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Continuous Renal Replacement Therapy (CRRT) Any extracorporeal blood purification therapy intended to substitute for impaired renal function over an extended.

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Presentation on theme: "Continuous Renal Replacement Therapy (CRRT) Any extracorporeal blood purification therapy intended to substitute for impaired renal function over an extended."— Presentation transcript:

1 Continuous Renal Replacement Therapy (CRRT) Any extracorporeal blood purification therapy intended to substitute for impaired renal function over an extended period of time and applied for or aimed at being applied for 24 hours /day. Bellomo R., Ronco C., Mehta R, Nomenclature for Continuous Renal Replacement Therapies, AJKD, Vol 28, No. 5, Suppl 3, November 1996

2 In general: Severe acid-base disorders Severe electrolyte abnormalities Refractory volume overload Uremia Intoxications Intensive Care Severe septic shock

3 Reduces hemodynamic instability preventing secondary ischemia Precise Volume control/immediately adaptable Uremic toxin removal Effective control of uremia, hypophosphatemia, hyperkalemia Acid base balance Rapid control of metabolic acidosis Electrolyte management Control of electrolyte imbalances Management of sepsis/plasma cytokine filter

4 Vascular access Blood flows Machinery Dialyzer Circuit volume Dialysate/ replacement fluid rates Anticoagulation

5 Vascular Access Double lumen catheter Catheter able to provide sufficient blood flow 11 French and greater Avoid kinking Secure connections, make them visible Right size at the right place

6 Principles Vessel(s) and catheters should be large enough to permit blood flow rates > 300 mls/min Problems Poor flow (high positive/negative pressures) Bleeding Clotting Infection Venous stenosis

7 Access recirculation may limit clearances Subclavian 4.1% Femoral 13.5 cm - 22.8% Femoral 19.5 cm - 12.6% (@Blood flow 300 ml/min) More problematic in IHD than CRRT.

8 Diffusion Ultrafiltration Diffusion + Ultrafiltration Adsorbtion


10 Pressure Membrane Uf Uf The transfer of solute in a stream of solvent, across a semi- permeable membrane, mediated by a hydrostatic force Membrane Coffee maker analogy of Ultrafiltration Removal of large volumes of solute and fluid via convection

11 MembraneBloodDialysate/Ultrafiltrate

12 MembraneBlood Ultrafiltrate

13 MembraneBlood Ultrafiltrate

14 Convection: The movement of solutes with a water-flow, solvent drag, the movement of membrane-permeable solutes with ultra filtered water Blood In Blood Out to waste (from patient) (to patient) HIGH PRESS LOW PRESS

15 SCUF Slow Continuous Ultrafiltration n Fluid removal n Minimal solute clearance

16 SCUFCVVH Replacement fluid Removal of large volumes of solute and fluid via convection Replacement of excess UF with sterile replacement fluid Convective solute clearance

17 CVVH Continuous Veno-Venous Hemofiltration n Fluid removal n Fluid replacement n Solute clearance n Convection n Minor amount diffusion

18 Hemofiltration clearance (Cl HF = Q f x S) Q f = Ultrafiltration rate S = Seiving coefficient Hemodialysis clearance (Cl HD = Q d x S d ) Q d = Dialysate flow rate S d = Dialysate saturation Hemodialfiltration clearance Cl HDF = (Q f x S) + (Q d x S d )

19 Capacity of a solute to pass through the hemofilter membrane S = C uf / C p C uf = solute concentration in the ultrafiltrate C p = solute concentration in the plasma S = 1Solute freely passes through the filter S = 0Solute does not pass through the filter

20 Ratio of solute concentration in ultrafiltrate to solute concentration in blood

21 Protein binding Only unbound drug passes through the filter Protein binding changes in critical illness Drug membrane interactions Adsorption of proteins and blood products onto filter Related to filter age Decreased efficiency of filter


23 Solute clearance by diffusion Suitable for removal of small molecules, and most middle molecules

24 Dialysis The use of diffusion (dialysis fluid) to achieve clearance

25 MembraneBloodDialysate

26 MembraneBloodDialysate

27 MembraneBloodDialysate

28 Dialysate Out Dialysate In Blood In Blood Out to waste (from patient) (to patient) HIGH CONCENTRATIONLOW CONCENTRATION

29 CVVHD Continuous Veno-Venous Hemodialysis n Fluid removal n Solute removal (small molecules) n Counter-current dialysis flow n Diffusion n Back filtration Dialysate

30 S d = C d / C p C d = solute concentration in the dialysate C p = solute concentration in the plasma Decreasing dialysate saturation Increasing molecular weight Decreases speed of diffusion Increasing dialysate flow rate Decreases time available for diffusion

31 Countercurrent dialysate flow (10 - 30 ml/min) is always less than blood flow (100 - 200 ml/min) Allows complete equilibrium between blood serum and dialysate Dialysate leaving filter will be 100% saturated with easily diffusible solutes Diffusive clearance will equal dialysate flow

32 Must contain: Sodium Calcium (except with citrate) Base (bicarbonate, lactate or citrate) May contain: Potassium Phosphate Magnesium

33 The Machine….

34 CVVHDF CVVHDF Continuous Veno-Venous Hemodiafiltration Replacement S Access Return Effluent Dialysate n Fluid removal n Solute removal (small and larger solutes) n Diffusion plus Convection

35 Range from 10 to 450 ml/min Average 125-150 ml/min Higher blood flow could decrease filter clotting Factors affecting QB : - Catheter lumen size - Blood viscosity

36 Effect of filtration on CVVH Hematocrit 30% Hematocrit 60% A filtration fraction of more than 25 - 30% greatly increases blood viscosity within the circuit, risking clot and malfunction.

37 The degree of blood dehydration can be estimated by determining the filtration fraction (FF), which is the fraction of plasma water removed by ultrafiltration: FF(%) = (UFR x 100) / QP where QP is the filter plasma flow rate in ml/min.

38 None (- if marked coagulopathy) Unfractionated heparin LMW Heparin Citrate Direct Thrombin Inhibitors r-Hirudin Argatroban Prostacycline Assessment: Need ongoing anticoagulation Risk of bleeding with heparin 2% per day 3.5-10% of deaths 25% of new hemorrhagic episodes

39 Decrease in dialysis dose Wasted nursing time Increase in cost

40 Dose = amount of solute clearance Modifications required based on: Patient weight Interruptions Recirculation

41 Loading doses Loading dose depends solely on volume of distribution Maintenance doses Standard reference tables Base on measured loses Will the drug be removed? Pharmacokinetic parameters Protein binding < 70 - 80% Normal values may not apply to critically ill patients Volume of distribution < 1 L/kg Renal clearance > 35% How often do I dose the drug? Haemofiltration: GFR 10 - 20 ml/min Haemofiltration with dialysis: GFR 20 - 50 ml/min

42 Frequent blood level determinations Aminoglycosides, vancomycin Reference tables Bennett's tables or the PDR recommendations require an approximation of patient's GFR Using Bennett's or the PDRs tables, in most CVVH patients, drug dosing can be adjusted for a GFR in the range of 10 to 50 ml/min


44 Limited to case reports or series of patients Different filter brands, sizes, flow rates Limited information in many reports Artificial models and predictions have no clinical value

45 Elimination > Blood flow = > Elimination > Dialysate flow = > Elimination Free available drug

46 Elimination > Water solubility = > Elimination





51 Mode Clinically still part of the debate (sepsis vs. ARF) Dose Ronco Trial Renal Study ATN Trial High Volume Ultrafiltration IHD vs CRRT No diference in outcome in a RCT Anticoagulation

52 World practice HVUF Ongoing dilemas in CRRT


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