How should I manage an elderly woman with severe dehydration and symptomatic hyponatraemia (serum sodium 105 mmol/L) presenting with confusion?

Management of Severe Symptomatic Hyponatremia with Dehydration

For an elderly woman with severe symptomatic hyponatremia (Na 105 mmol/L) presenting with confusion and clinical dehydration, immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over the first 6 hours or until confusion resolves, while simultaneously providing isotonic saline for volume repletion—but never exceed 8 mmol/L total correction in 24 hours to prevent osmotic demyelination syndrome. 1, 2

Immediate Emergency Management

Administer 3% hypertonic saline as 100 mL boluses over 10 minutes, repeating up to three times at 10-minute intervals until severe symptoms (confusion) begin to improve. 1 This approach targets a 6 mmol/L increase over 6 hours, which is sufficient to reverse hyponatremic encephalopathy without causing overcorrection. 1, 2

• Check serum sodium every 2 hours during the initial correction phase to ensure you stay within safe limits and avoid inadvertent overcorrection. 1, 3
• Once confusion resolves or 6 mmol/L correction is achieved, slow the rate dramatically to ensure the total 24-hour correction does not exceed 8 mmol/L. 1, 2

Volume Status Assessment and Concurrent Repletion

Assess for clinical signs of hypovolemia: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins, and tachycardia. 4, 1 In elderly patients with severe dehydration, these signs indicate true volume depletion requiring isotonic saline. 4

• Administer isotonic saline (0.9% NaCl) concurrently at 15-20 mL/kg/h initially, then 4-14 mL/kg/h based on clinical response to restore intravascular volume. 1, 5
• A urine sodium <30 mmol/L predicts good response to saline infusion with 71-100% positive predictive value, confirming hypovolemic hyponatremia. 1
• Monitor for signs of euvolemia: resolution of orthostatic hypotension, normal skin turgor, moist mucous membranes, and stable vital signs. 1

Critical Correction Rate Limits for Elderly Patients

The absolute maximum correction is 8 mmol/L in any 24-hour period for standard-risk patients. 1, 3, 2 However, elderly patients with severe baseline hyponatremia (Na 105 mmol/L) are at exceptionally high risk for osmotic demyelination syndrome. 1, 3

• For high-risk patients (elderly, malnourished, alcoholism, liver disease), limit correction to 4-6 mmol/L per day with an absolute maximum of 8 mmol/L in 24 hours. 1, 3
• The risk of osmotic demyelination syndrome is 0.5-1.5% even with careful correction in high-risk populations. 1
• Osmotic demyelination typically manifests 2-7 days after rapid correction with dysarthria, dysphagia, oculomotor dysfunction, and quadriparesis. 1, 3

Preventing Inadvertent Overcorrection

The most common cause of overcorrection is unexpected emergence of water diuresis once the underlying cause (often SIADH or volume depletion) resolves. 6 This is particularly dangerous in elderly patients.

• Consider concurrent desmopressin (1-2 µg parenterally every 6-8 hours) alongside hypertonic saline to prevent unpredictable water diuresis and maintain controlled correction. 6
• This combination allows predictable, controlled correction without exceeding safe limits and has been shown to prevent overcorrection in 100% of cases in one quality improvement study. 6
• Monitor urine output closely—large volumes of dilute urine signal risk of overcorrection. 3, 6

Management of Overcorrection (If It Occurs)

If sodium rises >8 mmol/L in 16-24 hours, immediately implement therapeutic relowering to prevent osmotic demyelination syndrome. 3, 7

• Administer D5W (5% dextrose in water) intravenously to actively relower sodium levels. 3, 7
• Give desmopressin (DDAVP) to prevent further urinary water losses and facilitate controlled relowering. 3, 7
• Target reduction of 2-4 mmol/L over 6-8 hours to bring total 24-hour correction to ≤8 mmol/L from baseline. 3
• Early relowering (within hours of overcorrection) can reverse disturbances in consciousness and prevent osmotic demyelination syndrome, as demonstrated in case reports. 7

Determining the Underlying Cause

While treating, rapidly assess the etiology to guide ongoing management after the acute phase. 1, 5, 2

• Hypovolemic hyponatremia (most likely in this dehydrated elderly patient): urine sodium <30 mmol/L, signs of volume depletion, elevated BUN/creatinine ratio >20:1. 1, 5
• Check serum and urine osmolality, urine sodium, and assess extracellular fluid volume status. 1, 2
• Review medications (diuretics, SSRIs, carbamazepine, NSAIDs) that commonly cause hyponatremia in elderly patients. 1, 2

Transition to Maintenance Phase

Once confusion resolves and sodium reaches 120-125 mmol/L, transition from hypertonic saline to isotonic maintenance fluids. 4, 1

• Continue isotonic saline at maintenance rates (30 mL/kg/day for adults) once clinical euvolemia is achieved. 1
• Avoid hypotonic fluids (0.45% saline, D5W, lactated Ringer's) which can worsen hyponatremia. 4, 1
• Monitor sodium every 4-6 hours after resolution of severe symptoms, then daily until stable. 1, 3

Common Pitfalls to Avoid

Never use fluid restriction as initial treatment for altered mental status from hyponatremia—this is a medical emergency requiring hypertonic saline. 1 Fluid restriction is appropriate only for euvolemic hyponatremia (SIADH) after symptoms resolve. 1, 2

Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours—overcorrection causes osmotic demyelination syndrome. 1, 3, 2 This is the single most important safety principle.

Never administer hypotonic fluids (lactated Ringer's, 0.45% saline) to patients with hyponatremia, as they worsen the sodium deficit. 4, 1 Use only isotonic or hypertonic solutions.

Never delay treatment while pursuing a complete diagnostic workup—treat severe symptomatic hyponatremia immediately. 5, 2 The diagnosis can be refined during treatment.