How to manage a patient with Subdural Hematoma (SDH) and hyponatremia?

Management of Subdural Hematoma with Hyponatremia

Critical Initial Assessment

In a patient with subdural hematoma (SDH) and hyponatremia, you must immediately distinguish between SIADH and cerebral salt wasting (CSW), as these require fundamentally opposite treatment approaches—this distinction is life-saving. 1, 2

Volume Status Determination

• Assess extracellular fluid volume status through physical examination: look for orthostatic hypotension, dry mucous membranes, decreased skin turgor (suggesting CSW/hypovolemia) versus normal volume status (suggesting SIADH) 1, 2
• Check for evidence of volume depletion: confusion, non-fluent speech, extremity weakness, dry tongue, furrowed tongue, sunken eyes, decreased venous filling, and postural pulse changes 1
• CSW presents with hypovolemia (hypotension, tachycardia, dry mucous membranes) while SIADH is euvolemic (no edema, no orthostatic hypotension, normal skin turgor, moist mucous membranes) 1, 2

Laboratory Workup

• Obtain serum sodium, serum osmolality (<275 mOsm/kg suggests true hyponatremia), urine osmolality (>100 mOsm/kg in SIADH), and urine sodium (>20 mEq/L in both SIADH and CSW) 1, 2
• Serum uric acid <4 mg/dL has 73-100% positive predictive value for SIADH 1, 3
• Check thyroid function and cortisol to rule out hypothyroidism and adrenal insufficiency 1
• Urine sodium >20 mEq/L with high urine osmolality (>500 mOsm/kg) suggests SIADH, while urine sodium >20 mEq/L with evidence of volume depletion suggests CSW 1, 2

Treatment Algorithm Based on Severity and Etiology

Severe Symptomatic Hyponatremia (Seizures, Coma, Altered Mental Status)

For severe symptoms regardless of etiology, immediately administer 3% hypertonic saline with goal to correct 6 mmol/L over 6 hours or until severe symptoms resolve. 1, 3, 2

• Give 3% hypertonic saline as 100 mL boluses over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve 1
• Total correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 3, 2
• Transfer to ICU for close monitoring with serum sodium checks every 2 hours initially 1, 3, 2
• After severe symptoms resolve, monitor serum sodium every 4 hours 1

Treatment of SIADH in Neurosurgical Patients

For mild/asymptomatic SIADH, fluid restriction to 1 L/day is the cornerstone of treatment. 1, 3, 2

• Implement strict fluid restriction to 1000 mL/day 1, 3, 2
• If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1
• Consider demeclocycline as second-line treatment for chronic SIADH when fluid restriction is ineffective 3
• Never use fluid restriction in patients with subarachnoid hemorrhage at risk for vasospasm, as this worsens outcomes 1, 3, 2

Treatment of Cerebral Salt Wasting (CSW)

CSW requires aggressive volume and sodium replacement—fluid restriction will worsen outcomes and is contraindicated. 1, 2

• Administer isotonic (0.9%) saline for volume repletion in mild cases 1, 2
• For severe symptoms or profound hypovolemia, use 3% hypertonic saline with careful monitoring 1, 2
• Add fludrocortisone 0.1-0.2 mg daily for CSW, particularly in subarachnoid hemorrhage patients at risk for vasospasm 1, 2
• Consider hydrocortisone to prevent natriuresis in subarachnoid hemorrhage patients 1, 2
• Aggressive volume resuscitation with crystalloid or colloid agents ameliorates the risk of cerebral ischemia 2

Moderate Hyponatremia (Sodium 120-125 mmol/L)

• For SIADH: fluid restriction to 1-1.5 L/day 1, 3
• For CSW: continue volume and sodium replacement with isotonic saline 1, 2
• Monitor serum sodium every 4-6 hours during active correction 1

Mild Hyponatremia (Sodium 126-135 mmol/L)

• Do not ignore mild hyponatremia—it increases fall risk (21% vs 5%) and mortality (60-fold increase when <130 mmol/L) 1
• For SIADH: fluid restriction and close monitoring 1, 3
• For CSW: maintain adequate volume status with normal saline 1, 2
• A sodium level of 131 mmol/L or lower merits evaluation and treatment in neurosurgical patients 2

Correction Rate Guidelines and Prevention of Osmotic Demyelination

The maximum correction rate is 8 mmol/L in 24 hours for all patients; slower rates (4-6 mmol/L per day) are required for high-risk patients. 1, 2

High-Risk Patients Requiring Slower Correction (4-6 mmol/L per day)

• Advanced liver disease 1, 4
• Alcoholism or alcohol use disorder 1, 4
• Malnutrition 1, 4
• Severe hyponatremia with initial sodium <115 mEq/L 4
• Hypokalemia 4

Managing Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours, immediately intervene to prevent osmotic demyelination syndrome. 1

• Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1
• Administer desmopressin 1-2 µg parenterally to slow or reverse the rapid rise 1, 5, 6
• Target reduction to bring total 24-hour correction to no more than 8 mmol/L from starting point 1
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1

Proactive Strategy to Prevent Overcorrection

Consider concurrent desmopressin (1-2 µg parenterally every 6-8 hours) with hypertonic saline in severe hyponatremia to prevent inadvertent overcorrection from spontaneous water diuresis. 5, 6

• This proactive strategy is associated with lower incidence of exceeding correction targets 5, 6
• Allows predictable, controlled correction without risk of sudden water diuresis 6
• Mean correction rates with this approach are 5.8 ± 2.8 mEq/L in first 24 hours without exceeding 12 mEq/L 6

Critical Pitfalls to Avoid

• Using fluid restriction in CSW instead of SIADH—this is the most dangerous error and worsens outcomes 1, 2
• Correcting chronic hyponatremia too rapidly (>8 mmol/L in 24 hours), especially in patients with sodium <115 mEq/L 1, 4
• Failing to distinguish between SIADH and CSW based on volume status 1, 2
• Inadequate monitoring during active correction 1
• Using fluid restriction in subarachnoid hemorrhage patients at risk for vasospasm 1, 3, 2
• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant 1

Special Considerations for SDH Patients

• Hyponatremia itself contributes to neurological impairment and is not just a biomarker of illness severity 2
• A sodium level of 120 mmol/L is the critical threshold for development of seizures 2
• Hyponatremia in neurosurgical patients with subarachnoid hemorrhage is associated with higher rates of cerebral ischemia and worse outcomes at 3 months 3
• Even mild hyponatremia requires closer monitoring in neurosurgical patients as it may indicate underlying CSW or SIADH 1