What are the risks of dialysis in a Neurological Intensive Care Unit (Neuro ICU) setting?

Dangers of Dialysis in the Neuro ICU

Dialysis in neurocritical care patients carries significant risk of intracranial pressure elevation and neurological deterioration, with continuous renal replacement therapy (CRRT) strongly preferred over intermittent hemodialysis to minimize these complications. 1

Primary Neurological Risks

Intracranial Pressure Elevation

• Hemodialysis increases ICP from baseline median of 11.9 mm Hg to peak of 21 mm Hg during treatment, representing a clinically significant rise that can worsen outcomes 2
• The ICP elevation correlates positively with baseline plasma urea concentration (Spearman's r = 0.69), meaning higher pre-dialysis urea levels predict greater ICP surges 2
• Intermittent hemodialysis (IHD) causes faster ICP peaks (75 minutes) compared to CRRT (375 minutes), making IHD particularly dangerous in acute settings 2
• Dialysis disequilibrium syndrome can cause severe intracranial hypertension requiring treatment cessation, increased sedation, and hypertonic saline rescue 3

Cerebral Edema Worsening

• Osmotic fluid shifts across the blood-brain barrier during dialysis can exacerbate cerebral edema in patients with acute brain injury 1, 4
• Patients with existing cerebral edema or at risk for it (traumatic brain injury, intracerebral hemorrhage, large strokes) are particularly vulnerable 1
• Rapid solute removal creates osmotic gradients that draw fluid into brain tissue 5, 4

Hemodynamic Complications

Cerebral Perfusion Compromise

• Excessive ultrafiltration reduces systemic arterial blood pressure, which decreases cerebral perfusion pressure and can extend ischemic injury 1
• Large hemodynamic shifts during IHD compromise cerebral perfusion more than CRRT 4
• Hypotension from dialysis is particularly dangerous in patients with impaired cerebral autoregulation following acute brain injury 1

Cardiovascular Instability

• Older adults and hemodynamically unstable patients are at highest risk, with CRRT required over IHD in cardiogenic shock scenarios 1
• Rapid volume changes provoke cardiovascular instability that translates to intracranial instability 4

Hemorrhagic Risks

Anticoagulation Complications

• Systemic anticoagulation required for CRRT may provoke intracerebral hemorrhage at injury sites or around ICP monitoring devices 4
• This creates a therapeutic dilemma in patients with traumatic brain injury or hemorrhagic stroke who require both dialysis and anticoagulation 4
• Regional citrate anticoagulation with hypertonic citrate solutions adds additional osmotic considerations 5

Modality-Specific Dangers

Intermittent Hemodialysis Risks

• IHD should be avoided in patients with or at risk for cerebral edema (Grade C recommendation) 1
• When IHD is unavoidable, it frequently requires pauses or early cessation due to ICP elevations 3
• Faster solute clearance with IHD creates steeper osmotic gradients across the blood-brain barrier 2

CRRT Considerations

• While CRRT is safer than IHD, exacerbations of cerebral edema have still been reported 6
• CRRT requires continuous anticoagulation, increasing hemorrhage risk over extended periods 4
• Despite risks, CRRT is recommended over IHD for ARF patients with or at risk for cerebral edema (Grade C) 1

Risk Mitigation Strategies

Dialysis Prescription Modifications

• Consider delaying dialysis if patient is particularly at risk of raised ICP 1
• Use cooled dialysate to minimize metabolic stress 1
• Avoid dialyzers with large surface areas to reduce rapid solute shifts 1
• Start blood flow slowly and increase gradually 1
• Perform gentle fluid removal, as excessive ultrafiltration reduces cerebral perfusion 1

When IHD is Necessary

• Use small dialyzers with low blood and dialysate flow rates 3
• Employ high dialysate sodium content to minimize osmotic gradients 3
• Consider separating ultrafiltration from hemodialysis, as isolated ultrafiltration is better tolerated 3
• Continuous ICP monitoring should be considered during hemodialysis in at-risk patients 3

Therapeutic Hypernatremia Protocol

• Maintain controlled hypernatremia of approximately 155 mEq/L using hypertonic saline (3% NaCl) during CRRT to minimize osmotic gradients across the blood-brain barrier 5
• This approach prevents ICP worsening by maintaining plasma hypertonicity 5
• For combined metabolic and respiratory acidosis, consider 4.2% sodium bicarbonate instead 5

High-Risk Patient Populations

Specific Conditions Requiring Extra Caution

• Large cerebral infarcts with high-grade stenosis 1
• Intracerebral hemorrhage with mass effect 1
• Traumatic brain injury with diffuse cerebral edema 3, 6
• Subarachnoid hemorrhage patients (though synthetic colloids show worse outcomes in this population) 1
• Patients with baseline elevated ICP requiring osmotic therapy 1, 5

Mortality Risk

• Older adults with cardiogenic shock requiring CRRT face significantly higher in-hospital mortality 1
• Patients requiring CRRT in the ICU have higher mortality throughout hospitalization, though long-term dialysis dependence rates are similar between age groups 1

Critical Pitfalls to Avoid

• Never use hypotonic solutions (Ringer's Lactate) in acute brain injury patients, as this increases mortality (HR 1.78, p=0.035) 1
• Do not fluid restrict hyponatremic patients with cerebral salt wasting, as this causes cerebral infarction 1
• Avoid hypertonic large-volume glucose exchanges in peritoneal dialysis patients with brain injury 1
• Do not assume normal serum magnesium excludes deficiency in critically ill patients, as hypomagnesemia prevalence reaches 60-65% and affects outcomes 7