggressive volume resuscitation with crystalloid or colloid agents can reduce the risk of cerebral ischemia, particularly critical in subarachnoid hemorrhage patients 1, 2

Critical Correction Rate Limits

Total sodium correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 4, 1, 2. This is the single most important safety parameter. Monitor serum sodium every 2 hours initially during active correction, then every 4 hours after severe symptoms resolve 4, 2.

Fludrocortisone as Essential Adjunctive Therapy

Fludrocortisone should be strongly considered as adjunctive therapy, especially when sodium losses persist despite aggressive saline replacement 1, 2, 7. The typical dosing is:

• Initial dose: 0.1-0.2 mg daily 4, 1
• May be increased to 50-150 μg/day based on response 6
• Fludrocortisone likely reduces the doses of hypertonic saline required and helps maintain serum sodium levels 7, 6

Alternatively, hydrocortisone may be used to prevent natriuresis in subarachnoid hemorrhage patients, though fludrocortisone is more commonly studied 4, 1, 2.

Special Considerations for Subarachnoid Hemorrhage

Hyponatremia in subarachnoid hemorrhage patients at risk of vasospasm should NEVER be treated with fluid restriction 4, 1, 2. Maintenance of normovolemia or slight hypervolemia is required to prevent vasospasm-related cerebral ischemia 2. Hypertonic saline increases regional cerebral blood flow, brain tissue oxygen, and pH in high-grade subarachnoid hemorrhage 1. Fludrocortisone may be considered specifically to prevent vasospasm in this population 4, 1, 2.

Monitoring Requirements

Track the following parameters:

• Serum sodium every 2 hours initially, then every 4 hours after symptom resolution 4, 2
• Daily weights and fluid balance to assess volume status 2
• Urine output and urine sodium concentration to gauge ongoing renal losses 2, 5
• Renal function and electrolytes (potassium, magnesium, phosphate) once or twice daily 8
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 4, 2

Management of Impaired Renal Function

In patients with elevated creatinine and impaired renal function:

• Provide volume expansion with isotonic saline or 20% albumin for volume repletion 4
• Limit sodium correction to 4-6 mmol/L per day (maximum 8 mmol/L in 24 hours) due to higher risk of osmotic demyelination syndrome 4
• Avoid hypertonic saline unless severe neurological symptoms are present 4
• Consider continuous venovenous hemofiltration (CVVH) with low-sodium replacement fluid for controlled sodium correction if urgent dialysis is required 4

Common Pitfalls to Avoid

• Using fluid restriction in CSW worsens outcomes and can precipitate cerebral ischemia—this is the most critical error 4, 1, 2
• Failing to distinguish CSW from SIADH leads to inappropriate treatment with potentially catastrophic consequences 1, 2, 5
• Inadequate monitoring during active correction can result in overcorrection and osmotic demyelination syndrome 4, 1, 2
• Correcting sodium too rapidly (>8 mmol/L in 24 hours) risks osmotic demyelination syndrome 4, 1, 2
• Misdiagnosing volume status in patients with CSW can lead to inappropriate fluid restriction 4