Continuous Renal Replacement Therapy

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Continuous Renal
Replacement Therapy -CRRT
Classical ‘renal’ indications for starting renal
replacement therapy (RRT) are:

Rapidly rising serum urea and creatinine or the
development of uraemic complications

Hyperkalaemia unresponsive to medical
management

Severe metabolic acidosis

Diuretic resistant pulmonary oedema

Oliguria or anuria
‘Non renal’ indications for starting
RRT are:
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Management of fluid balance e.g. in
cardiac failure
Clearing of ingested toxins
Correction of electrolyte abnormalities
Removal of inflammatory mediators in
sepsis?
Rhabdomyolysis
Diffusion-
movement of solutes across a semi
permeable membrane through a concentration gradient
Good for smaller sized molecules
Convection- movement of fluid across a semi
permeable membrane creating a solute drag.
Good for smaller and middle sized molecules
When to start RRT
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Conventional starting criteria for RRT should be used
Treatment should be started before complications
develop- Earlier the better!
The rate of change of urea and creatinine is more
significant than their absolute levels, however in most
cases RRT should be started before urea is 20 – 30
mmol/L.
Initiation of RRT on the basis of fluid balance, urine
output, potassium level or degree of acidosis will be
dependent on the patient’s clinical condition.
What type of RRT

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SCUF
CVVH
CVVHDF
CVVHD
SLED(D)
Ultrafiltration-UF
CVVH
CVVHDF
a blood pump provides
solute removal by
diffusion and convection
simultaneously.
It offers high volume
ultrafiltration using
replacement fluid which
can be administered
pre-filter/ post-filter.
Simultaneously,
dialysate is pumped in
counter flow to blood.
CVVH v CVVHDF


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There is no evidence to suggest that CVVH is
superior to CVVHDF in terms of patient outcome
or renal outcome (or vice versa).
With CVVHDF -UF flow rates may be reduced
therefore larger molecule removal by convection
is decreased
If adequate UF rates cannot be achieved using
CVVH due to machine limitations, then CVVHDF
should be considered.
A predominantly convective mode of clearance
may be considered in severe sepsis
Solute clearance- depends on
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Blood flow
Recirculation
Membrane characteristics- type of filter
Filter clotting- aim for 85% of prescribed dose
Pre/post dilution
The removal of potassium, correction of acidosis
or the removal of fluid may have just as much of
an impact on patient outcome as solute
clearance.
Pre filter dilution
Post filter dilution
Ultrafiltration flow rates

Moves towards higher UF rates

Too low reduces clearance of solutes

Too high- affect membrane performance

Filtration fraction <25%
Ultrafiltration Rates

Ronco et al (2000) large prospective study
Suggestion that a higher level of solute clearance was
beneficial at higher UF rates. (35 mls/kg/hr)


American Acute Renal Failure Trials Network (ATN study,
2008), did not find any difference in survival, rate of
renal recovery or nonrenal organ failure in ‘intensive’
versus ‘less-intensive’ renal support.
The Australian/NZ RENAL study (Randomised Evaluation
of Normal vs. Augmented Level of renal replacement
therapy in ICU, 2009) compared 40 ml/kg/h to 25
ml/kg/h of ultrafiltrate production in CVVHDF. No
difference in terms of outcome.
Points for consideration
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Replacement fluid
Membrane
Anticoagulation
Flow rates- vascular access
Temperature management
Drug dose adjustment
Replacement fluid

Composition similar to normal serum electrolytes
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Bicarbonate/lactate buffer.

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The individual components of filtration fluid vary
but phosphate and potassium supplementation
is often needed.
Bicarbonate may trigger inflammatory
mediators, an undesirable side effect in the
critically ill and could theoretically be harmful.
Membranes
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High surface area
Used to be cellulose, now synthetic
biocompatable
Pore size affects solute transfer
Phosphates are lost at the same rate as urea
Doesn’t clear protein bound molecules eg
midazolam
Doesn’t secrete toxins like a tubular cell
Removes glucose
Future ? Bioartificial kidney with human tubular
cells lining hollow fibers
Anticoagulation
Anticoagulation
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No anticoagulation
UFH unfractioned heparin
LMWH low molecular weight heparinFragmin
Prostacyclin
Citrate
Others
No Anticoagulation
Increased risk of clotting
 Increased consumption of clotting factors and
platelets
 Short circuit life
Preventative Measures
 Pre-dilution
 High Flow
 Aim for Filtration fraction of 25% or less

Heparin

Occurs naturally in human mast cells within the
connective tissue of the blood vessels, liver and lungs.

Results seen instantly with a half-life of 30 minutes –
2hours

reversal with protamine sulphate but Fresh Frozen
Plasma remains the definitive treatment.

Heparin induced Thrombocytopaenia (HIT)
Keeling, D (2006) The management of heparin-induced thrombocytopenia British Society for Haematology 133: p259269
Heparin

Used in patients with normal coagulation profile, normal
platelet count and not at risk of bleeding

The most commonly used anticoagulation for CVVH.

Its cheap, effective and well tolerated.
APTT and platelet counts routinely measured
(no consensus on the frequency of testing -APTT does not
always reflect the anticoag effect of heparin)


(There is no correlation between increasing APTT and
filter life)
Fragmin

No evidence that it is superior to Unfractioned
heparin in terms of efficacy or risk of side effects

Extended half life

Less risk of HIT

lack of reliable predictors of bleeding and
antithrombotic activity
Epoprostenol (prostacyclin, Flolan®)

Considerable use in IHD and CVVH

Inhibits platelet aggregation

Can use in thrombocytopenia

50% reduction in bleeding therefore beneficial
with high risk of patients

Short half life of 3 minutes
IHD= intermittant haemodialysis
Epoprostenol (prostacyclin,
Flolan®)
Common concerns
 Expensive and has powerful vasodilator
properties
 Side effects of hypotension, flushing and
headache.
 There is no reliable laboratory test to quantify
the anticoagulation effect
 Its not effective for filter membrane fouling due
to fibre clotting
Citrate
Citrate binds with calcium and makes it
unavailable for clotting cascade so need to
-monitor serum calcium and give calcium infusion
-monitor sodium and acid-base status as citrate to
bicarbonate.
 Suggestion that citrate prolongs CRRT time and
reduces need for blood transfusions and/or
haemorrhage

Others
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Danaparoids; Fondaparinux- little experience of
use in CVVH; monitor anti Xa levels
Recombinant hirudin and argatroban are direct
thrombin inhibitors. Experience with these drugs
is limited, but increasing and they may have
pharmacological advantages.
Vascular access
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Usually double D or D/O x section
>11FG for blood flows >200-250ml/min
Polyurethane- 3 weeks
Jugular -Right side less recirculation
? subclavian
Femoral catheters shorter than 20cm
associated with increase recirculation
Hypothermia
Do the following have any place in preventing
hypothermia ?

Wrap circuit
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Fluid warmer
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Systemic warming
Hypothermia
Do the following have any place in
preventing hypothermia ?
Wrap circuit
NO
 Fluid warmer
NO
 Systemic warming
the only available option

Blood Requests

Due to the high volumes of filtration fluid
with the increased pump speed and UF
rates we need to monitor phosphate and
calcium daily
Bloods for U & E, FBC, Clotting- minimum
daily

TROUBLE SHOOTING

Connections top/bottom filter!
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Air detector
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Heparin infusion pump
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Vascular access
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Alarms
Thank You
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