renal replacement therapy for pediatrics · practical considerations for crrt qb: the access issue...
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Renal Replacement Therapy For Pediatrics
Theory and Practice Eileen Tsai, MD
June 11, 2014
General Principals
Kids are NOT small adults!!! Unfortunately current day equipment is not
designed for children! Most of the CRRT theory and practice is similar
between adults and children
Overview
Peds vs Adults: Indications (Same) Transport mechanisms (Same) Available Modalities (Same) Dosing? (Same) Equipment (Same- unfortunately!)
Anti-coagulation Citrate (preferred in pediatrics) Heparin
CRRT Indications Acidosis (metabolic) Electrolytes- (severe refractory)
K, Ca, ?Phos Ingestions, Inborn error of metabolism Overload of Fluids
Increasing evidence that earlier is better 75% of our calls Is there a role for calculation of a fluid overload
index? Uremia
Encephalopathy, bleeding, pericarditis
Therapeutic Goals
Clearance- AEIU- describes the movement of solutes via diffusion, convection or a combination of the two
Ultrafiltration (UF)- O- describes the net removal of fluid (convection=fluid carrying solute)
Usually renal replacement therapy involves both processes
Therapeutic Goals
Remember that is most cases:
CRRT is supportive therapy Allows for:
Improved vent management Optimal nutrition +/- improved hemodynamics
Molecular Transport Mechanisms of Renal Replacement Therapy
Diffusion Convection/Ultrafiltration (Adsorption)
Diffusion vs. Convection C
lear
ance
Diffusive Clearance
Convective Clearance
Molecular Weight 100 1,000 10,000 10
CRRT Terminology
CVVH- Hemofiltration use of a hydrostatic pressure gradient to induce the filtration
(or convection) of plasma water across the membrane of the hemofilter
CVVHD- Hemodialysis transport process by which a solute passively diffuses down
its concentration gradient from one fluid compartment (either blood or dialysate) into the other
CVVHDF- Hemodiafiltration dialysis + filtration. Solute loss occurs by diffusion and convection
CRRT : Slow Continuous
Ultrafiltration (SCUF) Return
Effluent
Access
QUF (100-300 mL/hr)
Vol control, minimal solute clearance!! Ultrafiltration vol = Pt’s Wt loss
QB (50-100 mL/min)
CVVH : Continuous Hemofiltration
QUF (500-2000 mL/hr)
Return
Effluent
Access
Replacement QR
Predilution
Postdilution
Convective solute removal Clearance for all solutes =UF
QB (50-200 mL/min)
Return
Access CVVHD : Continuous Hemodialysis
Dialysate QDi
QDo
Diffusive solute removal Limited to small solute
QUF = Q Di – Q Do (100-300 mL/hr)
QB (50-200 mL/min)
Return
Access CVVHDF : Continuous Hemodiafiltration
Dialysate QDi
QDo
Replacement QR
Postdilution Convective + Diffusive solute removal Small to large molecules
Predilution
Effluent
Importance of Pediatric Access
Practical Considerations for CRRT QB: The access Issue
Equipment- Smaller vessels means small access smallest access is about an 7 to 8 french- extremely
difficult to place in anyone <3Kg Smaller access means:
Lower blood flows resistance to flow is ~ to the radius4- so blood flow is
generally limited by the size of access not necessarily what the patient “can provide”
Increased clotting!!!! Good news- CRRT is generally not QB limited
Practical Considerations for CRRT QB: The access Issue
Typical blood flow= BSAx100ml/min E.g. adult patient 1.73x100=170ml/min Baby 0.3m2= 30ml/min Lowest rate 10ml/min and the pump goes by 10s
Take home point- access is king and without you cannot successfully dialyze a patient
Practical Considerations for CRRT QB issues: <50 ml/min
Clinical Scenario I set the QB 30ml/min, machine is working. Uh-oh, access pressure is 0. What is an access disconnect alarm? The machine shut down.
How do I troubleshoot? 30 ml/min may not generate enough negative pressure
Target negative pressure -20 to -30
C-clamp goes between access and access pressure pod Too tight and access pressure skyrockets. This is bad… May be necessary on both access and return if CRRT is used
concurrently with ECMO
Practical Considerations for CRRT Prescription: Qd+Qr
What clearance do you prescribe? We generally aim for 2000-3000 ml/hr/1.73m2
Based on adult CVVH data How do we estimate clearance?
Predilution + dialysate rate (PrismaFlex) Dialysate rate (Next-stage)
E.g. Child with BSA of 1m2
Predilution of 400ml/hr Dialysate of 800ml/hr Clearance =1200ml/hr
UF of ~1-2cc/kg/hr (NET)
Practical Considerations for CRRT Solutions
Dialysate: Prismasate 4K/0Ca vs. 2K/0Ca Bicarbonate based- essentially lactate free
Predilution: Pharmacy made Varying degrees of buffer There are now commercially available pre-dilution
solutions approved for infusion Primasol Custom solution
Practical: Equipment We have to rely on equipment that is designed for adults- So
whats the big deal? Access and blood flows- this turns out not be such a big deal
except when Qb is limited to >50ml/min. Big problem is the total circuit volume Total circuit volume ~100cc Blood volume is ~80cc/kg
Adult- 80x60kg= ~5L Baby 80x3kg= 240ml Now lets put them on a circuit with a fill of 100cc! Add in hypotension and anemia Add in bradykinin release syndrome (some filter sets-AN69)
Initiation of CRRT
Optimization of Patient Hemodynamics:
Volume- want several 10cc/kg NS boluses available Pressors- start early Blood- in some circumstances needs to be hanging
Acid base status Bradykinin release syndrome AN69 membrane
(Prismaflex) More tolerated membrane polyarylethersulfone (PAES)
HF20, HF1000, HF1400 (Prismaflex) Not applicable to HF400 and HF700 (Next-stage)
Initiation of CRRT
Optimization of Machine Initial blood flows are as low as possible Often we will go up 10cc/min every 20 minutes
after patient is on Prime is occasionally with pRBCs, 5% albumin or
saline In extreme cases (smaller than 10kg) we may have
blood running into the patient or prime machine with blood
Ongoing Therapy
In smaller patients- errors are magnified Especially true with volume removal calculations
An adult may be able to tolerate a +/- 500ml fluid status In a small child this amount could mean room air and
intubation (or worse!)
Citrate Anti-coagulation: Mechanism
Ca is an essential cofactor for many of the cascade proteins
By removing the ionized Ca from blood; coagulation is prevented; i.e. banked blood
Desire a Post-filter iCa of around 0.4mmol/L which requires a citrate concentration of ~ 6mmol/L
The machine is anti-coagulated NOT the pt
Sites of Action of Citrate CONTACT PHASE
XII activation XI IX
TISSUE FACTOR TF:VIIa
THROMBIN
fibrinogen
prothrombin
Xa Va VIIIa Ca++ platelets
CLOT
monocytes / platelets / macrophages X
Phospholipid surface
CITRATE
Citrate in Practice
Citrate in Practice
Standardized Citrate ACD(A) Solution Citrate rate in ml/hr will be 1.5 x the BFR the
PRISMA machine at ml/min. (eg If BFR is 100ml/min, citrate is 150mls/hr)
Ca infusion (ie. 8gms Calcium Chloride in 1L NS, Calcium Gluconate is 16gms in 1L). This will run at 40% of the citrate flow rate. (eg citrate rate = 150 mls/hr then CaCl rate = 60 mls/hr)
Citrate Monitoring
2 hour after initiation of therapy and every 6 hours thereafter, send Post-filter ionized Ca (drawn from the return line,
blue sample port) Systemic ionized Ca (drawn from patient) along with
a total Ca
Citrate Complications
Citrate-induced hypocalcemia (Citrate Lock) If citrate is not effectively cleared (via dialysis or
hepatic metabolism) pts ionized Ca will drop while total rises; i.e. no longer regional
Hold ACD-A solution for several hours followed by adjustment of citrate infusion rate (70%)
Pts with hepatic dysfunction are at greatest risk
Citrate Complications
Citrate induced metabolic Alkalosis Citrate is metabolized to bicarb Original paper described several pts needing dilute
HCl infusion to correct resultant alkalosis Adjustment of predilution/dialysate, some centers
use a 22 meq/L Bicarb solution Adjustment of TPN acetate/Cl ratio
Take away point #1
You will always need to take into account the Citrate and Ca infusion rates when you make your UF calculations Total Fluid Removal Rate _____ml/hr=
Net UFR _____ml/hr + citrate rate _____ml/hr + CaCl rate ____ml/hr
So… for no UF at a BFR of 100 you need to remove 210ml/hr (3.5ml/min)
Take away point #2
Citrate is for the machine- so adjustments in the citrate rate are made to optimize iCa measurements from the blue port (think about where citrate enters)
Ca is for the patient- so adjustments in the Ca rate are made to optimize iCa measurements from the patient (think about where Ca enters)