What type of dialyzer is used in poisoning cases, specifically for toxin removal from the blood?

Type of Dialyzer Used in Poisoning

For most poisonings requiring extracorporeal toxin removal, intermittent hemodialysis with high-flux dialyzers is the preferred modality, optimized with higher blood flow rates and larger surface area membranes to maximize clearance. 1

Primary Dialyzer Selection

High-Flux Hemodialysis Membranes

• High-flux dialyzers should be used when hemodialysis is indicated for poisoning, as they provide superior clearance of middle-molecular-weight toxins compared to low-flux membranes 1
• High-flux is defined as β2-microglobulin clearance of at least 20 mL/min, though modern dialyzers achieve substantially higher clearances 1
• These membranes are particularly effective for water-soluble toxins with low protein binding 2

Optimization Parameters for Toxin Removal

• Use dialyzers with the largest available surface area to enhance clearance 1
• Maximize blood flow rates (typically 300-400 mL/min) 1
• Optimize dialysate flow rates to maintain concentration gradients 1
• Consider dialysate temperature reduction to minimize hemodynamic compromise 1

Modality Selection by Poison Type

First-Line: Intermittent Hemodialysis

Intermittent hemodialysis is recommended as the primary extracorporeal treatment for most dialyzable poisons including salicylates, toxic alcohols (methanol, ethylene glycol), lithium, and hydrophilic beta-blockers (atenolol, sotalol) 1, 3, 4

• Provides the highest clearance rates (can exceed 100 mL/min for salicylates) 1
• Most efficient for removing water-soluble toxins with low volumes of distribution 3, 5
• Allows rapid correction of metabolic acidosis 1

Alternative Modalities (When Hemodialysis Unavailable)

If intermittent hemodialysis is not available, the following alternatives can be considered in descending order of preference:

1. Hemoperfusion: For highly protein-bound toxins with low volume of distribution (e.g., carbamazepine, theophylline, certain beta-blockers like carvedilol) 1, 4

2. Continuous Renal Replacement Therapy (CRRT): When hemodynamic instability precludes intermittent hemodialysis AND net ultrafiltration is required 1

   • Note: CRRT provides lower clearance rates than intermittent hemodialysis 1
   • May be better tolerated in unstable patients requiring fluid removal 1

3. Sustained Low-Efficiency Dialysis (SLED) or Prolonged Intermittent Renal Replacement Therapy (PIRRT): Intermediate options when intermittent hemodialysis is unavailable 1

Ineffective or Inferior Modalities

• Peritoneal dialysis: Clearance rates (≤10 mL/min) are several-fold inferior to hemodialysis and should not be used when hemodialysis is available 1
• Therapeutic plasma exchange (plasmapheresis): Limited role; only considered for highly protein-bound toxins, but carries significant risks including mortality (0.05%), hemodynamic shifts, infection, and removal of clotting factors 2
• Exchange transfusion: Historical use in infants; removes only 20-25% of toxin burden 1

Specific Poison Considerations

Toxic Alcohols (Methanol, Ethylene Glycol)

• Use high-flux hemodialysis when serum concentration ≥50 mg/dL or significant metabolic acidosis present 6
• Dialyzer urea clearance can predict toxic alcohol clearance (use 80% of manufacturer-specified urea clearance at observed blood flow) 7, 8
• Increase dosing frequency of fomepizole to every 4 hours during hemodialysis due to dialyzability 6

Salicylates

• Hemodialysis recommended when concentration >7.2 mmol/L (100 mg/dL) in acute poisoning or >6.5 mmol/L (90 mg/dL) in chronic poisoning 1
• Hemodialysis clearance can surpass 100 mL/min, providing at least 3 times the clearance of urinary alkalinization alone 1

Beta-Blockers (Atenolol, Sotalol)

• Intermittent hemodialysis is most efficient for hydrophilic agents 1
• For sotalol: maintain serum magnesium >1 mmol/L and potassium 4.5-5 mmol/L during dialysis to prevent torsades de pointes 1
• Consider hemoperfusion or high-cutoff dialysis for highly protein-bound agents (penbutolol, oxprenolol, carvedilol) 1

Barbiturates

• Long-acting barbiturates (phenobarbital) are dialyzable with hemodialysis clearance up to 188 mL/min 1
• Short-acting barbiturates are moderately dialyzable 1
• Hemoperfusion can remove >30% of ingested dose in a single 5-hour session 1

Common Pitfalls to Avoid

• Do not delay hemodialysis while attempting less effective modalities like urinary alkalinization alone in severe poisonings 1
• Avoid using polycarbonate syringes or needles when administering fomepizole, as it can compromise syringe integrity 6
• Do not cease dialysis based solely on toxin concentration; clinical improvement (hemodynamic stability, resolution of acidosis, adequate end-organ perfusion) should guide cessation 1
• Ensure appropriate electrolyte concentrations in dialysate (avoid low potassium, calcium, magnesium) to minimize dysrhythmias and hemodynamic compromise 1, 9
• Minimize net ultrafiltration in poisoned patients without volume overload to reduce hypotension risk 1