CRRT solutions
Benan Bayrakci, 2014
CRRT delivery
• CVVH is convective, use replasment fluid ( lood side of the filter)
• CVVHD is diffusive, use dialysate fluid (opposite side of the filter)
• There are no convincing clinical data to support either CVVH or CVVHD
• Combination therapy; CVVHDF is also not supported by evidence
• How fluid is delivered has little impact on the composition of the fluid
• The replacement and dialysate fluids should have the same composition
to reduce staff confusion and the risk for error
Options for fluids in CRRT
• Custom fluids compounded by the pharmacy
- The complications of compounding include increased cost and a shorter shelf
life (usually 30 days).
• Commercially prepared fluids with additives
- K, P, Mg and even bicarb can be added as needed but, carries the
risque for pharmacy errors and may increase costs.
- Whether replacement fluid or dialysate is utilized, the fluid should be
ultrapure and sterile.
- Each time an additive is injected, this is associated with a chance of
human error; contamination; wrong dose; wrong syringe, wrong vial etc.
• Commercially prepared pre-mixed fluids
- The safest approach. Less expensive and have longer shelf life.
- Available from multiple manufacturers, generally 3 l and 5 l bags with a
discrete number of fluid compositions.
- The most common concentrations of these solutes are equal to normal
plasma levels
Evaluation of Errors in Preparation of CRRT Solutions
• Survey of 3 Pediatric Listserves:
– Pediatric Critical Care, Nephrology, CRRT
• 16/31 programs reported solution
compounding errors
• Consequences of improper solutions
– 2 deaths
– 1 non lethal cardiac arrest
– 6 seizures (hypo/hypernatremia)
– 7 without complications
Barletta et al, Pediatr Nephrol. 21(6):842-5, 2006 Jun
PD solutions are not recommended!
because of the risque of hyperglycemia and metabolic acidosis
Replacement fluids:
• Are directly given in to the blood pre- or post filter
• They are used to increase the amount of convective
solute removal
• Despite their name, replacement fluids do not
replace fluid.
• Fluid removal rates are calculated independently of
replacement fluid rates
Predilution:
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Lower solute clearance,
Higher ultrafiltration rate
Larger filter surface area
Reduced sludging and need for anticoagulation
Use of pre-filter replacement fluids invalidate post-filter lab
draws
Postdilution:
– Higher filtration fraction
Fluid Composition
Sodium
• Should be in the physiologic range (140 meq⁄l).
• Customization needed if hypertonic citrate for
anticoagulation is used
• CVVHDF is more likely to achieve serum sodium
concentrations within the normal range than CVVH
• Supraphysiological sodium concentration in the
dialysate or replacement solutions would improve the
hemodynamic stability or prevent the increase in
intracranial pressure, but there are no conclusive data
concerning this issue.
Potassium
• K concentrations between 0 to 4 meq⁄ l are
acceptable and commercially available.
• Most patients have a degree of hyperkalemia at
initiation of RRT therapy.
• If K free fluid is used, careful monitoring is necessary.
• In cases of severe hyperkalemia associated with
arrhythmia and⁄or hemodynamic collapse
hemodialysis should be utilized.
Calcium
• About 60% of total plasma calcium is ultrafilterable,
substitution fluid in CVVH must contain about 3 mEq/l
of calcium
• Patients undergoing an exchange of very large volumes
of ultrafiltrate carry the risk of hypercalcemia,
therefore may require a lower content of calcium in
replacement fluids.
• Calcium is always absent from solutions when
phosphate is present
• During citrate anticoagulation, if calcium is present in
the fluid it will neutralize the citrate before it can do its
job of keeping the filter free of clots
Magnesium
• Mg in CRRT fluids ranges between 1 and 1.5 meq ⁄ l.
This level is not well studied but has been clinically
successful
• A bolus of 2–4 g should be prescribed when Mg
levels fall below normal range.
Phosphorus
• P plays a key role in cellular metabolism and is essential in several
biological processes
• Phosphorus is not a standard component of replacement or
dialysate fluids in CRRT. This is appropriate as CRRT is commonly
employed in the setting of hyperphosphatemia
• Majority of patients on CRRT will require phosphate
supplementation shortly after CRRT initiation.
• Critically ill patients present several conditions predisposing
hypophosphatemia such as sepsis, malnutrition, catecholamines,
intravenous glucose infusion, hyperventilation, diuretics and
rhabdomyolysis.
• Management of hypophosphatemia:
- Ensure proper nutrition.
- Add P to the solutions
- Use Phosphate-containing ready solutions
The addition of phosphate to the CRRT fluids at concentrations of up to 7.7 mg/dL
does not cause problems with precipitation or instability of the mixture.
Glucose
• Physiologic concentrations of glucose in the dialysate
and replacement fluids is advised to compensate
extracorporeal losses
• Glucose-free solutions might be used when an
adequate nutritional regimen has been established
Lactate
• The simplest, most economical solution; no mixing required.
• Effectiveness is well-supported in clinical literature.
• Many adults are successfully treated with CVVH using Lactated
Ringer's solution as it is:
- convenient
- cheap
- eliminates risk of pharmacy error
• Patients with severe liver failure, and particularly those with
reduced muscle blood flow, may fail to metabolise lactate and
develop a metabolic acidosis.
• In ICU patients suffering from multiple organ dysfunction, the
conversion of lactate to bicarbonate is frequently impaired
• Lactic acidosis causes cardiac dysfunction and hypotension
• Many fluids contain a small, clinically insignificant amount of
lactate to improve stability
Sodium bicarbonate
• The sodium bicarbonate concentration in CRRT fluids can be
variable. With customized solutions bicarbonate theoretically
can vary from 0 to 150 meq ⁄ l.
• With prescribed CRRT clearances of 20 ml⁄kg⁄hour, most acid
base disturbances can be managed with commercially
available bicarbonate compositions of 25 meq⁄ l to 35 meq⁄ l.
• If there is difficulty improving pH with a commercially
available solution, therapy can be changed to accommodate
the patient’s needs.
– Options: Pharmacy customized solutions with higher bicarb
– Supplemental bicarbonate drip
– Increase the clearance rate of the CRRT system. By increasing the
clearance rate, acid removal is increased as is bicarbonate
administration.
– The first two options have a risk of human error, whereas it is
simple to increase clearances to significantly greater than 35 ml
⁄kg ⁄hour.
• Bicarb-buffered replacement fluids can improve acid-base
status and reduce cardiovascular events better than lactate
fluids
• The buffer concentration should exert a buffer load that may
compensate for deficits, for losses in the buffer process, and
for extracorporeal losses and should therefore usually be
supraphysiological.
• Be avare of hypercapnia!
• Citrate is metabolized to bicarbonate, each citrate ion
producing three bicarbonate ions, no additional anionic
base is required during citrate anticoagulation
• Bicarbonate-based dialysate/replacement fluids are
considered standard of care today
• Dialysate solutions containing bicarbonate have low
compatibility with calcium. If calcium is added to a bag
containing bicarbonate, calcium carbonate produces ,
which could precipitate out of solution and clog the
filter.
• Calcium can be added to bicarbonate-containing
solutions in limited amounts; calcium concentrations of
less than 2.5 mEq/L usually do not result in
precipitation.
• The two-compartment bag with unique peel-seam
interface simplifies preparation and mixing prior to
use.
• A total of 62 patients
• Bicarbonate-based CRRT fluids cost some 28% more than standard lactate fluids
• Bicarbonate fluids led to a more rapid fall in lactate and greater improvement in base
excess during CRRT, but not overall control of acidosis
• The choice of fluid for CRRT did not affect blood pressure or vasopressor requirements.
Albumin
Can be added in dialysate to remove protein bound
medications in the setting of intoxication as well as
substances such bilirubin
Fluid temperature
• The use of replacement fluids or dialysate solutions at room
temperature as well as continuous blood flow through the
extracorporeal system cause an average 2C reduction in body
temperature, and an energy loss of about 1,000 kcal/day
• The energy loss during CVVHD is important in hemodynamic
stability and prognosis
• Heat loss and consequent hypothermia may also affect immune
functions and increase the risk of clotting of circuit
• Lower body temperature may be desirable in patients with
excessive oxygen consumption and low systemic vascular
resistance
• It is not clearly known in which patients the net effect of CRRTinduced hypothermia is useful or harmful
Formula of an Ideal CRRT Solution
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Physiological
Reliable
Inexpensive
Easy to prepare
Simple to store
Quick to the bedside
Widely available
Fully compatible
Solution?
A successful CRRT program can only run on safe fluids !