How do hemodialysis and hemoperfusion differ in mechanism, indications, and practical considerations?

Hemodialysis vs Hemoperfusion: Key Differences

Hemodialysis and hemoperfusion are fundamentally different extracorporeal blood purification techniques: hemodialysis removes solutes primarily through diffusion across a semipermeable membrane (and secondarily through convection), while hemoperfusion removes substances through adsorption to activated charcoal or resin beads contained in a cartridge. 1, 2, 3

Mechanism of Action

Hemodialysis

• Removes solutes primarily through diffusion across a concentration gradient from blood to dialysate solution, following Fick's law 2
• Convection (solvent drag) occurs secondarily during ultrafiltration, particularly important for larger molecular weight molecules 2
• Blood flows on one side of a semipermeable membrane while dialysate flows countercurrent on the other side 4
• Achieves only 10-20% of normal renal clearance for substances like urea or creatinine 1, 2
• Most effective for small, water-soluble molecules with low protein binding and low volume of distribution 5, 6

Hemoperfusion

• Removes substances through direct adsorption to activated charcoal or synthetic resin beads in a cartridge 1, 3
• Blood is pumped directly through the adsorbent material without a dialysate solution 6
• Does not rely on concentration gradients or molecular size limitations of membranes 3
• Superior clearance for substances that bind to charcoal, regardless of molecular weight or protein binding 6
• Can achieve clearance rates several-fold higher than hemodialysis for adsorbable compounds 1

Clinical Indications

Hemodialysis is Preferred For:

• Methanol poisoning (dialyzable toxin) 5, 6
• Ethylene glycol poisoning (dialyzable toxin) 5, 7
• Salicylate poisoning - intermittent hemodialysis is the preferred modality 1
• Lithium poisoning (most common toxin removed by hemodialysis in recent years) 7
• Isopropyl alcohol poisoning 5
• Long-acting barbiturates (phenobarbital) - hemodialysis is preferred over hemoperfusion 1
• Atenolol and sotalol poisoning (beta-blockers) - intermittent hemodialysis is recommended 1

Hemoperfusion is Preferred For:

• Theophylline poisoning - hemoperfusion provides superior clearance 1, 5, 6, 7
• Carbamazepine poisoning (became most frequent indication 2001-2005) 7
• Short-acting barbiturates - when hemodialysis is unavailable 1
• Substances with high protein binding or lipid solubility that are poorly cleared by hemodialysis 5, 8

Either Modality Acceptable:

• Barbiturate poisoning - both are dialyzable, but hemodialysis preferred when available 1
• Salicylate poisoning - hemoperfusion acceptable if hemodialysis unavailable 1

Practical Considerations

Hemodialysis Advantages:

• Widely available in most hospitals with nephrology services 1
• Corrects fluid overload, electrolyte abnormalities, and acid-base disturbances simultaneously 1
• Lower complication rates compared to older hemoperfusion technology 6
• Can be performed continuously (CRRT) for hemodynamically unstable patients 1
• Standard equipment and expertise readily available 1

Hemoperfusion Advantages:

• Higher clearance rates for adsorbable toxins (can exceed 290 mL/min for phenobarbital vs 174 mL/min with hemodialysis) 1
• Not limited by molecular weight or protein binding of the toxin 3, 8
• More effective for lipid-soluble compounds 5

Hemoperfusion Disadvantages:

• Limited availability - use has declined dramatically (from 53 to 12 cases per million poison center calls from 1985-2005) 7
• Historical bioincompatibility issues: hypotension, thrombocytopenia, leukopenia, hypocalcemia 6, 3
• Does not correct fluid or electrolyte abnormalities 6
• Blood loss and hematoma risk 6
• Requires specialized cartridges that may not be stocked 1
• Modern biocompatible sorbents have improved safety but are not universally available 3

Combination Therapy

• Hemoperfusion combined with hemodialysis can be used when both toxin removal and metabolic correction are needed 1
• The combination showed small advantage over high-flux hemodialysis alone for aluminum removal 1
• Sequential or alternating treatments may be considered for complex poisonings 1

Trends in Clinical Practice

• Hemodialysis use has increased from 231 to 707 cases per million poison center calls (1985-2005) 7
• Hemoperfusion use has declined from 53 to 12 cases per million calls in the same period 7
• Peritoneal dialysis is rarely used for toxin removal (decreased to 1.6 per million by 1991) 7
• Valproate and acetaminophen dialysis increased despite limited evidence for acetaminophen 7

Common Pitfalls

• Do not use hemodialysis for highly protein-bound or lipid-soluble toxins (tricyclic antidepressants, chloroquine, paraquat, flecainide) where it provides minimal benefit 6
• Do not delay hemoperfusion for theophylline toxicity when it is the superior modality 5, 6
• Do not assume hemoperfusion is unavailable without checking - it may be accessible at tertiary centers 1
• Do not use hemoperfusion alone when metabolic derangements require correction - combine with hemodialysis or use hemodialysis alone 6
• Extracorporeal removal is only worthwhile if it increases total body clearance by ≥30% 6