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Table 2 Fluids and flows in continuous renal replacement therapy

From: Nomenclature for renal replacement therapy in acute kidney injury: basic principles

Flowrate Symbol Unit of measure Definitions and comments
Blood flowrate QB ml/min Depends on:
- modality
- vascular access
- hemodynamic stability of the patient
Plasma flowrate QP ml/min Approximated as: QP = (1 – HCT) ∙ QB
where HCT = hematocrit
Ultrafiltration flowrate QUF ml/h Total volume of fluid removed in the filter by positive TMP per unit of time: QUF = QUF NET + QR.
Depends on:
- blood flow rate
- filter and membrane design
- transmembrane pressure (TMP)
- membrane ultrafiltration coefficient and surface area
Net ultrafiltration flowrate (Δ weight flowrate) (weight loss flowrate) QUF NET ml/h Net volume of fluid removed from the patient by the machine per unit of time
Plasma ultrafiltration flow rate QP-UF ml/h Total volume of plasma removed in the plasma filter by TMP per unit of time
Replacement flowrate
(Substitution flow rate)
(Infusion flowrate)
QR PRE
QR POST
QR PRE/POST
ml/h Sterile fluid replacement can be:
- upstream of filter (pre-replacement, pre-infusion or pre-dilution): reduced depurative efficiency but better filter life
- downstream of filter (post-replacement, post-infusion or post-dilution): higher depurative efficiency but lower filter life
- both upstream and downstream of filter (pre-post replacement, pre-post infusion or pre-post dilution): compromise between the two modalities
Replacement plasma flow rate QP-R ml/h Replacement of plasma downstream of the plasma filter
Dialysate flowrate QD ml/h Volume of dialysis fluid running into the circuit per unit of time
Effluent flowrate QEFF ml/h Waste fluid per unit of time coming from the outflow port of the dialysate/ultrafiltrate compartment of the filter:
QEFF = QUF + QD = QUF NET + QR + QD