Hemofiltration replacement therapy

Hemofiltration is a prominent feature of many continuous renal replacement therapies (Table 6.2). How-ever continuous hemodialysis can also be employed to accelerate solute removal (16). The contribution of both processes to extracorporeal drug clearance will be considered separately in the context of continuous renal replacement therapy. 

Some of the renal replacement therapies listed in Table 6.2 incorporate continuous hemodialysis or a combination of continuous hemofiltration and hemodialysis. Continuous hemodialysis differs importantly from conventional intermittent hemodialysis in that the flow rate of dialysate is much lower than is countercurrent blood flow through the dialyzer. As a result/ concentrations of many solutes in dialysate leaving the dialyzer (Cd) will have nearly equilibrated with their plasma concentrations in blood entering the dialyzer (Cp) (16/31). The extent to which this equilibration is complete is referred to as the dialysate saturation (Sd) and is calculated as the following ratio ... 

The pharmacokinetics of intravenous ciprofloxacin have been studied in intensive care unit patients during continuous venovenous hemofiltration (n — 5) or hemo-diafiltration (n — 5) (67). Ciprofloxacin clearance was not altered. A dosage of 400 mg/day was sufficient to maintain effective drug plasma concentrations in patients undergoing continuous renal replacement therapy. 

Renal replacement therapies are the most common nonpharma-cologic treatment that patients with ARF receive. Absolute indications for starting RRT in an ARF patient do not exist, but some general guidelines for therapy initiation do exist (Table 42-6). Renal replacement therapies come in two different forms, intermittent therapies like hemodialysis, and continuous RRTs like continuous hemofiltration or peritoneal dialysis. A more detailed explanation of these therapies appears in Chap. 45. The choice of whether continuous therapies or intermittent RRTs are used is a matter of debate and is usually determined by physician preference and the resources available at the hospital. 

Renal replacement therapy—Any form of dialysis or hemofiltration used to support patients without adequate kidney function. Goals of renal replacement therapy are to remove excess fluid remove waste products and toxins and control electrolyte concentrations. 

Indications for renal replacement therapy in the acute setting and for other disease processes are different from those for ESRD. A common mode of ESRD therapy in the outpatient setting is intermittent hemodialysis (IHD) where a patient receives intense treatment over the course of a few hours several times a week. Acute renal failure in the inpatient setting is often treated with continuous renal replacement therapy (CRRT), which is applied for the entire duration of the patient s clinical need and relies upon hemofiltration to a higher degree than IHD (Meyer, 2000). Other nonrenal indications for CRRT are based on the theoretical removal of inflammatory mediators or toxins and elimination of excess fluid (Schetz, 1999). These illnesses include sepsis and systemic inflammatory response syndrome, acute respiratory distress syndrome, congestive heart failure with volume overload, tumor lysis syndrome, crush injury, and genetic metabolic disturbances (Schetz, 1999). 

As of 1995, more than 30 different polymer blends were being used in the manufacture of membranes for hemodialysis and hemofiltration (Klinkmann and Vienken, 1995). The various membrane types used for renal replacement therapy can be divided into membranes derived from cellulose (83 percent of 1991 worldwide total) and from synthetic materials (the remaining 17 percent) (Klinkmann and Vienken, 1995). Synthetic membranes have been constructed from such materials as polyacrylonitrile (PAN), polysulfone, polyamide, polymethylmethacrylate, polycarbonate, and ethyl-vinylalchohol copolymer (Klinkmann and Vienken, 1995). In the United States, use of cellulosic materials for membrane construction predominates at around 95 percent of the total number of membranes used (Klinkmann and Vienken, 1995). 

Complications that occur during hemodialysis and hemofiltration can be divided into problems related to vascular access and those due to exposure of the blood to the exchange circuit Depending upon the method used, vascular access problems associated with renal replacement therapy are similar to those experienced in patients with vascular grafts or catheters and are covered in those respective sections. 

The simultaneous treatment of apheresis combined with hemodialysis is actually performed at clinical scene when the patient with end-stage kidney failure needs the additional treatment. There are some types of plasmapheresis (PP), low density lipoprotein-apheresis (LDL-A), and double filtration plasmapheresis (DFPP) for apheresis. There are hemodialysis (HD) and continuous hemofiltration (CHF) for renal replacement therapy (RRT). Although a lot of clinical studies based on the local experiences are reported, "the product liability" always exists meaning that manufactures do not ensure these approach to therapy. 

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