MANAGEMENT OF
CONTINUOUS
HEMODIALYSIS
APACVS CONFERENCE.
July 12, 2013
Naveed Masani, MD
General Principles I
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Solute removal may be accomplished via
diffusion and/or convection
Hemodialysis involves diffusive clearance only –
two fluid compartments (patient’s blood and
dialysate) separated by a semi-permeable
membrane
Passive diffusion between the two
compartments of small molecules
General Principles II
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Blood and dialysate do not come into contact with each
other
Dialysate and blood run countercurrent in order to
maximize concentration gradients
Excellent small molecule clearance with HD over a
short period of time – i.e. potassium, creatinine, urea
The rapid rate of solute removal may result in abrupt
changes in osmolality resulting in fluid shifts and
hypotension
General Principles III
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Solute diffusion determined by concentration,
time, molecular size, and permeability + surface
area of dialyzer membrane
Where small molecules in high concentrations
require a short time, larger molecules in lower
concentrations require much longer times for
efficient removal
General Principles IV
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Where dialysis involves diffusion, hemofiltration
uses convective forces via solvent drag for
molecular clearance
Hemofiltration uses a hydrostatic pressure
gradient to move plasma water across the
membrane
Hemofiltration is optimal when fluid removal is
the primary goal, particularly in situations of
hemodynamic flux
Mechanisms I
Mechanisms II
Nomenclature
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SCUF - Slow Continuous UltraFiltration (slow
fluid removal) – fluid removal only; minimal
clearance
CVVH – Continuous Veno-Venous
Hemofiltration (convection)
CVVHD – Continuous Veno-Venous
HemoDialysis (diffusion)
CVVHDF – Continuous Veno-Venous
HemoDiaFiltration (convection + diffusion)
Nomenclature II
Technical Considerations
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Need for dual-lumen catheter access via femoral,
IJ, or subclavian approach
Requirement for separate Calcium/Magnesium
replacement via central line
Filter clotting frequency which often precludes
true “continuous therapy”
ICU care with one-to-one nursing
Frequent monitoring of electrolytes and acidbase status
Indications
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Hemodynamic instability
Hypercatabolic state
Nutritional demands
?Removal of Inflammatory Mediators in Sepsis
High-volume, daily intravenous requirements,
including pressors, anbx, blood products
Indications II
Anticoagulation I
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AC choice determined by patient needs, local expertise,
and ease of monitoring
Systemic Heparin
Regional Heparin with protamine reversal
LMWH
Regional Citrate – frequent monitoring of ionized
calcium, acid-base status
Saline Flushes
Prostacycline – platelet aggregation inhibition
Anticoagulation II
Outcomes I
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ARF occurs in 5% of hospitalized patients
Increased incidence in ICU patients – up to 40%
Mortality rate of 40% - 70%
Short term survival improved with dialysis,
though no change in overall mortality
Mortality dependent on underlying disease
Outcomes II
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Prospective study attempted to answer the
question of HD vs. Continuous therapy
146 patients with ARF requiring dialysis
randomized to intermittent vs. continuous
Despite “randomization”, two groups differed
significantly, with an increased severity of illness
and more disease in continuous group
Outcomes III
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PD vs CVVH studied in Vietnam – 70 patients
with ARF and sepsis – clear mortality benefit for
CRRT – 47% vs. 15%
Criteria for use of CRRT are varied
Use is increasing – Canadian study showed that
CRRT was used for 26% of all treatments for
ARF as opposed to 9% previously
It is unclear if CRRT improves outcomes
compared to intermittent therapy
Principles of Drug Dosing
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Drug removal affected by size, concentration,
distribution, and protein binding
Only the free, unbound portion of any drug is
available for removal
Protein binding is influenced by pH, presence of
uremic toxins, heparin, and concurrent
medications which displace drugs from their
binding sites
Sieving Coefficient
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Represents the ability of any particular solute to
cross a permeable membrane
SC of 0 indicates no drug removal; SC of 1
indicates removal at a rate of blood
concentration
Increased rate of ultrafiltration leads to increased
drug removal
Drug removal also affected by charge and ability
of membrane to bind the drug
Continuous vs. Intermittent
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Less frequency of hypotension with continuous
therapies
Continuous therapies allow for excess fluid
removal in hypotensive patients without an
increase in pressor requirements
Continuous solute clearance; no “saw-tooth”
pattern seen with intermittent HD
Per unit time, hemodialysis is more efficient at
small solute removal
Continuous vs. Intermittent
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Gentle fluid removal allows for “refill” time of
peripheral edema (approx. 10 cc/min)
Less complement activation with continuous
therapy
Less pulmonary leukostasis and capillary leak
with continuous therapy
CVVHDF road-map
replacement fluid
dialysate
~~~
ven <--
art -->
effluent ultrafiltrate