Hemofiltration 2554138 212175846 2008-05-13T19:14:30Z Epbr123 1395162 Reverted edits by [[Special:Contributions/216.115.125.141|216.115.125.141]] ([[User talk:216.115.125.141|talk]]) to last version by Quale In [[medicine]], '''hemofiltration''', also '''haemofiltration''', is a [[renal replacement therapy]] similar to [[hemodialysis]] which is used almost exclusively in the [[intensive care]] setting. Thus, it is almost always used for [[acute renal failure]]. It is a ''slow continuous'' therapy in which sessions usually last between 12 to 24 hours and are usually performed daily. During hemofiltration, a patient's [[blood]] is passed through a set of tubing (a ''filtration circuit'') via a machine to a [[semipermeable membrane]] (the ''filter'') where waste products and water are removed. Replacement fluid is added and the blood is returned to the patient. ==The Principle of Hemofiltration== As in [[dialysis]], in hemofiltration one achieves movement of solutes across a [[semi-permeable membrane]]. However, solute movement with hemofiltration is governed by convection rather than by diffusion. With hemofiltration, dialysate is not used. Instead, a positive [[hydrostatic pressure]] drives water and [[solutes]] across the filter membrane from the blood compartment to the filtrate compartment, from which it is drained. Solutes, both small and large, get dragged through the membrane at a similar rate by the flow of water that has been engineered by the hydrostatic pressure. So convection overcomes the reduced removal rate of larger solutes (due to their slow speed of diffusion) seen in hemodialysis. ==Replacement fluid composition== An [[isotonic]] replacement fluid is added to the blood to replace fluid volume and [[electrolytes]]. The replacement fluid must be of high purity, because it is infused directly into the blood line of the extracorporeal circuit. The replacement hemofiltration fluid usually contains [[lactic acid|lactate]] or acetate as a bicarbonate-generating base, or bicarbonate itself. Use of lactate can occasionally be problematic in patients with [[lactic acidosis]] or with severe liver disease, because in such cases the conversion of lactate to bicarbonate can be impaired. In such patients use of [[bicarbonate]] as a base is preferred.. ==Hemodiafiltration== Hemofiltration is sometimes used in combination with hemodialysis, when it is termed [[hemodiafiltration]]. Blood is pumped through the blood compartment of a high flux dialyzer, and a high rate of ultrafiltration is used, so there is a high rate of movement of water and solutes from blood to dialysate that must be replaced by substitution fluid that is infused directly into the blood line. However, dialysis solution is also run through the dialysate compartment of the dialyzer. The combination is theoretically useful because it results in good removal of both large and small molecular weight solutes. ==Intermittent vs. continuous modes of therapy== These treatments can be given intermittently, or continuously. The latter is usually done in an intensive care unit setting. ===On-line intermittent hemofiltration (IHF) or hemodiafiltration (IHDF) === Either of these treatments can be given in outpatient dialysis units, three or more times a week, usually 3-5 hours per treatment. IHDF is used almost exclusively, with only a few centers using IHF. With both IHF or IHDF, the substitution fluid is prepared on-line from dialysis solution by running dialysis solution through a set of two membranes to purify it before infusing it directly into the blood line. In the United States, regulatory agencies have not yet approved on-line creation of substitution fluid because of concerns about its purity. For this reason, hemodiafiltration is almost never used in an outpatient setting in the United States as of 2007. Use of sterile, pre-packaged substitution fluid would be cost-prohibitive in the current economic environment. ===Continuous hemofiltration (CHF) or hemodiafiltration (CHDF) === Hemofiltration is most commonly used in an intensive care unit setting, where it is either given as 8-12 hours treatments, so called SLEF (slow extended hemofiltration), or as CHF (continuous hemofiltration also sometimes called continuous veno-venous hemofiltration (CVVH)) or Continuous Renal Replacement Therapy (CRRT). Hemodiafiltration (SLED-F or CHDF or CVVHDF) also is widely used in this fashion. In the United States, the substitution fluid used in CHF or CHDF is commercially prepared, prepackaged, and sterile (or sometimes is prepared in the local hospital pharmacy), avoiding regulatory issues of on-line creation of replacement fluid from dialysis solution. With slow continuous therapies, the blood flow rates are usually in the range of 100-200 ml/min, and access is usually achieved through a [[central venous catheter]] placed in one of the large central [[veins]]. In such cases a blood pump is used to drive blood flow through the filter. Native access for hemodialysis (eg [[AV fistulas]] or grafts) are unsuitable for CHF because the prolonged residence of the access needles required might damage such accesses. ==Is on-line intermittent hemodiafiltration (IHDF) better than regular hemodialysis? == There is current controversy about whether intermittent on-line hemodiafiltration (IHDF) gives better results than hemodialysis in an outpatient setting. In Europe, several observational studies have compared outcomes in patients getting dialysis with those getting IHDF. These have suggested a lower mortality rate and other favorable outcomes in patients getting IHDF vs. those getting ordinary hemodialysis. <ref>Canaud B, Bragg-Gresham JL, Marshall MR, Desmeules S, Gillespie BW, Depner T, Klassen P, Port FK. Mortality risk for patients receiving IHDF versus hemodialysis: European results from the DOPPS. Kidney Int. 2006 Jun;69(11):2087-93. PMID 16641921</ref> However, the issue is not settled at this time, because the required randomized controlled clinical trials have not been done. Another problem has been that in several of the trials done, IHDF was compared to dialysis using low-flux (small pore) membranes, and the benefit found may have been due more to the use of a high-flux membrane than to the addition of convective transport (filtration) to dialysis. A recent Cochrane database review <ref>Rabindranath KS, Strippoli GF, Daly C, Roderick PJ, Wallace S, MacLeod AM. Haemodiafiltration, haemofiltration and haemodialysis for end-stage kidney disease. Cochrane Database Syst Rev. 2006 Oct 18;(4):CD006258. Review. PMID 17054289</ref> of available trials could not find a definite benefit of either IHF or IHDF vs. hemodialysis in terms of outcomes. ==References== <references/> ==See also== * [[Hemodialysis]] * [[Renal replacement therapy]] * [[Extracorporeal]] therapy ==External links== * http://vam.anest.ufl.edu/dialysis/ A free interactive simulation of a CVVH machine {{Vascular surgery procedures}} [[Category:Medical treatments]] [[Category:Nephrology]] [[es:Hemofiltración]] [[fr:Hémofiltration]]