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 |