Hemofiltration

Hemofiltration

In the field of medicine, hemofiltration, also known as haemofiltration, is a renal replacement therapy akin to hemodialysis primarily utilized in intensive care settings, predominantly for acute renal failure cases. It involves slow continuous therapy sessions lasting typically between 12 to 24 hours and conducted daily. During hemofiltration, a patient's blood is routed through a tubing system (a filtration circuit) via a machine to a semi-permeable membrane (the filter) where waste products and excess water are extracted. Replacement fluid is then added, and the purified blood is returned to the patient.

Similar to dialysis, hemofiltration achieves solute movement across a semi-permeable membrane, albeit through convection rather than diffusion. Unlike dialysis, no dialysate is used in hemofiltration. Instead, positive hydrostatic pressure propels water and solutes across the filter membrane from the blood compartment to the filtrate compartment, from where it is drained. This convection-based method ensures the removal of solutes of various sizes at a similar rate, overcoming the slower removal rate of larger solutes typically seen in hemodialysis.

Hemofiltration is occasionally combined with hemodialysis, termed hemodiafiltration, where blood is pumped through the blood compartment of a high flux dialyzer. This technique involves a high rate of ultrafiltration, necessitating the infusion of substitution fluid directly into the blood line to replace the removed fluid. Although dialysis solution is also passed through the dialysate compartment, this combined approach ensures effective removal of both large and small molecular weight solutes.

These treatments can be administered intermittently or continuously, with the latter often employed in intensive care units. Continuous treatments may last 8-12 hours (slow extended hemofiltration) or be performed continuously (continuous hemofiltration or continuous veno-venous hemofiltration). Hemodiafiltration, another widely used approach, involves combining hemodialysis and hemofiltration. In the United States, commercially prepared, prepackaged, and sterile substitution fluid is commonly used in continuous therapies to circumvent regulatory issues associated with on-line creation of replacement fluid from dialysis solution.

In slow continuous therapies, blood flow rates typically range from 100-200 ml/min, with access usually established through a central venous catheter placed in one of the large central veins. Native access sites for hemodialysis are generally unsuitable for continuous hemofiltration due to the prolonged residence of access needles potentially damaging such sites.

There remains debate regarding whether intermittent on-line hemodiafiltration (IHDF) yields superior outcomes compared to hemodialysis in outpatient settings. While some observational studies in Europe have suggested favorable outcomes with IHDF, definitive conclusions await randomized controlled clinical trials. Additionally, comparisons between IHDF and hemodialysis using low-flux membranes have muddied the waters, as benefits observed may stem more from membrane type than the addition of convective transport to dialysis.