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What we will go over today:

Understand the physiologic differences betweenhemodialysis and hemofiltration

Understand what is CVVH, CVVHDF, PUF, SLED,

SCUF

Understand the elements of the dialysis prescription

Review clinical trials comparing different dialytic

modalities

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Hemodialysis vs

Hemofiltration

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Hemodialysis

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Hemodialysis

Diffusive clearance Removal of solutes depend on:

- concentration gradient

- size of molecule

- surface area of membrane

Highly efficient system for

removing urea

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Hemodialysis solute levelshave sawtoothed fluctuations

UREA

TIME

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Hemofiltration

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Hemofiltration

Convective clearance

Solute removal depends

on:

- ultrafiltration rate

- size of molecule

Exactly as shown, this is

called PUF (pureultrafiltration)

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Continuous therapies

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CVVH (Continuous Veno-venousHemofiltration)

post-dilution

pre-dilution

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CVVHDF (Continuous Veno-venous HemoDiafiltration)

Dialysate

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CVVH - solute levels areconstant

UREA

TIME

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The Equipment

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We have come a long way

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Our toys

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Dialyzers

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Dialyzers

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The Prescription

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The Prescription

Hemodialysis Blood speed (300-350ml/min)

Dialysate flow (500-800ml/min)

Time (3-4 hours)

Fluid out

Bath

- Na+

- K+

- Ca2+

- HCO3

-

CVVH Blood speed (150-250ml/min)

Replacement fluid (15-30ml/min)

- saline

- saline + bicarb

- saline + bicarb + K+

- Prismasate

Net UF rate (even, -50, -100)

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Theoretical advantages of CVVHover Hemodialysis

Hemodynamically better tolerated

Better control of electrolytes and urea clearance

Better middle molecule clearance Greater removal of excess fluid

Allow simultaneous administration of large fluid

volumes Ease of use

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Overcoming BP Instability onHemodialysis

Lower dialysate temperature (34-36)

Slower UF rate, longer dialysis time

Higher Na

+

bath Higher Ca2+ bath

Iso-volumetric connection

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Is CVVH better thanHemodialysis?

Meta-analysis 9 RCT

Continuous vs

Intermittent

N=1403

Mortality

Crit Care Med. 2008 Feb;36(2):610-7

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Common Complications ofHemodialysis

Hypotension (20-30%)

Cramps (5-20%)

Nausea + vomiting

Headache

Chest pain

Back pain

Itch

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Special Precautions aboutCVVH Treatment interruptions

Clotting risk

- systemic anticoagulation: heparin

- regional anticoagulation: sodium citrate Electrolyte imbalance

- K+, Mg2+, PO4

-

Amino acid losses Drug dose adjustments

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Hemodialysis CVVH

Mechanism Diffusion Convection

Treatment Intermittent Continuous

Solute clearance Small > Large Small Large

Dialyzer Large surface Smaller surface

Pump speeds High volume Low volume

Complications Hypotension Clotting

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What about SLED and SCUF ?

SLED sustained low efficiency dialysis

useful in unstable patients, CVVH not

available

SCUF slow continuous ultrafiltration

useful in CHF who are difficult to diurese

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More dialysis isbetter ?

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VA/NIH ARF Trial Network

N Engl J Med 359:7, July 3, 2008

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All Cause Mortality

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Subgroup analysis

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Summary

Hemodialysis and Hemofiltration have different

mechanisms in solute clearance

Hemofiltration (CVVH) has not been shown to

be superior to intermittent hemodialysis More intensive renal replacement therapy in

acute renal failure has not been shown to

improve survival

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Questions