Hemofilter
   HOME

TheInfoList



OR:

Hemofiltration, also haemofiltration, is a
renal replacement therapy Renal replacement therapy (RRT) is therapy that replaces the normal blood-filtering function of the kidneys. It is used when the kidneys are not working well, which is called kidney failure and includes acute kidney injury and chronic kidney dis ...
which is used in the
intensive care Intensive care medicine, usually called critical care medicine, is a medical specialty that deals with seriously or critically ill patients who have, are at risk of, or are recovering from conditions that may be life-threatening. It includes p ...
setting. It is usually used to treat
acute kidney injury Acute kidney injury (AKI), previously called acute renal failure (ARF), is a sudden decrease in renal function, kidney function that develops within seven days, as shown by an increase in serum creatinine or a decrease in urine output, or both. ...
(AKI), but may be of benefit in
multiple organ dysfunction syndrome Multiple organ dysfunction syndrome (MODS) is altered organ function in an acutely ill patient requiring immediate medical intervention. There are different stages of organ dysfunction for certain different organs, both in acute and in chronic ...
or
sepsis Sepsis is a potentially life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs. This initial stage of sepsis is followed by suppression of the immune system. Common signs and s ...
. During hemofiltration, a patient's
blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood is com ...
is passed through a set of tubing (a ''filtration circuit'') via a machine to a
semipermeable membrane Semipermeable membrane is a type of synthetic or biologic, polymeric membrane that allows certain molecules or ions to pass through it by osmosis. The rate of passage depends on the pressure, concentration, and temperature of the molecules o ...
(the ''filter'') where waste products and water (collectively called ''ultrafiltrate'') are removed by
convection Convection is single or Multiphase flow, multiphase fluid flow that occurs Spontaneous process, spontaneously through the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoy ...
. Replacement fluid is added and the blood is returned to the patient. As in
dialysis Dialysis may refer to: * Dialysis (chemistry), a process of separating molecules in solution **Electrodialysis, used to transport salt ions from one solution to another through an ion-exchange membrane under the influence of an applied electric po ...
, in hemofiltration one achieves movement of solutes across a
semi-permeable membrane Semipermeable membrane is a type of synthetic or biologic, polymeric membrane that allows certain molecules or ions to pass through it by osmosis. The rate of passage depends on the pressure, concentration, and temperature of the molecules o ...
. However, solute movement with hemofiltration is governed by convection rather than by diffusion. With hemofiltration, dialysate is not used. Instead, a positive
hydrostatic pressure Hydrostatics is the branch of fluid mechanics that studies fluids at hydrostatic equilibrium and "the pressure in a fluid or exerted by a fluid on an immersed body". The word "hydrostatics" is sometimes used to refer specifically to water and o ...
drives water and
solutes In chemistry, a solution is defined by IUPAC as "A liquid or solid phase containing more than one substance, when for convenience one (or more) substance, which is called the solvent, is treated differently from the other substances, which are ...
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 engendered by the hydrostatic pressure. Thus convection overcomes the reduced removal rate of larger solutes (due to their slow speed of diffusion) seen in hemodialysis.


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 Ultrafiltration (UF) is a variety of membrane filtration in which forces such as pressure or concentration gradients lead to a separation through a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained in t ...
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

These treatments can be given intermittently, or continuously. The latter is usually done in an intensive care unit setting. There may be little difference in clinical and health economic outcome between the two in the context of acute kidney failure.


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, had historically never been used in an outpatient setting in the United States.


Continuous hemofiltration or hemodiafiltration (CHDF)

Continuous hemofiltration (CHF) was first described in a 1977 paper by Kramer et al. as a treatment for fluid overload. Hemofiltration is most commonly used in an intensive care unit setting, where it is either given as 8- to 12-hour 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 A central venous catheter (CVC), also known as a central line (c-line), central venous line, or central venous access catheter, is a catheter placed into a large vein. It is a form of venous access. Placement of larger catheters in more centr ...
placed in one of the large central
veins Veins () are blood vessels in the circulatory system of humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are those of the pulmonary and fetal c ...
. In such cases a blood pump is used to drive blood flow through the filter. Native access for hemodialysis (e.g. AV fistulas or grafts) are unsuitable for CHF because the prolonged residence of the access needles required might damage such accesses. The length of time before the circuit clots and becomes unusable, often referred to as ''circuit life'', can vary depending on the medication used to keep blood from clotting.
Heparin Heparin, also known as unfractionated heparin (UFH), is a medication and naturally occurring glycosaminoglycan. Heparin is a blood anticoagulant that increases the activity of antithrombin. It is used in the treatment of myocardial infarction, ...
and regional
citrate Citric acid is an organic compound with the formula . It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry Biochemistry, or biological chemistry, is the study of chemical processes within and relati ...
are often used, though heparin carries a higher risk of bleeding. However, a comprehensive analysis of audit data from intensive care units in the UK revealed that, compared with heparin, citrate-based drugs were not associated with fewer deaths among patients with
acute kidney injury Acute kidney injury (AKI), previously called acute renal failure (ARF), is a sudden decrease in renal function, kidney function that develops within seven days, as shown by an increase in serum creatinine or a decrease in urine output, or both. ...
after 90 days of treatment. Citrate-based drugs were, however, associated with a substantially higher cost of treatment.


History of continuous renal replacement therapy

Before implementing continuous renal replacement therapy (CRRT), acute renal failure (ARF) in critically ill, multiple organ failure patients was managed by intermittent hemodialysis and the mortality rate was very high. Hemodialysis is effective in clearance and ultrafiltration, but it has deleterious effects on hemodynamic stability. In 1971, Lee Henderson described the basis for convective transport in blood purification techniques. Subsequently, in 1974 he described hemodiafiltration combining convection and diffusion. These seminal papers represented the basis for the development of chronic hemodiafiltration by Leber and continuous arteriovenous hemofiltration (CAVH) by Peter Kramer. With his team, Peter Kramer (Died unexpectedly in 1984), had actually first reported the use of continuous hemofiltration in Germany in 1977. Peter Kramer in ASAIO presented a paper describing the use of arteriovenous hemofiltration in the management of ARF. Kramer tried that as a mean of managing diuretic-resistant fluid overload. Kramer described his experience of attaching a microporous hemofilter to the femoral artery and vein, and flowing blood through it at around 100 ml/minute. Liters of plasma filtrate poured out. He replaced it with an infusion of electrolyte solution. Kramer explained that this could be done continuously, avoiding the volume shifts and other problems of intermittent hemodialysis. For those in the audience who cared for patients with anuric ARF, this was an epiphany of thunderbolt proportions. He used a hollow fiber “haemofilter” that originally designed as an alternative to HD for chronic renal failure and produced 300-600 ml/hour of ultrafiltrate by convection. The simple, pumpless system made use of temporary dialysis catheters sited in the patient’s femoral artery and vein and could be rapidly established in critically ill patients. Kramer explained that this could be done continuously, avoiding the volume shifts and other problems of intermittent hemodialysis. For those in the audience who cared for patients with anuric ARF, this was an epiphany of thunderbolt proportions. He used a hollow fiber “haemofilter” that originally designed as an alternative to HD for chronic renal failure and produced 300-600 ml/hour of ultrafiltrate by convection. The simple, pumpless system made use of temporary dialysis catheters sited in the patient’s femoral artery and vein and could be rapidly established in critically ill patients. Using an isotonic salt solution for fluid replacement, continuous arteriovenous hemofiltration (CAVH) was soon extended to the management of ARF. In 1982, Kramer presented his experience with its use in more than 150 intensive care patients at a meeting of the American Society for Artificial Internal Organs(ASAIO). Before that, Henderson et al and Knopp, had studied hemofiltration in animals and as an alternative to dialysis in chronic renal failure, but it was really Peter Kramer’s report in ASAIO meeting in 1982 that stimulated many of nephrologists and intensivists to undertake the serious evaluation of CAVH in ARF in the ICU. At first, in CAVH, the prescribed ultrafiltration rate was achieved manually by arranging the filtrate bag at the right height, thereby changing the negative pressure caused by the filtrate column. The replacement fluid was also regulated manually. Few years later, CAVH was developed in several centers for managing ARF in critically ill patients with multiple organ failure. In 1986, it has been reported that CAVH improve the patient survival from 9% to 38% with full nutrition in ARF. Moreover, a workshop presented at ASAIO in 1988 summarized the development and role of continuous hemofiltration. Since late 1980s, continuous renal replacement therapy (CRRT) has been studied extensively. In 1982, the use of CAVH in Vicenza was extended for the first time to a neonate with the application of specific minifilters . Two years later, CAVH began to be used to treat septic patients, burn patients and patients after transplantation and cardiac surgery, even with regional citrate anticoagulation. In 1986, the term continuous renal replacement therapy was applied to all these continuous approaches. The technology and terminology were expanded to include slow continuous ultrafiltration for fluid removal without replacement, continuous arteriovenous hemodialysis (CAVHD), and continuous arteriovenous hemodiafiltration. Meanwhile, clinical and technical limitations of CAVH spurred new research and the discovery of new treatments, leading to the development of continuous veno-venous hemofiltration (CVVH), continuous veno-venous hemodialysis (CVVHD) and continuous veno-venous hemodiafiltration (CVVHDF). The low depurative efficiency was overcome by applying filters with two ports in the dialysate/filtrate compartment and through the use of counter-current dialysate flow, allowing the addition of diffusion and the birth of continuous arteriovenous hemodiafiltration or hemodialysis (CAVHDF or CAVHD). Development of double-lumen venous catheters and peristaltic blood pumps was invented in the mid-1980s, when CVVH was proposed. The presence of a pump that generated negative pressure in part of the circuit made it necessary to add a device to detect the presence of air and a sensor to monitor the pressure in the circuit, to avoid, respectively, air embolisms and circuit explosion in case of coagulation or obstruction of the venous line. Later, ultrafiltrate and replacement pumps and a heater were added to the circuit. The development of CVVH allows to increase the exchange volumes, and subsequently, the depurative efficiency. The use of counter-current dialysate flow led to further improvements and the birth of CVVHD and CVVHDF. Now Continuous renal replacement therapy has become the mainstay of management of renal failure for multiple organ failure patients in the ICU. Information technology and precision medicine have recently furthered the evolution of CRRT, providing the possibility of collecting data in large databases and evaluating policies and practice patterns. The application of artificial intelligence and enhanced human intelligence programs to the analysis of big data has further moved the front of research ahead, providing the possibility of creating silica-trials and finding answers to patients’ unmet clinical needs. The opportunity to evaluate the endophenotype of the patient makes it possible to adjust treatments and techniques by implementing the concept of precision CRRT. This allows clinicians to normalize outcomes and results among different populations or individuals and establish optimal and personalized care


See also

*
Hemodialysis Hemodialysis, American and British English spelling differences#ae and oe, also spelled haemodialysis, or simply ''"'dialysis'"'', is a process of filtering the blood of a person whose kidneys are not working normally. This type of Kidney dialys ...
*
Renal replacement therapy Renal replacement therapy (RRT) is therapy that replaces the normal blood-filtering function of the kidneys. It is used when the kidneys are not working well, which is called kidney failure and includes acute kidney injury and chronic kidney dis ...
*
Extracorporeal An extracorporeal procedure is a medical procedure which is performed outside the body. Extracorporeal devices are the artificial organs that remain outside the body while treating a patient. Extracorporeal devices are useful in hemodialysis and ...
therapy


References

{{Urologic procedures Membrane technology Nephrology procedures Extracorporeal procedures