Operational Characteristics

Kidney Function Restoration Program

Kidney Damage Homeopathic Remedies

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Anticoagulation

Surface

Surface

Trisodium Citrate Mechanism Crrt

Fibrin y

Fibrin

FIGURE 19-4

Pathways of thrombogenesis in extracorporeal circuits. (Modified from Lindhout [8]; with permission.)

Anticoagulation in Dialysis for ARF

Uremia \ /">C\ J Geometry Drug therapy ^—-V^ Manufacture

Dialyzer preparation Anticoagulation Blood flow access

Anticoagulation in Dialysis for ARF

Dialyzer preparation Anticoagulation Blood flow access

FIGURE 19-5

Factors influencing dialysis-related thrombogenicity. One of the major determinants of the efficacy of any dialysis procedure in acute renal failure (ARF) is the ability to maintain a functioning extracorporeal circuit. Anticoagulation becomes a key component in this regard and requires a balance between an appropriate level of anticoagulation to maintain patency of the circuit and prevention of complications. Figures 19-4 and 19-5 show the mechanisms of thrombus formation in an extracorporeal circuit and the interaction of various factors in this process. (From Ward [9]; with permission.)

Heparin CRRT Anticoagulant heparin (~400|x/h)

Arterial ter I

3-way stop cock

Replacement solutions

Dialysate 1.5% dianeal

Filter

"I

Ultrafiltrate (effluent dialysate plus net ultrafiltrate)

Venous

Citrate CRRT

Anticoagulant 4%% trisodium citrate (~170 mL/h)

Arterial

3-way stop cock

Dialysate NA 117, K4, Mg 1., Cl 122.5 mEq/L; dextrose 0.1%-2.5% Replacement zero alkali solution zero calcium 0.9%% saline (1000 mL/h)

Central

Filter

Ultrafiltrate (effluent dialysate plus net ultrafiltrate)

Venous

FIGURE 19-6

Modalities for anticoagulation for continuous renal replacement therapy. While systemic heparin is the anticoagulant most commonly used for dialysis, other modalities are available. The utilization of these modalities is largely influenced by prevailing local experience. Schematic diagrams for heparin, A, and citrate, B, anticoagulation techniques for continuous renal replacement therapy (CRRT). A schematic of heparin and regional citrate anticoagulation for CRRT techniques. Regional citrate anticoagulation minimizes the major complication of bleeding associated with heparin, but it requires monitoring of ionized calcium. It is now well-recognized that the longevity of pumped or nonpumped CRRT circuits is influenced by maintaining the filtration fraction at less than 20%. Nonpumped circuits (CAVH/HD/HDF) have a decrease in efficacy over time related to a decrease in blood flow (BFR), whereas in pumped circuits (CVVH/HD/HDF) blood flow is maintained; however, the constant pressure across the membrane results in a layer of protein forming over the membrance reducing its efficacy. This process is termed concentration repolarization [10]. CAVH/CVVH—continuous arteriovenous/venovenous hemofiltra-tion. (From Mehta RL, et al. [11]; with permission.)

Solute Removal

Membrane

Middle molecules

Small molecules-

Membrane

Middle molecules

Small molecules-

Diffusion

Dialysate

A

w

#

Concentration gradient based transfer. Small molecular weight substances (<500 Daltons) are transferred more rapidly.

Blood

Dialysate

m

■Vü.

r».

Convection

B

Movement of water across the membrane carries solute across the membrane. Middle molecules are removed more efficiently.

Concentration gradient based transfer. Small molecular weight substances (<500 Daltons) are transferred more rapidly.

Blood

Dialysate

«

* * * *

Adsorption

C

Several solutes are removed from circulation by adsorption to the membrane. This process is influenced by the membrane structure and charge.

FIGURE 19-7

Mechanisms of solute removal in dialysis. The success of any dialysis procedure depends on an understanding of the operational characteristics that are unique to these techniques and on appropriate use of specific components to deliver the therapy. Solute removal is achieved by diffusion (hemodialysis), A, convection (hemofiltration), B, or a combination of diffusion and convection (hemodiafiltration), C.

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