Renal replacement therapy Flashcards by Stephanie Saint Laurent

What are the indications for RRT?

-uremia
-volume overload
-metabolic acidosis
-hyperkalemia

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What is the mortality difference between IHD and CRRT?

none

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What is ultrafiltration?

movement of fluid across semipermeable membrane secondary to pressure gradient

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What is diffusion?

solute transport across a semipermeable membrane
-movement is concentration based
-best for small molecule clearance

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What is convection?

solute transport across a semipermeable membrane
-solute moves with solvent d/t transmembrane pressures
-removes broad spectrum of solute sizes

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Does CVVH use diffusion or convection to clear solutes?

convection

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What differentiates hemodialysis from hemofiltration?

-HD = removes solutes by diffusion; solutes diffuse down a concentration gradient
-HF = removes solutes by convection; solutes and water are pulled across a semipermeable membrane via pressure difference

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What size molecules is hemodialysis good for?

smaller molecules 10-100 kDa (i.e. creatinine and urea)

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What size molecules is hemofiltration good for?

middle sized molecules 10 - 10,000kDa

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What are the components of a CRRT prescription?

-modality
-blood flow rate
-replacement fluid rate
-type of replacement fluid
-how much UF to remove

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How do you calculate CRRT dose?

dose = replacement fluid rate / patient’s weight

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What is the recommend CRRT dose?

20 - 25 mL/kg/hr
-however surgical pts w/ frequent interruptions in the system it is good to target a dose of 25-30mL/kg/hr to make up for breaks

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What CRRT mode can be used to help pts w/ sepsis and AKI and why?

CVVH
-HF good for clearing medium sized molecules; inflammatory cytokines fit this category

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What factors increase risk of dialysis related hypotension?

-advanced age
-female
-hypotension prior to dialysis
-hypoalbuminemia
-higher BMI

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How do you calculate filtration fraction?

FF = replacement fluid + UF / blood flow rate + replacement fluid rate
-to minimize blood clot target a FF of < 25%

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What is the average increase in circuit life associated w/ use of citrate as anticoagulation for CRRT?

30hrs

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How is citrate metabolize? Into what

-hepatically metabolized
-into Ca and bicarb
-might need replacement fluids w/ lower bicarb to avoid metabolic alkalosis

How does toxicity d/t citrate manifest in pts w/ liver failure?

low serum ionized Ca

What is the total calcium : ionized calcium ratio indicative of citrate toxicity?

> 2.5

What is the recommended maximum prescription for net UF while on CRRT?

no to exceed 1.5 - 2mL/kg

What is the minimum blood flow rate needed to maximize clearance for prefilter replacement fluid rates of up to 1500mL/hr and dialysis fluid rates of up to 3600mL/hr?

150mL/min

Does iHD or CRRT tend to correct hyponatremia more quickly?

iHD

What makes up the total UF rate?

UF rate = (preblood pump/prefilter replacement fluid rate) + (postfilter replacement fluid rate)

What are the KDIGO guidelines for catheter sites to be used for CRRT?

RIJ
femoral
LIJ
try not to use subclavian

What are the KDIGO guidelines for length of catheters to use for CRRT?

-12 - 15cm for RIJ -19 - 24cm for femoral -15 - 20cm for LIJ recommend 11.5 - 14F catheters

What does the filtration fraction represent?

the fraction of plasma that is removed from the blood during hemofiltration

Which type of CRRT modes (convection versus diffusion) have higher filtration fractions?

convection

For convection modes what can be done to reduce filtration fraction and prolong hemofilter survival?

-using higher blood flow rates -predilution replacement fluids

What value of iCa indicates optimal regional AC when using citrate?

iCa < 0.35mmol/L

What did a meta-analysis show were the big differences between using citrate and heparin?

when using citrate see: -less risk of bleeding -prolonged filter life span -more episodes of hypocalcemia -no difference in mortality

What lab abnormalities indicate citrate excess?

-metabolic alkalosis -tot Ca/iCa < 2.5

How do you treat citrate excess?

-decrease blood flow rate -increase dialysate flow rate or decrease buffer concentration in other CRRT solutions

What lab abnormalities indicate citrate toxicity?

-anion gap metabolic acidosis -tot Ca/iCa > 2.5 -escalating Ca infusion rate

How do you manage citrate toxicity?

-decrease blood flow rate -increase dilaysate rate -discontinue citrate (can try one or two, don't necessarily need to do all 3)

What lab abnormalities are seen in citrate deficit?

-metabolic acidosis -tot Ca/iCa < 2.5

What blood flow rates should be used to limit the effects of citrate?

100 - 180mL/min

What 3 medication characteristics help predict if it will be removed by CRRT?

-volume of distribution (Vd) -molecular weight (MW) -protein binding

What Vd, protein binding, and MW predict that a drug will be removed by convection?

-low Vd < 2L/kg -low protein binding < 80% -small MW < 20,000Da (or at least smaller than the size of the filter pores)

What type of relationship does convective clearance have to replacement fluid?

positive linear relationship

What is the creatinine clearance of a UF of 2.5L/hr?

40mL/min (creat clearance = 2500mL/60min)

How much should the creatinine clearance increase per 0.5L/hr increase in convection?

10mL/min