Pediatric CRRT: The Basics Dialysis Prescription and Nutrition

1
Pediatric CRRT The Basics Dialysis Prescription
and Nutrition

• Peter Yorgin, MD
• Loma Linda University

2
(No Transcript)
3
Clearance

• Clearance UV/P
• Percent transferred across the membrane x flow
• K(CVVH) Qf (CDo /CBi )
• K(CVVHDF) QDi (CDo /C Bi ) Qf (CDo /CBi )
• CBi concentration in the inflow blood
  (prefilter) CBo concentration in the outflow
  blood (postfilter) Qf ultrafiltrate flow rate
  and CDo concentration in the dialysate
  outflow/ultrafiltrate QDi dialysate flow rate

4
Ultrafiltration-based clearance
Movement of water across a membrane in response
to a pressure gradient
LOW Pressure
HIGH Pressure
Semipermeable membrane
5
Diffusion-based clearance
Movement in response to a concentration gradient
Semipermeable membrane
6
In CRRT, UP

• UV/P
• For low molecular weight solutes, effluent (U)
  and plasma (P) are nearly equal so that they
  cancel each other out.
• Therefore, clearance is equal to the effluent
  volume.

7
The filtration spectrum
Molecular Weight
0 100 1000 10,0000 100,000
Electrolytes 1-80
Vitamin B12 1355
Interleukin 1 17-18,000
Urea 60.6
TNF ? 17,000
IL-6 26,000
Amino acids 75-204
Creatinine 113.12
Lipo-polysaccharides 5-25,000
Glucose 180
Shigatoxin 68,000
Vitamin C 176.13
Albumin 66,200
Molecular weight cut-off 20-30,000 da
8
How much ultrafiltration?

• UF rate of 1200 ml/m2/hr based on adult data.
• Sepsis, ARDS, possibly liver failure more (up
  to 4800 mL/m2/hr) may be better.
• UF limitations as a percent of blood flow
• UF equals Replacement fluid Patient fluid
  removal
• Lower risk of clotting lt20 UF/BFR
• Higher risk of clotting gt25 UF/BFR

9
Case Presentation

• A 27 kg female with Staph aureus sepsis is fluid
  overloaded, is intubated and has anuric acute
  renal failure which is unresponsive to diuretics.
  The PICU attending is eager to start CRRT so that
  a net -10 mL/hour can be removed.
• Her height is 129 cm. So BSA 0.98
• What is your dialysis prescription?

10
Dialysis prescription

• Desired clearance
• Blood flow rate
• Replacement fluid
• Patient fluid removal
• Dialysis fluid

11
Start with the blood flow

• BFR for CRRT
• 4-6 ml/kg/min
• 100 mL/m2/min
• Catheter dependent
• Maintain venous return pressure less than 200 mm
  Hg

12
How much clearance?

• Select optimal clearance (urea, creatinine)
• 50 ml/min/1.73 m2?
• 100 mL/min/1.73m2?
• Patient BSA x clearance (ml/min) x 60
  min/hour/1.73 total effluent needed per hour.

13
Determining how much effluent

• Body surface area (BSA)
• Wt (kg) x Ht (cm)/3600 0.98
• (Wt (kg) x 4) 7/ Wt (kg) 90 0.98
• (Patient BSA x clearance (ml/min/1.73m2) x 60 min
  /hour)/1.73 m2 total effluent needed per hour.
• For our patient (0.98 x 50 mL/min/1.73 m2 x 60
  min/hour)/1.73m2 1699 mL/hour

14
Calculating replacement fluid

• Patient fluid removal 300 mL/hour
• Citrate 180 mL/hr
• Calcium chloride 70 mL/hr
• IVF 40 mL/hr
• Net fluid removal 10 mL/hr

15
Calculating replacement fluid

• 20 limit with a blood flow rate of 100 mL/min
  1200 mL/hour
• If 25, replacement fluid 1500 mL/hour
• Subtract patient fluid removal (300 mL) 900
  mL/hour.
• Total UF 1200 mL/hour (1200 mL/m2)

16
Calculate dialysate

• If a total of 1699 mL/hour was needed to achieve
  a clearance of 50 mL/min/1.73m2
• Patient fluid removal 300 mL/hour
• Replacement fluid 900 mL/hour
• Dialysis fluid 500 mL/hour
• TOTAL 1700 mL/hour

17
Dialysis prescription
50 mL/min/1.73 m2

• Desired clearance
• Blood flow rate
• Replacement fluid
• Patient fluid removal
• Dialysis fluid

100 mL/min
900 mL/hour
300 mL/hour
500 mL/hour
18
The fellow tells you that he has optimized
clearance!

• The dialysate has been increased to 2500 mL/hour.
• He calculates total clearance to be 3700 mL/hour
  108.9 mL/min/1.73 m2
• Is this possible?

19
Nitty gritty points

• You can never clear more solute than there is
  solute flowing through the hemofilter.
• Red blood cells cannot (should not) be cleared.
• The solutes in the replacement fluid, citrate and
  calcium chloride generally do not need to be
  removed (ie creatinine, TNF? , etc).

20
Calculating the plasma flow rate

• Thus, maximum clearance is limited to the plasma
  flow rate through the hemofilter. If the
  patients hematocrit is 41, then 59 of the
  blood is plasma.
• The blood flow rate is 100 mL/min or 6000
  mL/hour.
• The plasma flow rate is 3540 ml/hr. The maximum
  clearance is limited to 104.2 mL/min/1.73 m2.
• But what about dilution with replacement fluids,
  citrate and calcium chloride/heparin?

21
Dilution and other things

• Dilution of the plasma with fluids, decrases the
  clearances
• Probably by 10-15
• There is some clearance due to the binding of
  larger solutes with the hemofilter membrane
  particularly during the first hour.
• Clearance differs relative to the molecular
  weight, protein binding and even the charge of
  the solute

22
Sieving coefficients
Teraoka S, et al. ASAIO 46 448-451, 2000.
23
Nutritional considerations
Molecular Weight
0 100 1000 10,0000 100,000
Electrolytes 1-80
Vitamin B12 1355
Interleukin 1 17-18,000
Urea 60.6
TNF ? 17,000
IL-6 26,000
Amino acids 75-204
Creatinine 113.12
Lipo-polysaccharides 5-25,000
Glucose 180
Shigatoxin 68,000
Vitamin C 176.13
Albumin 66,200
24
Amino acid losses

• 6 pediatric patients
• Prospective crossover design
• Caloric intake 20-30 above engery expenditure.
• Protein 1.5 g/kg/day
• 2 L/hr/1.73 m2 of dialysate or filtered
  replacement fluid
• Amino acid clearances were greater on CVVH than
  CVVHD
• Amino acid loss on CVVH and CVVHD was similar
  (12.50 1.29 g/day/1.73 m2 vs. 11.61 1.86
  g/day/1.73 m2), representing 12 and 11,
  respectively, of the daily protein intake.

Maxvold NJ, et al. Critical Care Medicine 28
(4)l161-1165, 2000
25
(No Transcript)
26
(No Transcript)
27
(No Transcript)
28
Thanks!