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Hemodialyzer Instrinsic Clearance for Urea (K0A) and Estimation of in Vivo Urea Clearance (K)

Description

The intrinsic clearance of a hemodialyzer (mass transfer area coefficient, or K0A) can be calculated from in vitro data when the blood and dialysate flow rates are known. When the intrinsic clearance of the hemodialyzer is known, then the in vivo urea clearance can be calculated. The actual in vivo urea clearance is less than the theoretical clearance due to the need to correct for blood water content, cardiopulmonary recirculation, access recirculation and blood flow errors.


 

instrinsic clearance K0A =

= (A) / (B) * (LN (C/D))

 

where:

• A = ((blood flow rate in mL/min) * (dialysate flow rate in mL/min))

• B = ((blood flow rate in mL/min) - (dialysate flow rate in mL/min))

• C = 1 - ((in vitro urea clearance for flow conditions) / (blood flow rate in mL/min))

• D = 1 - ((in vitro urea clearance for flow conditions) / (dialysate flow rate in mL/min))

 

Z =

= ((intrinsic clearance for hemodialyzer) / (blood flow rate in mL/min)) * (1 - (E))

 

theoretical in vitro value =

= (blood flow rate in mL/min) * (EXP(Z) - 1) / (EXP(Z) - (E))

 

where:

• E = ((blood flow rate in mL/min) / (dialysate flow rate in mL/min))

 

estimated in vivo urea clearance in mL/min =

= (theoretical in vitro value) * (percent reduction for corrections)

 

where:

• Corrections are the adjustments factors such as blood water content, blood pump calibration, cardiopulmonary recirculation, etc.

 


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Specialty

ICD-10