Haemoperfusion Basics
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Direct answer
Haemoperfusion passes blood directly over an adsorbent cartridge of activated charcoal or resin, letting poisons that are tightly protein-bound or too large for a dialyser stick to the sorbent instead. It is the modality of choice for severe carbamazepine, phenytoin, phenobarbitone, theophylline and paraquat poisoning, where plasma concentrations and clinical severity justify extracorporeal removal; sometimes it runs in series with haemodialysis to add small-solute clearance. The technique needs higher heparin than dialysis (adsorbents consume clotting factors and platelets), cartridges saturate within about 2-3 hours, and the watchlist is hypotension, thrombocytopenia, hypocalcaemia and charcoal embolism from a ruptured cartridge.
What you must remember
- Principle: adsorption onto a large sorbent surface — no membrane, no dialysate; the cartridge is the treatment.
- Target poisons (protein-bound, large Vd or poorly dialysable): carbamazepine (about 70-80 per cent protein-bound), phenytoin (about 90 per cent), phenobarbitone, theophylline, paraquat, amanita mushroom toxin, some sedatives — whereas lithium, methanol and ethylene glycol belong to haemodialysis, not charcoal.
- Not removed usefully: small water-soluble solutes (urea, potassium, alcohols) — pairing with dialysis covers both classes in mixed poisoning.
- Setup: cartridge primed with saline per insert (usually 1-2 litres, gently, to wash microfines), blood flow 150-250 mL/min, session 2-3 hours until saturation, repeated as levels dictate.
- Anticoagulation is heavier than HD: typically an initial heparin bolus around 2000-3000 units with a continuous infusion, because the sorbent surface is strongly prothrombotic — per unit protocol.
- Complications: thrombocytopenia (platelets adhere to charcoal), hypotension at initiation, hypocalcaemia, hypoglycaemia (rare), leucopenia, and pulmonary charcoal emboli if the cartridge membrane ruptures — filter integrity is checked by visible fines in the venous line.
- Declining indications: modern antidotes and lipid emulsion have narrowed its role, but theophylline and carbamazepine crises still reach Indian ICUs, and examination boards still love the modality logic.
Routing a poisoned patient
Three overdoses arrive in one week. The first is lithium — small ion, no protein binding, total body water distribution: charcoal cannot adsorb it meaningfully and the answer is haemodialysis, ideally early, with flow high enough to clear a toxin that re-equilibrates from cells. The second is carbamazepine — 75 per cent bound to albumin, so the dialyser sees only the free quarter, but the charcoal cartridge binds the drug from both fractions as equilibrium shifts: this is the haemoperfusion case, run at 200 mL/min for three hours, watching for a seizure-free but hypotensive hour one and a platelet count that dips by the next morning. The third is an unknown mixed sedative-plus-alcohol ingestion — here the pragmatic Indian solution is a cartridge in series with a dialyser: the dialyser clears the alcohol and acidosis, the charcoal picks up the protein-bound sedative, one vascular access, one session.
The recurring decision rule is worth memorising as a sentence: dialyse what dissolves, perfuse what binds. Before committing, confirm severity criteria — rising or very high drug level, deteriorating consciousness, refractory seizures or arrhythmia, and failing native clearance — because no poison qualifies for a fistula-sized procedure just on the basis of the name.
Where students slip
The classical MCQ swaps the modalities: methanol or lithium assigned to haemoperfusion, carbamazepine or theophylline assigned to plain dialysis — both wrong, and both common distractor options. The second slip is forgetting the biology of the cartridge: it adsorbs platelets and clotting factors, so bleeding risk and platelet count are monitored, and heparin dosing runs higher than a dialysis session, not lower. Third is duration logic: the cartridge saturates by about 2-3 hours, so extending the session adds nothing — you change the cartridge or stop; and levels rebound after stopping as tissue drug re-equilibrates, which is why repeat sessions are planned rather than one heroic run.
Frequently asked questions
Which poisons are best removed by haemoperfusion rather than haemodialysis?
Heavily protein-bound or large drugs — carbamazepine, phenytoin, phenobarbitone, theophylline and paraquat — adsorb well to charcoal, unlike small water-soluble toxins such as lithium and methanol.
Why does haemoperfusion require more anticoagulation than haemodialysis?
The sorbent surface activates platelets and consumes clotting factors, demanding higher heparin dosing with platelet and bleeding surveillance.
How long does a haemoperfusion cartridge function usefully?
About 2-3 hours before saturation, after which the cartridge is changed or the session ends; drug levels often rebound and repeat sessions are scheduled.
What are the complications of haemoperfusion?
Thrombocytopenia, hypotension at initiation, transient hypocalcaemia and leucopenia, and rare pulmonary charcoal embolism if the cartridge ruptures.
Why combine haemoperfusion with haemodialysis in mixed poisoning?
Running the cartridge in series with a dialyser clears protein-bound drugs by adsorption and small water-soluble toxins by diffusion in a single session through one access.