What is extracorporeal blood purification?

6 MIN READ

Hemoadsorption, hemofiltration and plasma exchange are often grouped together. They work differently, and the distinction matters at the bedside.

The principle

Extracorporeal blood purification describes any therapy that circulates blood outside the body to remove circulating substances before returning it. The therapies differ in what they remove and by what mechanism.

Haemodialysis and haemofiltration remove small and middle molecules across a membrane, driven by diffusion or convection. Plasma exchange removes plasma wholesale and replaces it. Hemoadsorption instead passes blood through a cartridge filled with a sorbent whose surface binds target molecules directly, so removal depends on binding affinity rather than molecular size alone.

Why adsorption suits inflammatory mediators

Endotoxin and the major inflammatory cytokines are middle-to-large molecules that membranes clear poorly. A sorbent surface can be engineered with both hydrophobic and charge-based binding sites, allowing a single cartridge to capture a broad spectrum of mediators — described as multimodal adsorption.

Because binding is a surface phenomenon, capacity is finite: cartridges are designed for a defined treatment duration, after which the sorbent is saturated and the cartridge is replaced or therapy is concluded.

Where it sits in the treatment pathway

Blood purification is adjunctive. It does not treat the source of infection, restore volume or replace vasoactive support; it removes mediators that are driving the shock state while the underlying cause is addressed.

Practically, this means the therapy competes on timing rather than on substitution: the clinical question is whether mediator removal is started early enough in a deteriorating patient to change the trajectory.

Circuit considerations

Cartridges can run on a standalone blood pump or be integrated in series with an existing CRRT or ECMO circuit. Integration avoids a second vascular access and additional capital equipment, but requires the unit to agree pressure monitoring, anticoagulation and alarm handling in advance.

For paediatric patients, extracorporeal volume relative to circulating volume becomes the limiting factor, which is why dedicated paediatric devices exist rather than adjusted adult protocols.

This article is general educational information for healthcare professionals and is not clinical advice or a treatment recommendation. Always refer to the current instructions for use and local clinical guidance.