What is the recommended approach for managing dialysis in patients with impaired renal function in the neurocritical care setting?

Management of Dialysis in Neurocritical Care

Primary Recommendation

In neurocritical care patients requiring dialysis, continuous renal replacement therapy (CRRT) should be the preferred modality over intermittent hemodialysis due to superior hemodynamic stability and reduced risk of worsening cerebral edema and intracranial pressure. 1

Modality Selection Based on Clinical Scenario

When to Choose CRRT (Preferred in Neurocritical Care)

• Use CRRT as first-line therapy in patients with hemodynamic instability, elevated intracranial pressure, or cerebral edema 1, 2
• CRRT provides slow, continuous solute removal that mimics native kidney function with dialysate/ultrafiltrate flow rates yielding clearances similar to physiologic GFR 3
• Superior volume control without rapid osmotic shifts that can exacerbate cerebral edema 4
• Hemodynamic tolerance is significantly better than intermittent HD in critically ill patients 2

When Intermittent HD May Be Considered

• Only use intermittent HD when rapid toxin removal is absolutely necessary (e.g., severe hyperammonemia >1,000 μmol/L) 4, 5
• Be aware that intermittent HD causes hypotension and rapid osmotic shifts that worsen cerebral edema and increase risk of cerebral herniation in patients with raised intracranial pressure 4
• If HD is used, it should be followed immediately by CRRT to prevent rebound effects 4

Specific Neurocritical Care Scenarios

Hyperammonemia with Encephalopathy

For ammonia levels >1,000 μmol/L (1,703 μg/dl) with severe encephalopathy, initiate high-dose continuous venovenous hemodialysis (CVVHD) with blood flow rate 30-50 mL/min and dialysis fluid flow rate/blood flow rate ratio >1.5 5

• Start nitrogen-scavenging agents (sodium benzoate 250 mg/kg for weight <20 kg or 5.5 g/m² for weight >20 kg) while preparing for dialysis 4, 5
• For ammonia 301-499 μmol/L with moderate-to-severe encephalopathy, initiate scavenger treatment while preparing for dialysis 4
• Clinical status should be the primary determinant for initiating kidney replacement therapy, not rigid ammonia thresholds 4
• Consider hybrid therapy: start with HD for rapid reduction, then transition to CRRT once ammonia <200 μmol/L on two consecutive hourly measurements 4

Uremic Encephalopathy

Initiate dialysis when patients develop symptoms attributable to kidney failure including cognitive impairment, seizures, or progressive neurological deterioration 4

• For patients refusing dialysis with uremic encephalopathy, implement conservative management with loop diuretics, sodium polystyrene sulfonate for electrolyte control, and nitrogen-scavenging agents if severe hyperammonemia contributes 6
• All patients refusing dialysis should receive comprehensive palliative care with regular symptom screening 6

Post-Dialysis Seizures

Administer anticonvulsants immediately (diazepam, phenytoin, or levetiracetam 10 mg/kg, maximum 500 mg every 12 hours with renal dose adjustment) 7

• Check electrolytes (sodium, potassium, calcium, phosphate) and plasma aluminum levels if toxicity suspected (>150-350 μg/L indicates toxicity) 7
• Prevent by using more frequent, shorter dialysis sessions rather than fewer longer sessions 7
• Avoid aluminum-containing phosphate binders, especially with citrate salts which enhance aluminum absorption 7

CRRT Prescription Parameters

Dosing

Prescribe CRRT at 20-25 mL/kg/hour of effluent flow rate (dialysis or hemofiltration) 8

• This represents the standardized dose for continuous RRT in critically ill patients 8
• Delivered dose is typically less than prescribed dose, so monitor actual delivery 2
• Use weight-adjusted ultrafiltration flow rate (mL/kg/h) as surrogate for prescribed dialysis dose 2

Monitoring

• Measure delivered dose using dialysate-side quantification (KD) rather than blood-based urea kinetic modeling 9
• Assess filter function every 12 hours by calculating blood urea nitrogen to dialysis fluid urea nitrogen ratios 9
• Monitor fluid balance closely as net ultrafiltration may be as important as blood purification in critically ill patients 8

Anticoagulation Considerations

In neurocritical care patients at high bleeding risk, CRRT can be performed without anticoagulation or with regional citrate anticoagulation 1

• Regional citrate anticoagulation is preferred when anticoagulation is needed but systemic anticoagulation is contraindicated 9
• Pre-dilution mode reduces need for anticoagulation compared to post-dilution 9

Critical Pitfalls to Avoid

• Never use peritoneal dialysis for hyperammonemia—it is significantly less efficient than HD or CRRT 4
• Do not delay dialysis initiation in deteriorating patients while waiting for specific ammonia thresholds 4
• Avoid intermittent HD as sole therapy in patients with elevated intracranial pressure due to risk of osmotic shifts and hypotension-induced herniation 4
• Do not extrapolate intermittent hemodialysis drug dosing recommendations to CRRT—clearances differ substantially 3
• Ensure proper vascular access planning: avoid internal jugular sites and preserve brachial/radial arteries for future dialysis access 4

Multidisciplinary Decision-Making

The decision regarding dialysis modality should be made jointly by nephrology, critical care, and neurology teams, considering institutional resources, patient hemodynamic status, and neurological condition 4

• Institutional preference and local facilities influence modality choice, but hemodynamic stability and intracranial pressure concerns should drive selection in neurocritical care 4
• For patients with uncertain prognosis, offer time-limited trial of dialysis with planned reassessment 6