CRRT

1. Presenter : Numan Shah
IPMS-KMU
Peshawar
Continuous Renal Replacement
Therapy

2. Continuous renal replacement
therapy
 Introduction
 It is estimated that a third of patients in the critical
care setting have an AKI and approximately 5%
will require renal replacement therapy .
 The hospital mortality in patients with an AKI
requiring CRRT is as high as 60%.
 No specific treatments have been shown to
reverse the course of AKI, so CRRT forms the
basis of further management

3. Definition
 Acute kidney injury (AKI), is defined as an 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:
 1. An absolute increase in serum creatinine of ≥
0.3 mg.dl
 2. A percentage increase in serum creatinine of ≥
50% (1.5-fold from baseline)
 3. A reduction in urine output (< 0.5 ml.kg -1 per
hour for more than six hours).

4. Principles of renal replacement
therapy
 Renal replacement always uses a semi
permeable membrane to achieve blood
purification.
 It can be intermittent or continuous, and can
involve any of
4 major transport mechanisms:
 Diffusion, convection, adsorption and
ultrafiltration.

5. Semipermeable Membranes
 Semipermeable membranes are the basis of all
blood purification therapies.
 They allow water and some solutes to pass
through the membrane, while cellular
components and other solutes remain behind.
 The water and solutes that pass through the
membrane are called ultrafiltrate.
 The membrane and its housing are referred to as
the filter.

6. Semipermeable Membranes
 The rate of ultrafiltration will depend upon the
pressures applied to the filter and on the rate at
which the blood passes through the filter.
 Higher pressures and faster flows increase the
rate of ultrafiltration.
 Lower pressures and slower flows decrease the
rate of ultrafiltration.

7. Diffusion
 Diffusion is the movement of a solute across a
membrane through a concentration gradient.
 For diffusion to occur, another fluid must flow on
the opposite side of the membrane.
 In blood purification this fluid is called dialysate.
 When solutes diffuse across a membrane they
always shift from an area of higher concentration
to an area of lower concentration until the solute
concentration on both sides of the membrane is
equal.

8. Convection
 Convection is the movement of solutes through a
membrane by the force of water.
 Convection is sometimes called “solvent drag”.
 Convection is able to move very large molecules
if the flow of water through the membrane is fast
enough.

9. Convection
 In CRRT this property is maximized by using
replacement fluids. Replacement fluids are
crystalloid fluids administered at a fast rate just
before or just after the blood enters the filter.
 The increased fluid flow rate across the filter
allows more molecules to be carried through to
the other side.
 So it is with convection; the faster the flow
through the membrane, the larger the molecules
that can be transported.

10. Adsorption
 Adsorption is the removal of solutes from the
blood because they cling(adhere) to the
membrane.
 The same is true in blood purification. High levels
of adsorption can cause filters to block and
become ineffective.

12. Basic terms of CRRT therapy
CRRT encompasses several therapeutic
modalities:
 Continuous Hemodialysis (C-HD)
 Continuous Hemofiltration (C-HF)
 Continuous Hemodiafiltration (C-HDF)
 Sustained low-efficiency dialysis (SLED)
 Slow Continuous Ultrafiltration (SCUF)
 Continuous VenoVenous Hemofiltration (CVVH)
 Continuous VenoVenous HemoDialysis (CVVHD)
 Continuous VenoVenous HemoDiaFiltration
(CVVHDF)

13. Continuous Hemodialysis (C-HD)
 In C-HD dialysis solution is passed through the
dialysate compartment of the filter continuously
and at a slow rate.
 In C-HD, diffusion is the primary method of solute
removal.
 The amount of fluid that must be ultrafiltered
across the membrane is low (3-6 L per day) and
is limited to excess fluid removal.

15. Continuous Hemofiltration (C-HF)
 In C-HF dialysis solution is not used. Instead, a
large volume (about 25-50 L per day) of
replacement fluid is infused into either the inflow
or the outflow blood line (predilution or
postdilution mode, respectively).
 With C-HF, the volume of fluid that is ultrafiltered
across the membrane is the sum of replacement
fluid and excess fluid removed, and is much
higher than with C-HD.

16. Continuous Hemodiafiltration
(C-HDF)
 This is simply a combination of C-HD and C-HF.
 Dialysis solution is used, and replacement fluid is also
infused into either the inflow or the outflow blood line.
 The daily volume of fluid that is ultrafiltered across the
membrane is equal to the replacement fluid infused
plus the net volume removed.
 Usually, the replacement fluid volume with C-HDF is
about half that used with C-HF, but the total effluent
volume (replacement fluid + dialysis solution + excess
fluid volume removed) with C-HDF is similar to that
with C-HF, where effluent volume is the sum of
replacement fluid and excess fluid volume only.

18. Slow continuous ultrafiltration
(SCUF)
 Setup is similar to that for C-HD and C-HF, but
neither dialysis solution nor replacement fluid is
used. Daily ultrafiltered fluid volume across the
membrane is low (3-6 L per day), similar to C-HD.

19. Sustained, low-efficiency dialysis
(SLED)
 SLED is a form of IHD using an extended (6-
to 10-hour) session length and reduced blood
and dialysate flow rates.
 Typically, blood flow rates (BFRs) are about
200 mL/min and dialysate flow rate is 100-300
mL/min.
 Regular hemodialysis equipment can be used
as long as low blood and dialysate flow rates
are supported; a software update may be
required with certain dialysis machines to
provide the lower rates.

20. Sustained, low-efficiency dialysis
(SLED)
 The same machine used for IHD during the day
often can be used for SLED during the night, and
hemodialysis staff can easily be trained to
perform SLED.
 SLED-F requires additional infusion of
replacement fluid unless replacement fluid can be
made from dialysis solution online by the dialysis
machine.

21. Clinical indications
Potential advantages of slow continuous
therapies
 Hemodynamically well tolerated; smaller change in
plasma osmolality.
 Better control of azotemia and electrolytes.
 Correct Acid-base balance.
Highly effective in removing fluid (post surgery,
pulmonary edema, ARDS).
 Facilitates administration of parenteral nutrition and
obligatory intravenous medications (i.e., pressor,
inotropic drugs) by creating unlimited “space” by virtue
of continuous ultrafiltration.
 Stable intracranial pressure.
 New user-friendly machines available.

22. Comparison of techniques

23. Complications common to CRRT
 1. Complications related to the vascath (including
line-related sepsis)
 2. Haemodynamic instability
 3. Air emboli
 4. Platelet consumption
 5. Blood loss
 6. Electrolyte imbalances
 7. Hypothermia
 8. Effects of anticoagulation (bleeding or specific
side-effects of the anticoagulant used e.g.
heparin induced thrombocytopenia).