By C. Kliff. Stanford University.
However discount 100 mg zudena amex, unlike IHD cheap zudena 100mg amex, the dialysate flow rates are significant- ly slower than the blood flow rates (typical- FIGURE 19-8 ly, rates are 100 to 200 mL/min, dialysate Determ inants of solute rem oval in dialysis techniques for acute renal failure. Solute rem oval flow rates are 1 to 2 L/hr [17 to 34mL/min]), in these techniques is achieved by convection, diffusion, or a com bination of these two. As a consequence, dialysate flow on solute rem oval by solvent drag. As solute rem oval is solely dependent on convective rates become the limiting factor for solute clearance it can be enhanced only by increasing the volum e of ultrafiltrate produced. W hile removal and provide an opportunity for ultrafiltration requires fluid rem oval only, to prevent significant volum e loss and resulting clearance enhancement. Small molecules are hem odynam ic com prom ise, hem ofiltration necessitates partial or total replacem ent of the preferentially removed by these methods. Larger m olecules are rem oved m ore efficiently by this process and, thus, both diffusion and convection are used in m iddle m olecular clearances are superior. In interm ittent hem odialysis (IH D) ultrafiltration the same technique (hemodiafiltration, HDF) is achieved by m odifying the transm em brane pressure and generally does not contribute sig- both dialysate and a replacement solution nificantly to solute rem oval. In peritoneal dialysis (PD) the UF depends on the osm otic gra- are used and small and middle molecules can dient achieved by the concentration of dextrose solution (1. FIGURE 19-9 Dialyste flow,L/h Dialysis time Ultrafiltrate volume, Cycling M anual Com parison of weekly urea clearances with different dialysis tech- 1. Although continuous therapies are less efficient than inter- 40 48 352 20 15 m ittent techniques, overall clearances are higher as they are utilized Dialysate inflow, L/wk 160 96 continuously. It is also possible to increase clearances in continuous 302 techniques by adjustm ent of the ultrafiltration rate and dialysate 268 flow rate. In contrast, as interm ittent dialysis techniques are opera- tional at m axim um capability, it is difficult to enhance clearances except by increasing the size of the m em brane or the duration of 140 therapy. CAV/CVVH DF— continuous arteriovenous/venovenous hem odiafiltration; IH D— interm ittent hem odialysis; CAVH — con- 84 72 tinuous arteriovenous hem odialysis; PD— peritoneal dialysis. CAVHDF/CVVHDF IHD CAVH PD Supportive Therapies: Intermittent Hemodialysis, Continuous Renal Replacement Therapies, and Peritoneal Dialysis 19. Membrane clotting + +++ Duration +++ + FIGURE 19-11 Other factors Drug dosing in continuous renal replacem ent (CRRT) techniques. Nursing errors + +++ Drug rem oval in CRRT techniques is dependent upon the m olecular Interference + ++++ weight of the drug and the degree of protein binding. Drugs with significant protein binding are rem oved m inim ally. Aditionally, som e drugs m ay be rem oved by adsorption to the m em brane. M ost of the com m only used drugs require adjustm ents in dose to reflect FIGURE 19-10 the continuous rem oval in CRRT. The ability of each m odality to achieve a particular clearance is influenced by the dialysis prescription and the operational charac- teristics; however, it m ust be recognized that there m ay be a signifi- cant difference between the dialysis dose prescribed and that deliv- ered. In general, IH D techniques are lim ited by available tim e, and in catabolic patients it m ay not be possible to achieve a desired level of solute control even by m axim izing the operational characteristics. May require modular protein to meet protein requirements without carbohydrate overfeeding. Reassessment of requirements and efficacy of nutrition support Energy assessment W eekly HBE x AF x SF*, or Same Same indirect calorimetry Serum prealbumin Weekly Same Same Nitrogen balance Weekly Same Same * Harris Benedict equation multiplied by acimity and stress factors † Collect 24-hour urine for UUN if UOP ≥ 400 ml/d FIGURE 19-12 N utritional assessm ent and support with renal replacem ent tech- absorption occurs form the dialysate in hem odialysis and hem odi- niques. A key feature of dialysis support in acute renal failure is to afiltration m odalities and can result in hyperglycem ia. Interm ittent perm it an adequate am ount of nutrition to be delivered to the dialysis techniques are lim ited by tim e in their ability to allow patient. The m odality of dialysis and operational characteristics unlim ited nutritional support. In the presence of a OPERATING CHARACTERISTICS OF CRRT: failing kidney, fluid rem oval is often a chal- FLUID REM OVAL VERSUS FLUID REGULATION lenge that requires large doses of diuretics with a variable response.
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