This document discusses continuous renal replacement therapy (CRRT) which is an extracorporeal blood purification therapy used to substitute for impaired kidney function over an extended period of time. It requires a central venous catheter, extracorporeal circuit, blood pump, and effluent pump. CRRT is indicated for hemodynamically unstable acute kidney injury patients or those with brain injury. Common forms of CRRT include continuous venovenous hemofiltration (CVVH), hemodialysis (CVVHD), and hemodiafiltration (CVVHDF). Anticoagulation is needed to prevent circuit clotting and can include heparin or citrate. Complications include bleeding,

1. Continuous Renal
Replacement
Therapy
DR.G.B.Chandra
SR Nephrology

2. Continuous Renal Replacement Therapy
(CRRT)
• Is an 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 a day.

3. Requirements for CRRT
• A central double-lumen veno-venous
hemodialysis catheter.
• An extracorporeal circuit and a hemofilter
• A blood pump and a effluent pump.
• With specific CRRT therapies dialysate
and/or replacement pumps are required.

4. Indications
• According to 2012 guidelines for AKI:
• Hemodynamically unstable patients.
• AKI with acute brain injury or other causes of
raised ICT or generalized brain edema.

5. Principals of CRRT
• Vascular access.
• Semi-permeable membrane.
• Transport mechanism.
• Dialysate and replacement fluid.

6. Vascular access
• Internal jugular(primary site)
• Subclavian.
• Femoral(least preferred)
• The following are suggested guidelines
for the different sites:
• – RIJ= 15 cm
• – LIJ= 20 cm
• – Femoral= 25 cm
• AV access- not favoured

7. II- Semi-permeable membrane
• The basis of all blood purification
therapies.
• Water and some solutes pass through
the membrane, while cellular components
and other solutes remain behind.

8. Solute clearance- Diffusion

9. Convection
• Movement of solutes through a membrane by
the force of water “solvent drag”.
• The water pulls the molecules along with it as it
flows through the membrane.
• Can remove middle and large molecules, as well
as large fluid volumes.
• Maximized by using replacement fluids.

10. Solute clearance-
Convection(Haemofiltration)

12. IV- Dialysate and replacement
fluid
The dialysate is run on the
opposite side of the filter,
countercurrent to the flow of
the patient’s blood. The
countercurrent flow allows a
greater diffusion gradient
across the entire membrane,
increasing the effectiveness of
solute removal.

13. Dialysates
• Buffers :
a) Lactate based- usual concentration (40-46mM).
Metabolized on 1:1 basis to bicarbonate.
• Should be used in caution with
• Patients with circulatory instability with tissue
hypoperfusion
• With severe liver compromise.
b) Bicarbonate based(buffer of choice, 25-35mM)
c) Citrate based( buffering & anticoagulant property merged).
Used in predilution mode so not used in C-HD/ C-HF.

15. Bicarbonate based solutions
preparations
• Bicarbonate is in equilibrium with carbonic
acid, breaks into H20, CO2, unstable.
• Forms insoluble salts with Ca, Mg in solution
so should be prepared just before use.
• Formulations- 1L 0.45 NS + 35ml
NaHCO3(35mmol)+ 10ml 23% NaCl (40mmol)
+2.1ml of 10% CaCl2
• Final conc- Na- 145, Ca- 2.7meq, HCO3- 33

16. Replacement fluid
• Used to increase the amount of convective
solute removal in CRRT.
• Replacement fluids do not replace anything.
• Fluid removal rates are calculated
independently of replacement fluid rates.
• Can be pre or post filter.

17. Replacement fluid
•The decision to infuse replacement fluids
before or after the filter is made by the
physician.
• Replacement fluids administered prefilter
reduce filter clotting and can be
administered at faster rates (driving higher
convection) than fluids administered postfilter.

19. Renal Repalcement Techniques

20. IHD- Advantages

21. IHD- disadvantages

22. Continuous therapy-Advantages

23. Continuous therapy-Disadvantages

24. Slow Continuous Ultrafiltration
(SCUF)
• The primary indication for SCUF is
• Fluid overload
• without uremia or significant electrolyte imbalance.
e.g. Decompensated heart failure.
• The main mechanism of water transport is
ultrafiltration.
• Other solutes are carried off in small amounts,
but usually not enough to be clinically
significant.

25. Slow Continuous Ultrafiltration
(SCUF)
• The amount of fluid in the effluent bag is the
same as the amount removed from the
patient.
• No dialysate or replacement fluid is used.

26. SCUF

27. Continuous Veno-venous Hemofiltration
(CVVH)
• An extremely effective method of solute removal
and is indicated for uremia or severe pH or
electrolyte imbalance with or without fluid
overload.
• Particularly good at removal of large molecules,
because CVVH removes solutes via convection.

28. Continuous Veno-venous Hemofiltration
(CVVH)
• Solutes can be removed in large quantities while
easily maintaining a net zero or even a positive
fluid balance in the patient.
• The amount of fluid in the effluent bag is equal
to the amount of fluid removed from the patient
plus the volume of replacement fluids
administered.
• No dialysate is used.

29. CVVH

30. Continuous Veno-venous Hemodialysis
(CVVHD)
• Effective for removal of small to medium sized
molecules.
• Solute removal occurs primarily due to diffusion.
• No replacement fluid is used.
• Dialysate is run on the opposite side of the filter.
• Fluid in the effluent bag is equal to the amount
of fluid removed from the patient plus the
dialysate.

31. CVVHD

32. Continuous Veno-venous Hemodiafiltration
(CVVHDF)
• The most flexible of all the therapies, and
combines the benefits of diffusion and
convection for solute removal.
• The use of replacement fluid allows
adequate solute removal even with zero or
positive net fluid balance for the patient.

33. Continuous Veno-venous Hemodiafiltration
(CVVHDF)
• Amount of fluid in the effluent bag equals
the fluid removed from the patient plus the
dialysate and the replacement fluid.
• Dialysate on the opposite side of the filter
and replacement fluid either before or after
the filter.

34. CVVHDF

35. SLED(D) &(F):Hybrid therapy
• Conventional dialysis equipment
• Form of IHD using 6-10 hours session length with
blood flow- 200ml/min,
• dialysate flow- 100-300ml/min
• Online dialysis fluid preparation
• Excellent small molecule detoxification
Fliser, T & Kielstein JT. Nature Clin Practice Neph 2006; 2: 32-39
Berbece, AN & Richardson, RMA. Kidney International 2006; 70: 963-968

36. SLED(D) &(F):Hybrid therapy
• Cardiovascular stability as good as CRRT
• Reduced anticoagulation requirement
• 11 hrs SLED comparable to 23 hrs CVVH
• Decreased costs compared to CRRT
• Phosphate supplementation required
SLED/ SLED-F may be useful as CRRT but there is
paucity of outcomes trials comparing them.

37. Uraemia Clearance

38. Towards targeted therapy

39. Anticoagulation & CRRT
• Heparin: bolus- 2000 -5000 units
Infusion 500- 1000 units/kg/hour.
• Target activated partial thromboplastin time
(aPTT):
• Arterial PTT - 40-45 secs (decrease by 100u/hr
if >45 secs)
• Venous PTT >65secs(increase by 100u/hr if
<65secs)

40. No Anticoagulation
• Platelet count < 50,000/mm3
• INR > 2.0
• aPTT > 60 seconds
• Actively bleeding or with an active bleeding
episode in the last 24 hours
• Severe hepatic dysfunction or recent liver
transplantation
• Within 24 hours post cardiopulmonary bypass or
extra-corporeal membrane oxygenation (ECMO).

41. Anticoagulation & CRRT
• Regional unfractionated Heparin:
a prefilter dose of 1500 units/hour of Heparin,
Protamine postfilter at a dose of 10-12 mg/hour.
• Use of pre dilution mode in C-HF, blood flow
should be kept @200ml/min or higher
• Prostacyclin: rarely used (expensive,
hypotension)
• Citrate: infused pre-filter, Ca must be replaced.

42. Regional Citrate Anticoagulation
(RCA)
• 3mmol of citrate /L to keep post filter ionized
calcium to 0.3-0.4 mmol/L, for effective circuit
anticoagulation.
• ACD- A(anti citrate dextrose form A) is used
(3%trisodium citrate, citric acid and dextrose).
• Swartz protocol- infusion rate is 1.5 times
BFR(ml/min).
• Calcium chloride (20mg/ml) infusion rate
should be 10% of ACD-A infusion rate.

43. Cont
• Ionized calcium is monitored every
• 2hours × 4
• 4hours × 4 for 1st 24 hours
• Then every 6-8 hours.

44. Other anticoagulants
• Lepirudin (eliminated by kidneys)
• Argatroban (eliminated by liver)
• Dalteparin
• Enoxaparin (experience limited)

45. Signs of clotting
• Darkening of blood in extracorporeal circuit
• Coolness of blood in venous line
• Separation of rbcs & plasma in circuit
• In C-HD, filtrate urea nitrogen(FUN) : serum
urea nitrogen(SUN) < 0.6, clotting is imminent.

46. Complications of CRRT
• Bleeding
• Hypothermia
• Electrolyte imbalance
• Acid-base imbalance
• Infection
• Dosing of medications

47. IHD Vs CRRT
• Renal recovery may be better after CRRT than
IHD for ARF.
• Mortality was not affected significantly by RRT
mode.

48. Solute clearance in CRRT (C-HD)
• Primarily determined by dialysate flow rate.
• BFR(50-200 ml/min) should be atleast 3 times
dialysate flow rate(25-30ml/min).
• Outflow dialysate is 100% saturated with urea
and other solutes at this rate.
• So urea clearance can be estimated by
effluent volume.

49. cont
• Standard QD – 26ml/min or 37L/day
• Excess fluid removed- 3L
• Daily effluent or urea clearance – 40L
• So Kt = 40L, if V of distribution urea = 40
• Kt/V = 1
• GFR calculation = 40000ml/ 1440 min=
27.7ml/min.

50. Solute clearance with C-HF
• Typically replacement fluid- 20-25ml/kg/hr.
• Outflow nearly 100% saturated with postdilution
mode.
• With pre dilution there is slight lowering of urea
concentration of UF(80-90% of corresponding plasma
value).
• BFR= 150ml/min, dilution = (25/175) ml= 14 %.
• If effluent volume is 40L, post dilution Kt=40
• Predilution Kt = 34(86% of 40).
• So Kt/V= 34/40 = 0.85
• GFR = (34000/1440) = 23.6ml/min.

51. Filtration fraction
• Calculated as (UF/ plasma flow rate)
• PFR= BFR × (1-HCT)
• BFR= 150ml/min, HCT = 35, PFR= 100ml/min
• UF rate- 25ml/min, then FF= 25/100= 25%
• Rule of thumb- keep FF at 25% or lower to
avoid overconcentration of rbcs,plasma
proteins in hemofilter.

52. Dosing of CRRT
• Effluent volume =20-25ml/kg/hr(KDIGO AKI
2012).
• No evidence that lower levels give worse
results.
• Few randomized studies show markedly
higher effluent volumes led to better
outcomes, but results not confirmed.
• RENAL & ATN study consider SUN <45mg/dl to
consider adequate CRRT dosing.

53. Nutrient Requirements in ARF
• Calories: 25-45 kcals/kg dry weight
• Protein: about 10-16 g amino acids lost per
day with CRRT
• Acute HD: 1.2-1.4 g/kg;
• Acute PD: 1.2- 1.5 g/kg;
• CRRT: 1.5-2.5 g/kg

54. Drug dosing in
CRRT
• C-HF is superior at removing middle and large
mol wt drugs because of convection.
• CVVH>CVVHDF>CVVHD
• GFR depends on effluent volume
• Each 10L of effluent volume is equivalent to
7ml/min of GFR.