Rrt

1. Renal Replacement Therapy
(RRT) in Critical Care
DR. NIDA

2. What is Renal Replacement Therapy
(RRT)?
 • Replaces kidney function to remove waste,
balance fluids and electrolytes
 • Used in ICU patients with acute kidney injury
(AKI)

4. Understanding Kidneys and Nephron
 • Kidneys filter ~180 liters of blood daily
 • Each kidney contains ~1 million nephrons
 • Nephrons include a glomerulus and renal
tubules
 • Functions: waste removal, fluid &
electrolyte balance, acid-base regulation

5. Indications of RRT
 1. Acute kidney injury (AKI) with:
 • Fluid overload (refractory to diuretics)
 • Hyperkalemia (K+ > 6.5)
 • Severe metabolic acidosis (pH < 7.1)
 • Rapidly climbing urea/creatinine (or urea >
30mmol.l-1)
 • Symptomatic uraemia: encephalopathy,
pericarditis, bleeding, nausea, pruritus
 • Oliguria/anuria.

6. Indications for RRT – AEIOU
 • A: Acidosis
 • E: Electrolyte imbalances (e.g.,
hyperkalemia)
 • I: Intoxications (e.g., lithium, methanol)
 • O: Overload (fluid not responsive to
diuretics)
 • U: Uremia (e.g., encephalopathy,
pericarditis)
 Severe sepsus

9. Acute renal failure, also known as
acute kidney injury (AKI)
 abrupt (within 48 hours) reduction in kidney
function. The AKI network defines the
reduction in kidney function as the presence
of any one of the following:
 • An absolute increase in serum creatinine of
≥ 0.3 mg.dl-1 (≥ 26.4 mcmol.l-1)
 • A percentage increase in serum creatinine
of ≥ 50% (1.5-fold from baseline)
 • A reduction in urine output (< 0.5 ml.kg-1 per
hour for more than six hours).

10. Modalities of RRT in ICU
 • Intermittent Hemodialysis (IHD)
 • Sustained Low-Efficiency Daily Dialysis
(SLEDD)
 • Continuous Renal Replacement Therapy
(CRRT): SCUF, CVVH, CVVHD, CVVHDF

13. HemoFiltration ( convection )
 Haemofiltration= blood being pumped through an extracorporeal
system
 semi-permeable membrane
 hydrostatic pressure created on the blood-side of the filter
 drives plasma water across the filter
 This process is referred to as ultrafiltration
 Molecules that are small enough to pass through the membrane
(<50,000 Daltons) are dragged across the membrane with
 the water by the process of convection.
 The filtered fluid (ultrafiltrate) is discarded
 replacement fluid is added in an adjustable fashion according to the
desired fluid balance.

14. Haemodialysis (diffusion)
 Haemodialysis involves blood being pumped through an extracorporeal
system that incorporates a dialyzer.
 In the dialyzer, blood is separated from a crystalloid solution (dialysate) by
a semi-permeable membrane.
 Solutes move across the membrane along their concentration gradient
from one compartment to the other obeying Fick`s laws of diffusion.
 For example, bicarbonate moves from dialysate to blood whereas urea and
potassium move from blood to dialysate.
 dialysate flows countercurrent to the flow of blood.
 When removal of water is required the pressure on the blood-side of the
membrane has to be increased forcing water molecules to pass into the
dialysate.

15. Haemodiafiltration
 a combination of filtration and dialysis.
 It has the benefits of both techniques

16. SCUF
 Slow continuous ultrafiltration is used when the only
requirement is water removal.
 Effectively, it is CVVH with a low filtration rate.
 It can remove up to 6 litres of fluid a day but solute
removal is minimal.

24. Replacement fluid
 It is a substitution fluid:
 A solution of variable composition
 physiologic
 used to replace large volumes of ultrafiltrate during hemofiltration or
hemodiafiltration.
 Replacement fluid may be given as predilution or postdilution."

25. Dilaysate
 A solution of variable composition designed to facilitate diffusion of solutes into
the ultrafiltrate-dialysate compartment of the hemofilter or hemodialyzer.“
 Dialysate is the fluid which is infused into the filter
 by convention everything that comes out of the filter is called effluent

27. Components of CRRT circuit

29. Intetmittent vs Continuous
 Dialysing with higher flow rates than CRRT.
 A typical regime is 3-5 hours of dialysis 3 times
a week.
 The high flow rates and rapid fall in plasma
osmolality mean that it is only suitable for
patients who are cardiovascularly stable.

30. Continuous mode of hemodialysis
 CRRT involves filtering and/or dialysing on a
continuous basis.
 It allows better fluid managemen.
 creates less haemodynamic disturbance
 more expensive than IHD and requires continuous
rather than intermittent coagulation.
 There is some evidence to suggest that CRRT is
superior to IHD in
 patients with sepsis, cardiovascular instability or with
a head injury.

31. SLED
 Sustained low efficiency dialysis is an
example of a hybrid therapy which aims to
combine the logistic and cost advantages of
IHD with the relative cardiovascular stability
of CRRT.
 Treatments are intermittent but usually daily
and with longer session durations than
conventional IHD
 Solute and fluid removal are slower than
IHD, but faster than CRRT

32. WHICH FORM OF RRT SHOULD WE US
 What we want to remove from the plasma
 The patient`s cardiovascular status
 The availability of resources
 The clinician`s experience
 Convective modes of RRT may be beneficial if the patient
has septic shock
 • CRRT can aid feeding regimes by improving fluid
management
 • CRRT may be associated with better cerebral perfusion
in patients with an acute brain injury
 or fulminant hepatic failure

34. Modality Comparison: IHD vs SLEDD
CRRT
 Duration: IHD (3–5 hrs)
 SLEDD (~12 hrs)
 CRRT (24 hrs)
 • Clearance: IHD > SLEDD > CRRT
 • Hemodynamic stability: CRRT > SLEDD > IHD

36. Continuous Renal Replacement
Therapy (CRRT)
 • Used for unstable ICU patients needing
slow, continuous therapy
 • SCUF: fluid removal only
 • CVVH: convection-based clearance with
replacement fluid
 • CVVHD: diffusion-based clearance with
dialysate
 • CVVHDF: combines convection and diffusion

37. Components of RRT Circuit
 • Blood pump
 dialyzer
 anticoagulant
 replacement fluid
 Pressures:
 blood flow (QB)
 dialysate flow (QD)
 TMP for ultrafiltration

38. Dialyzer Membranes and Performan
 • Synthetic membranes preferred over
cellulose for better biocompatibility
 • Factors: flux, permeability, surface area
 • Clears solutes based on size and
transport mechanism

39. Vascular Access for RRT
 • Preferred sites: Right IJV > Femoral >
Left IJV > Subclavian
 • Types:
 AV fistula
 tunneled catheter
 temporary catheter

40. Anticoagulation During RRT
 • Systemic: Heparin (risk of HIT, bleeding)
 • Regional: Citrate (preferred for
circuit longevity)
 • Citrate chelates calcium – monitor for
electrolyte shifts

45. Drug Dosing in CRRT
 • Affected by protein binding, volume of distribution, TMP
 • Beta-lactams: frequent dosing or infusion
 • Fluconazole: increased clearance
 • Vancomycin: monitor levels closely

47. When to Stop RRT
 • Urine output > 400 mL/day suggests
renal recovery
 • Creatinine clearance > 20 mL/min
often used as threshold
 • Monitor creatinine trend during
steady-state

48. Chronic Kidney Risk Post-AKI
 • 40% of ICU AKI survivors develop CKD
 • Some remain dialysis dependent
 • Follow-up nephrology care is essential

49. Research & Controversies in RRT
 • Timing of RRT initiation: early vs
delayed
 • High-volume haemofiltration in
sepsis: unclear benefit
 • Need for validated AKI biomarkers

50. Summary: Key Points in RRT
 • CRRT preferred in unstable patients
 • Know AEIOU indications
 • Tailor modality, dosing, and
anticoagulation to the patient
 • Watch for complications and long-term
kidney outcomes