Can mannitol be abruptly discontinued if serum sodium reaches hypernatremia?

Mannitol Discontinuation with Hypernatremia

No, mannitol should not be abruptly discontinued when serum sodium reaches 150 mEq/L. Instead, mannitol should be held when serum osmolality reaches ≥320 mOsm/kg or when serum sodium exceeds 155 mEq/L, not at 150 mEq/L 1.

Monitoring Parameters and Discontinuation Thresholds

The critical threshold for mannitol discontinuation is serum osmolality ≥320 mOsm/kg, not serum sodium alone 1, 2. The guideline for managing cerebral edema with mannitol specifically states to check metabolic profile and serum osmolality every 6 hours, and hold mannitol if serum osmolality is ≥320 mOsm/kg or osmolality gap is ≥40 1.

Specific Monitoring Protocol

• Check serum osmolality and metabolic profile every 6 hours during mannitol therapy 1
• Hold mannitol if serum osmolality ≥320 mOsm/kg 1, 2
• Hold mannitol if osmolality gap ≥40 1
• For hypertonic saline protocols, hold infusion only if sodium >155 mEq/L 1

Why Sodium 150 mEq/L is Not the Discontinuation Point

A serum sodium of 150 mEq/L is actually within the therapeutic target range when managing cerebral edema 1. The guideline explicitly recommends targeting serum sodium levels of 150-155 mEq/L when using hypertonic saline for cerebral edema management 1. This indicates that sodium levels up to 155 mEq/L are considered acceptable and therapeutic in this clinical context.

Research demonstrates that severe hypernatremia (>160 mEq/L), not mild hypernatremia (150 mEq/L), is independently associated with increased mortality in neurologic intensive care patients 3. Hypernatremia is common in patients treated with mannitol (24.3% incidence), and only severe elevations pose independent mortality risk 3.

Clinical Decision Algorithm

At sodium 150 mEq/L:

1. Continue mannitol therapy 1
2. Check serum osmolality immediately 1, 2
3. If osmolality <320 mOsm/kg → continue mannitol with 6-hourly monitoring 1
4. If osmolality ≥320 mOsm/kg → hold mannitol 1, 2

At sodium >155 mEq/L:

1. Hold mannitol regardless of osmolality 1
2. Perform daily CT of head 1
3. Adjust medications to prevent rebound cerebral edema 1

Common Pitfalls to Avoid

Do not use serum sodium alone as the discontinuation criterion - serum osmolality is the primary parameter 1, 2. Studies show that 33% of patients receiving standard mannitol protocols develop serum osmolality ≥320 mOsm/kg, indicating the need for osmolality-guided rather than sodium-guided therapy 2.

Do not abruptly stop mannitol without considering rebound cerebral edema risk 1. The guideline emphasizes adjusting medications to prevent rebound cerebral edema, renal failure, electrolyte abnormalities, hypovolemia, and hypotension 1.

Mannitol therapy should be guided by 12-hourly measurement of serum osmolality when used beyond 48 hours 2. If osmolality monitoring is unavailable, mannitol should be limited to 48 hours only 2.