1. Prescriptions in CRRT Timothy E Bunchman MD Professor & Director
Pediatric Nephrology

2. Factors effecting clearance in CRRT
BFR
Surface area of the membrane
Surface areas of the membrane usually correspond to the surface area of the child, yet there are limited options with most companies so many of us “make do”
Surface areas range from 0.1 to 1.6 M2
Convection vs Diffusion
Duration

3. Convective Clearance
To increase clearance by convection, increase ultrafiltration rate (will require more replacement fluids)

4. D
Diffusive Clearance
To increase clearance by diffusion, increase dialysate flow rate

5. Sieving Coefficients
Solute (MW) Convective Coefficient Diffusion Coefficient
Urea (60) 1.01 ± ± 0.07
Creatinine (113) 1.00 ± ± 0.06
Uric Acid (168) 1.01 ± ± 0.04*
Vancomycin (1448) 0.84 ± ± 0.04**
Calcium (protein bound)
Cytokines (large) adsorbed minimal clearance
*P< **P<0.01

6. Typical prescription for AKI
BFR 3-5 mls/kg/min
Surface area ~ to body surface area
Replacement or diffusive rate
at ~ 2000 mls/hr/1.73 M2 (Maxvold data)
35-45 mls/kg/hr (Ronco Lancet 2000 data)
Net ultrafiltration rates
Target similar to urine out put to mls/kg/hr but will be dictated by hemodynamics

7. Comparison of Urea Clearance: CVVH vs CVVHD (Maxvold et al, Crit Care med. 2000 Apr;28(4):1161-5)
p = NS
Urea Clearance
(mls/min/1.73 m2)
BFR = 4 mls/kg/min
FRF/Dx FR = 2 l/1.73 m2/hr
SAM = 0.3 m2

8. Indications for CRRT may effect decision making of the prescription
AKI with electrolyte disturbance the prescription above will work
But
What if the child is in state of hyper-metabolism then more may be needed
In born error of metabolism
Intoxications
Liver failure
Deep et al, Crit Care Med Oct;44(10):
What if the requirement is less
Hyperosmolar states

9. HD to Convective HF High Flux HD 8 liter CVVH Lithium 4 liter CVVH
mmol/l
4 liter CVVH
2 liter CVVH
Time

10. Ammonia Clearance HD Begins HF Ends HD Ends HF Begins at 8 l/hr
1800
HF Ends
HD Ends
1600
HF Begins at 8 l/hr
1400
1200
Ammonia (micromol/l)
1000
800
600
400
200 1 2 3 5 7 11 15 17 19
Time (hours)

11. Hyperosmolar state..less is better
Child with AKI with a
Serum glucose of 1300 mg/dl
BUN of 90 mg/dl
Na of 175 meq/dl (uncorrected)
Measured osmols of 482 mmol/l
An adjustment of the Na of the dialysate (we added 60 meq/l for a final Na bath of 200 meq/l)
An inefficient prescription is warranted to avoid a rapid shift in osmols
Frequent (? Q 2-4 hr) re evaluations and Na bath adjustments are needed

12. Time Hrs

13. Comparison of RRT modalities
Modality
CRRT
SLED
HD (standard or HF) PD
CFPD
BFR
3-5 mls/kg/min access dependent
10-20 mls/kg/pass
20-40 mls/kg/pass
Dialysis Flow Rate
0-4 liters/hr
6 liters /hr
30-50 liters/hr
0.5-2 liters/hr
Convective Flow Rate
Systemic Anticoagulation
Heparin or citrate
Heparin or none
none
Thermic control
Yes
yes
partial
Ultrafiltration control
Solutions
Industry made
On Line production
Drug clearance
Continuous
Intermittent
Nutritional clearance
Hemodynamic stability
(1 best; 4 least) 1 4 5 3 2
Solute clearance

14. Summary
The idea of “one size fits all” for a prescription is fraught with error for each indication may need some adjustment
Selecting a prescription for the indication at the beginning will allow for a more efficient mode or RRT with a benefit to the child