What is the best fluid management strategy for a patient with brain injury and hypernatremia?

Fluid Management for Brain Injury with Hypernatremia

In brain injury patients with hypernatremia, discontinue or reduce hypertonic saline infusions when sodium exceeds 155 mmol/L, switch to 0.9% normal saline for maintenance fluids, and avoid prolonged hypernatremia as it does not improve outcomes and increases complications. 1, 2, 3

Understanding the Clinical Context

Hypernatremia in brain injury typically results from therapeutic hypertonic saline administration for intracranial pressure (ICP) control, not from the injury itself. 3 The key issue is that while hypertonic saline effectively reduces ICP acutely (lasting only 2-4 hours after bolus), prolonged hypernatremia provides no additional benefit and increases risk of serious complications. 1, 3

The 2018 guidelines for severe traumatic brain injury explicitly recommend against using prolonged hypernatremia to control intracranial pressure (Grade 2-, Strong Agreement). 1 This recommendation is based on several critical limitations:

• The relationship between serum sodium and ICP is weak 1
• Theoretical benefits require an intact blood-brain barrier, which is often disrupted in brain injury 1
• Rapid brain cell volume regulation limits effectiveness of prolonged hyperosmolarity, creating risk of "rebound" ICP during correction 1
• Hypernatremia-associated hyperchloremia may impair renal function 1

Immediate Management Steps

Stop or reduce hypertonic saline when sodium >155 mmol/L: 2, 3

• The therapeutic target range is 145-155 mmol/L 3
• Upper safety limit is 155-160 mmol/L 3
• Sodium >170 mEq/L sustained for >72 hours significantly increases risk of thrombocytopenia, renal failure, neutropenia, and acute respiratory distress syndrome 3

Switch to 0.9% normal saline for maintenance fluids: 1, 2, 4

• This is the only commonly available isotonic crystalloid appropriate for brain injury (Strong recommendation, moderate quality evidence) 1
• Normal saline maintains plasma osmolality without increasing brain water 4, 5
• Avoid hypotonic solutions (Ringer's lactate, Ringer's acetate) as they are hypotonic when real osmolality is measured and will increase brain water (Strong recommendation, moderate quality evidence) 1, 4

Monitoring During Correction Phase

Monitor the following parameters closely: 3

• Serum sodium every 4-6 hours 3
• Serum osmolality daily 3
• Neurological examinations every 2-4 hours 3
• ICP if catheter is in place 3

Critical pitfall: The FDA label for mannitol warns that "with continued administration of mannitol, loss of water in excess of electrolytes can cause hypernatremia," and emphasizes that "electrolyte measurements, including sodium and potassium are therefore of vital importance in monitoring the infusion of mannitol." 6

Alternative ICP Management if Needed

If acute ICP elevation occurs during sodium correction: 3

• Consider mannitol 0.25-1 g/kg IV bolus over 15-20 minutes 3
• Elevate head of bed 20-30 degrees to assist venous drainage 3
• Do not use mannitol and hypertonic saline simultaneously 3
• Do not re-administer hypertonic saline boluses until sodium is <155 mmol/L 3

Evidence Limitations

Despite hypertonic saline's effectiveness in reducing ICP, there is no evidence it improves neurological outcomes (Grade B) or survival (Grade A) in patients with raised intracranial pressure. 3 A 2016 retrospective study of 231 severe TBI patients found that neither hypertonic saline nor hypernatremia was associated with hospital mortality, though patients receiving hypertonic saline did observe significant ICP reduction. 7 However, this does not justify prolonged hypernatremia beyond the acute ICP crisis.

Avoid These Common Errors

• Never use albumin in traumatic brain injury patients (Strong recommendation, moderate quality evidence) as it increases mortality 1, 2
• Never restrict fluids excessively as this may cause hypotension, which worsens ICP and neurologic outcome 5
• Never use hypotonic solutions (5% dextrose in water, Ringer's lactate) as they reduce serum sodium, increase brain water, and increase ICP 5
• Never pursue permissive hypotension in brain injury as adequate cerebral perfusion pressure is crucial 4