1. MANAGEMENT OF CONTINUOUS HEMODIALYSIS
APACVS CONFERENCE.
July 12, 2013
Naveed Masani, MD

2. General Principles I
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

3. General Principles II
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

4. General Principles III
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

5. General Principles IV
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

6. Mechanisms I

7. Mechanisms II

8. Nomenclature
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)

9. Nomenclature II

10. Technical Considerations
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 acid-base status

11. Indications Hemodynamic instability Hypercatabolic state
Nutritional demands
?Removal of Inflammatory Mediators in Sepsis
High-volume, daily intravenous requirements, including pressors, anbx, blood products

12. Indications II

13. Anticoagulation I
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

14. Anticoagulation II

15. Outcomes I 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

16. Outcomes II
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

17. Outcomes III
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

18. Principles of Drug Dosing
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

19. Sieving Coefficient
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

20. Continuous vs. Intermittent
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

21. Continuous vs. Intermittent
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

22. replacement fluid dialysate
CVVHDF road-map
replacement fluid dialysate
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effluent ultrafiltrate