Biocompatibility
- The rate of blood flow from the patient towards the filter
- Blood flow rates are typically slower than in intermittent dialysis, ranging from 150-200mL/min
Flux
- The rate at which ultrafiltrate is produced by hydrostatic pressure across the membrane during convective therapies
- It is influenced by the blood flow rate and the filtration fraction
Adsorption
- The flow rate of dialysis fluid in dialytic therapies
- Standard flow rates range from 8-50 mL/min
Thickness
- The effluent flow rate is the equivalent to ultrafiltration rate Quf in continuous haemofiltration, Qd in continuous haemodialysis, and both Quf & Qd in continuous hemodiafiltration
- It is analogous to the ‘dose’ in continuous therapies
- Dosing is weight-based and is typically prescribed at a dose ranging from 20 mL/kg/hr to 35 mL/kg/hr
Surface area
- Techniques in which produce a volume of ultrafiltrate require replacement of this fluid with a substitute fluid to prevent significant loss of volume.
- The rate of substitution fluid describes the rate at which this replacement fluid is added to the plasma
Material
- Represents the overall rate of fluid removal
- It is the difference between the total effluent removed (Qef) minus the volume of replacement therapy
- The fluid removal rate can be tailored by the machine to meet the total removal goal of the patient
- There is no conclusive evidence that any specific membranes improve the outcome
- In practice, most filters used for CRRT are:
- Synthetic, high-flux membranes
- Surface area of 0.6–1.2m2
- Pore size allowing the passage of molecules up to 50,000 Daltons