Slow Continuous Ultrafiltration

Slow continuous ultrafiltration (SCUF) - SCUF is generally used for fluid overloaded patients whose bodies have adjusted to diuretic drugs.  

In SCUF therapy, a patient's blood is pumped through a hemofilter, plasma water passes through the hemofilter membrane is pumped into a waste bag.  SCUF is performed continuously over a longer period of time, up to days.  Unlike CVVHD or CVVHDF no dialysate is used to help convey impurities from the blood through the filter and into the effluent.  Unlike CVVHF or CVVHDF, no replacement fluid is used.  Figure 1 shows a typical SCUF setup (while the drawing looks simple, it shows the information accurately).

 Figure 1- A diagram showing typical SCUF set up including fluid pathways and components.

Anticoagulation is not shown in the diagram.

The hemofilter, or dialyzer, has two chambers, one for the patient's blood and in this case, one for the effluent. A thin membrane separates these two parts.  Blood cells, protein and other large molecules remain in the patient's blood because they are too big to pass through the membrane. Smaller waste products in the blood, such as urea, creatinine, potassium and extra fluid pass through the membrane and into the effluent.  In typical hemodialysis the dialyzer is often reused, however, in SCUF and other CRRT therapies, the hemofilter (and all the rest of the tubing set) is generally used once and then disposed of ensuring that the system is sterile.

In SCUF (and CRRT in general) the tubing has colored stripes to help identify its purpose:  

  • Red striped tubing is the access line, it moves blood from the patient to the hemofilter.    
  • Blue striped tubing is the return line, it is used to convey blood from the hemofilter back to the patient. 
  • Yellow striped tubing is the effluent line, it removes the effluent from the dialyzer into a waste or effluent bag.

There may be clear tubing that moves the anticoagulant into the tubing circuit.  Certain sections of tubing may be clear to fill certain purposes, clear tubing works best for air detectors and blood detectors, so tubing that goes through those is generally clear, the pump tubing sections are made from a more durable material and are usually clear as well.

The various fluids are moved through the tubing set by roller or peristaltic pumps.  Special more durable sections of the tubing are inserted into these pumps and the pumps move the fluid through the tubing.  The pumps do not contact the blood or other fluids in any way.