Hemofiltration

Continuous Venon Venous HaemoDIALAfiltration (CVVHDF)

Hemofiltration, also referred to as haemofiltration, is a form of renal replacement therapy closely related to hemodialysis. Primarily applied in the context of intensive care, this procedure is predominantly used to treat acute renal failure. Hemofiltration sessions are continuous, often spanning 12 to 24 hours and are typically performed on a daily basis. The process entails circulating a patient's blood through a filtration system to remove waste products and excess water.

Procedure Overview

During hemofiltration, blood is channeled through tubing, referred to as a filtration circuit, via a specialized machine. This blood then encounters a semipermeable membrane known as the filter. Here, unwanted waste products and water are sifted out. Subsequently, a replacement fluid is introduced before the cleansed blood is rerouted back to the patient.

Principle of Hemofiltration

While there are similarities between hemofiltration and dialysis in that both involve solute migration across a semi-permeable membrane, the mechanisms governing this movement differ. In hemofiltration, the driving force is convection, as opposed to diffusion in dialysis. Hemofiltration does not employ dialysate. Instead, a hydrostatic pressure propels water and solutes from the blood side to the filtrate side of the membrane, leading to their drainage. This convective movement ensures that solutes, regardless of their size, traverse the membrane at comparable rates, addressing the challenge posed by the slower diffusion rate of larger solutes in hemodialysis.

Replacement Fluid Composition

A crucial step in hemofiltration is the addition of an isotonic replacement fluid to compensate for fluid volume and electrolyte loss. It is imperative that this fluid be of exceptional purity as it is introduced directly into the blood segment of the external circuit. Common constituents of the hemofiltration fluid are lactate or acetate, which function as precursors for bicarbonate generation, or bicarbonate itself. Utilizing lactate may pose complications for patients battling lactic acidosis or severe liver conditions, as these scenarios can impede the lactate-to-bicarbonate conversion. For such individuals, bicarbonate is the preferred base.

Hemodiafiltration

Hemodiafiltration is an advanced technique that amalgamates hemofiltration and hemodialysis. Here, blood courses through the blood compartment of a high flux dialyzer. A rapid ultrafiltration rate ensures substantial water and solute transfer from blood to dialysate, necessitating the infusion of a substitution fluid directly into the blood circuit. Concurrently, a dialysis solution circulates through the dialysate segment of the dialyzer. This combined approach is advantageous as it facilitates efficient removal of both large and smaller molecular weight solutes.