Continuous renal replacement therapy crrt

Introduction
CRRT is a newer mode of dialysis that has many similarities to
traditional hemodialysis.
CRRT is a continuous therapy, slower type of dialysis that puts less
stress on the heart, that is monitored by the critical care nurse, and
it may continue over many days.
Instead of doing it over four hours, CRRT is done 24 hours a day to slowly
and continuously clean out waste products and fluid from the patient.
It requires special anticoagulation to keep the dialysis circuit from
clotting.

Introduction
The preferred choice of dialysis for these critically ill patients
needing renal support and/or fluid management
It allows doctors to give patients the fluids, nutrition, antibiotics and
other medications they need without worrying about the
accumulation of waste products and fluid from the failing kidneys.
The venous blood is circulated through a highly porous hemofilter.
As with traditional hemodialysis, access and return of blood are
achieved through a large venous catheter (veno-venous)

Hemofilters
ST 60 Filter: membrane surface area 0.6 M2,
blood flow range 50-180 ml/min and priming
volume of 44 ml, requires 1 L of priming
solution
ST 100 Filter: membrane surface area of 1.0 M2,
blood flow range of 75-400 ml/min and priming
volume of 69 ml, requires 1 L of priming
solution
ST 150 Filter (standard size for CRRT in adults):
membrane surface area of 1.5 M2, blood flow
range of 100-450 ml/min and priming volume of
105 ml, requires 2 litres of priming solution

Definition of CRRT
 Continuous renal replacement therapy (CRRT) is a therapy indicated for
continuous solute removal and/or fluid removal in the critically ill
patient.
 It allows for slow and fluid removal that results in better hemodynamic
tolerance even in unstable patients with shock and severe fluid overload.
 This process can be applied to both adults and children.
 CRRT therapy indications may be renal, non-renal, or a combination of
both.

Classical renal’ indications for starting renal replacement
therapy (RRT) are:
Rapidly rising serum urea and creatinine or the development of uraemic
complications
Hemodynamic instability (cardiovascular)
Hyperkalaemia unresponsive to medical management
Severe metabolic acidosis (DKA, Severe dehydration. Poisoning by aspirin,
ethylene glycol (found in antifreeze), or methanol. (reduction in bicarbonate
(HCO3, -pH may be markedly low or slightly subnormal, paCO2↓ )
Severe fluid overload unresponsive to diuretics
Oliguria or anuria

Non renal indications for starting RRT are:
For patients in whom continuous removal of volume or toxic substance is
desirable ( as in septic shock , AMI , severe GI bleeding ,ARDS or
condition with or at risk for cerebral edema ….)
Pre- and post-cardiovascular surgery / coronary artery bypass graft
(CABG), Removal of inflammatory mediators in sepsis?
Intoxication (methylene glycol):toxic alcohol that is found in various
household and industrial agents

Non renal indications for starting RRT are:
 Rhabdomyolysis: serious syndrome due to a direct or indirect muscle injury → →
death of muscle fibers and release of their contents into the bloodstream. → → renal
failure.
 A crush injury (auto accident, fall, or building collapse)
 Long-lasting muscle compression (prolonged immobilization after a fall or lying
unconscious on a hard surface during illness or while under the influence of alcohol
or medication)
 Electrical shock injury, or third-degree burn
 Venom from a snake or insect bite
 Extreme muscle strain,
 heroin, cocaine or amphetamines
 A very high body temperature (hyperthermia) or heat stroke
 A metabolic disorder such as diabetic ketoacidosis
 Sepsis

The main advantage of CRRT over other types of renal
replacement therapies is which one of the following?
 Faster electrolyte normalization
 Superior fluid control
 Faster recovery from acute kidney injury
 Lower mortality rates

Principles of CRRT / solute management
Diffusion: the movement of solutes through a semi-permeable
membrane from an area of higher concentration to an area of lower
concentration
Good for smaller sized molecules

Solute clearance- depends on
 Blood flow
 Recirculation
 Membrane characteristics- type of filter
 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
 Decrease blood viscosity, reducing
clotting and → →aids in extending
the filter life
 Increases urea clearance by up to
20%

Post filter dilution
 Primarily replaces fluid and
electrolyte losses
 No solute dilution
 Post dilution concentrates the
blood in the filter → →
enhancing clearance.

Convection: movement of fluid across a semi permeable
membrane creating a solute drag.
Efficient for both larger and smaller molecules
(Plasma water moves along pressure gradients)

Principles of CRRT / fluid management
Ultrafiltration-UF
Plasma water with solutes is drawn from the patient‟s blood
across the semipermeable membrane in the filter
The effluent pump controls the ultrafiltration rate
automatically according to the set flow rates.

Continuous Renal Replacement Therapy (CRRT)
Modes
• SCUF- Slow Continuous Ultrafiltration
 Ultrafiltration
• CVVH- Continuous Veno-Venous Hemofiltration
 Convection
• CVVHD- Continuous Veno-Venous Hemodialysis
 Diffusion
• CVVHDF- Continuous Veno-Venous Hemodiafiltration
 Diffusion and Convection

Choice of mode
CVVH
35mls/kg/ho
ur
CVVH
35mls/kg/hour
•First choice for most
ICU admissions with
multi organ failure
•Septic shock/severe
sepsis
Fluid removal
only
•Recovering multi
organ failure but
ongoing need for
RRT
•AKI with high urea
(initial setting)
Critical
Care
Clinical
Guideline
SCUF
CVVHDF
35mls/kg/
hour
CVVH
25mls/kg/
hour
•Failure of CVVH
•Limited period of
time for therapy

SCUF-Ultrafiltration
Slow continuous ultrafiltration:
Main indication is fluid overload without uremia.
 Requires a blood and an effluent pump.
 The effluent pump forces plasma water and solutes across the membrane in
the filter
 No dialysate or replacement solution.
 Fluid removal up to 2 liters/hr can be achieved.
 Treatment of choice in patients with heart failure, Maintains
cardiovascular stability
 Best suited to severely hypervolemic patients (i.e. post open-heart surgery,
post resuscitation)
This transport mechanism is used in SCUF, CVVH, CVVHD, and CVVHDF.

Maximum Patient Fluid Removal Rate = 1000 ml/hr

CVVHD
• Continuous veno-venous hemodialysis
 Requires the use of blood, effluent and dialysis pumps.
 Replacement solution is not required.
 Plasma water and solutes are removed by diffusion and
ultrafiltration.
 Dialysate formulas should reflect normal plasma values to
achieve homeostasis
 Maximum Patient Fluid Removal Rate
1000 ml/hr

306100135
CVVHD
Return Pressure Air Detector
Return Clamp
Access Pressure
Blood Pump
Syringe Pump
Filter Pressure
Hemofilter
Patient
Effluent Pump
Dialysate Pump Pre Blood Pump
BLD
Effluent Pressure

CVVHDF
Continuous veno-venous hemodiafiltration
Requires the use of a blood, effluent, dialysate and replacement pumps.
Both dialysate and replacement solutions are used
.
Removal of small molecules by diffusion through the addition of dialysate solution.
Removal of middle to large molecules by convection through the addition of
replacement solution
Plasma water and solutes are removed by diffusion, convection and ultrafiltration.
Maximum Pt. fluid removal rate = 1000 ml/hr

CVVH
35mls/kg/hour
CVVHDF
35mls/kg/hour
•Consider break/termination of therapy if patient has good solute clearance,
normal pH, normal potassium and is euvolaemic/persistently passing
good urine volumes.
•Filters should be electively taken down where possible rather allowed to clot
(to minimise blood loss)
•All filters should be electively taken down after 72 hours and a fresh
circuit built.
•If therapy is terminated for 3 hours or more and the vascath remains in
situ it should be locked with Taurolock.
•The vascath should be removed as soon as it is no longer needed for
ongoing therapy.
SCUF
Critical
Care
Clinical
Guideline
Termination of therapy

Termination of therapy
In daily practice, CRRT is discontinued on an
individual basis:
 When urinary output increases
 or when the CRRT session ends and the attending
physician supposes that renal function will
recover because other organ functions improve

Anticoagulation for CRRT
No anticoagulation : Saline flushes
 ↓ filter life span
 trauma, surgery, liver failure, coagulopathy, head bleeding
Active or recent bleeding)
Systemic Anticoagulation: systemic heparin or others
use CRRT syringe, DVT ,PE, mechanical heart valve
Regional Anticoagulation: Regional heparinization
safe and effective
Heparin
Regional citrate

Standard Heparin
Typical regimen in CRRT :
Priming of the circuit ( 5000 IU / L )
Initial Heparin Bolus : 5 - 8 IU / kg
Infuse Heparin at : 5 to 12 IU / kg / hr
The activated clotting time (ACT) on
post filter : Adjust heparin rate to
keep ACT between 1.5 & 2.0 times
Advantages
 Easy to perform
 Inexpensive
Disadvantages
• Occasional Thrombocytopenia
Hemorrhagic Risk with Bleeding
patient

low molecular weight (LMW) heparin
Typical regimen in CRRT :
Priming of the circuit : 20 mg in 1 L
Maintenance dose : 10 to 40 mg q6 hrs
Advantages
Decreased Risk of Bleeding
Disadvantages
Expensive
With low doses frequent filter clotting

Regional Citrate Anticoagulation
Typical regimen :
Citrate anticoagulation is always regional
Citrate infusion (4%) at ml/hr initially
Special Dialysate at 1 liter170 /hr ( Na+ 117 , K+ 4 , Mg++ 1.5 ,
Cl- 121.5 , dextrose 0.5- 2.5% , no Ca++ , no base )
CaCL2 (0.75%) by central I.V at 40-60 ml/hr,
Maintain ionized Ca++ at 0.96- 1.20 mmol/L
NB: Citrate is converted into sodium bicarbonate (1mmol of
citrate is converted into 3mmol sodium bicarbonate)

Citrate
Advantages :
No Bleeding
No Thrombocytopenia
Improved Filter Life and
Efficacy
Disadvantages :
Complex for the set up
Ca++ monitoring needed
Occasional Alkalosis

Record I/O (To calculate hourly urine
output, multiply the patient’s weight by
0.5 mL/kg and BP q1hr
Patency of circuit
Hemodynamic stability
Level of consciousness
Acid/base balance
Electrolyte balance
Hematological status
Infection
Nutritional status
Air embolus
Blood flow rate
Ultrafiltration flow rate
Dialysate/replacement flow rate
Alarms and responses
Color of ultra-filtrate/filter blood
leak
Color of CRRT circuit
Warm dialysate to 37C
Nursing Care of a Patient on CRRT
The critical care nurse must continuously monitor the following
parameters during CRRT

General observations : In order to maintain the systems patency,
 hourly checks of the vascath site (looking for redness, oozing/bleeding and
pain)
 Dialysis lines and filter pressures, should be carried out.
 These checks give early warning of unwanted side effects such as
accidental disconnection, air in a line or premature clotting of the filter,
as well as signs of infection.
 Weigh the patient daily to assess fluid removal.

Patency of circuit
 Clotting in the circuit is a common complication of CRRT.
 Heparin is infused on a continuous basis into the arterial side of the
CRRT circuit (called the prefilter) immediately before blood enters the
hemofilter.
 Citrate anticoagulation: it’s infused either prefilter or as a replacement
solution
 Monitor for signs and symptoms of bleeding in the oral mucosa, gastric
aspirate, stool, and injection sites. Check coagulation studies regularly

Patency of circuit
 Monitor serum calcium and give calcium infusion
 continuous citrate infusion puts the patient at risk for
metabolic alkalosis. Be sure to monitor laboratory values
regularly for alkalosis
 Routinely monitor the patient’s complete blood counts to
check for unintended blood loss in case the CRRT circuit
suddenly clots

How do you manage a patient with worsening acidosis on
CRRT?
 Step 1:
 Increase bicarbonate in dialysate
 Standard is 22 mEq/L  can increase to 32 mEq/L
 Step 2:
 Can evaluate for citrate toxicity
 Discontinue citrate if needed
 Step 3:
 Replacement fluid default is NS @ 200 cc/hr
 Consider changing to Free water with 150 meQ/L of NaHCO3

Temperature
 Body temperature should be monitored every two hours, at least.
 CRRT patients will drop their temperature by at least 2 C despite the fact
dialysate fluid is run through a warmer prior to entering the filter. (we heat the
dialysate fluid to reduce the amount of heat lost).
 Heating lights or warmed blankets are an option, but care must be taken not to
cover the lines as this increases the risk of disconnection.
 If a patient receiving CRRT is pyrexial, then it is likely they have a systemic
infection, so WCC and Blood Cultures should be checked.
 The results of these checks will indicate the presence and type of infection,

Cardiovascular
 Continual cardiac monitoring is necessary because CRRT
effects cardiovascular function, as a rapid change in serum
electrolytes, such as potassium or magnesium, can cause
arrhythmias.
 Regular sampling of blood is required to monitor electrolyte and
acid-base imbalances, so treatment can be adjusted accordingly
and supplements administered if necessary. (Check BUN, Crea,
Na,K, Cl, aPPT q6hr for 1 day & then q8hr. Check Ca,P,Mg qd. to
assess CRRT efficacy)

Cardiovascular
 Accurate recording of fluid levels is important, to ensure that the
patient does not become hyper - or hypo-volaemic; the patient relies
on external forces to control their internal environment.
 A common problem when on CVVHDF is hypotension. To
maintain adequate blood pressure, inotropes may be used.
 The fluid balance in a patient receiving CRRT can be adjusted in
two ways. The first is by removing more or less fluid via CRRT; the
second is by administering more or less fluid intravenously. This
ensures there is an adequate central venous pressure to maintain
dialysis

Respiratory
• Dialysis can cause changes in a patients fluid balance, therefore it is
important to closely monitor:
 respiratory effort
 the use of accessory muscles, signs of tachyponea
 distress, fatigue and signs of infection (regular sputum samples sent
for culture).
• Such monitoring is essential to discover or prevent the development of
pulmonary oedema or pleural effusions.
•

Respiratory
 For patients that are requiring non invasive or invasive
ventilation there may be the need for an increase in Positive
End Expiratory Pressure (PEEP) or Pressure Support (PS)
requirements, as the recent acidosis or metabolic derangement
may have caused the patient to overuse respiratory muscles.
Use of PEEP and PS is ensures there is an adequate central
venous pressure to maintain dialysis

Position
 The vascath access sites commonly used via the subclavian or internal
jugular veins. This may create a problem with positioning the patient as
the line needs to remain patent at all times.
 Positioning the patient on the vascath side will often occlude the vascath
as the increased pressure causes the vascath to be advanced slightly.
 Patients still need to be turned at least every 2 hrs to maintain good skin
integrity.
 They are often at a higher risk of pressure ulcers due to their
compromised state.

Neurological
 Reduced levels of consciousness, increased restlessness, agitation
and aggression are indications of neurological status changes.
 These changes result from raised creatinine levels, slow excretion
of sedatives and levels of pain.

 Treatment of pain needs to be very carefully titrated to ensure that
the patient is pain-free but not over-sedated.

Nutrition
 Nutrition of the patient, especially if they are to be dialysed for a
prolonged period of time.
 Due to the increased metabolic rate of ill patients, many are not able to
absorb provided nutrients and this can lead to gut atrophy.
 The use of enteral feeding is beneficial, as the feed helps to line the gut,
protecting it from gastric acids.
 If the patient is able to eat normally then a dietician should be involved to
ensure that a correct balance of nutritious foods is supplied.
 If the patient is unable to tolerate enteral feeding, Total Parenteral
Nutrition (TPN) may be considered.

Psychosocial
 A dialysed patient will be concerned, and possibly anxious, about the
machine.
 The presence of uncontrolled pain will add to these fears, as will the
lack of control over what is happening to their body.
 Regular education of the patient and family is of utmost
importance. To achieve this, simple explanations of ARF and dialysis
are required. The inclusion of a social worker can be beneficial, as are
regular visits by family.
 An Occupational Therapist can assist in offering diversional therapy
activities.

Indwelling Catheter
The development of a urinary tract infection is a side effect of
anuria, as the lack of urine output allows microbes to travel up the
catheter.
The removal of the urinary catheter is advisable until the patient
recommences micturating.

One of the main complications of CRRT
Hypotension, which can be related to several distinct
mechanisms including
 Hypovolemia
 alteration of myocardial function
 cardiac arrhythmia

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