Hemodialysis 1

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HEMODIALYSIS1.IntroductionIn medicine, hemodialysis (also haemodialysis) is a method that is used to achieve the extracorporeal removal of waste products such ascreatinine and urea and free water from the blood when the kidneys are in a state of renal failure. Hemodialysis is one of three renal replacement therapies (the other two being renal transplant and peritoneal dialysis). An alternative method for extracorporal separation of blood components such as plasma or cells is apheresis. Hemodialysis can be an outpatient or inpatient therapy. Routine hemodialysis is conducted in a dialysis outpatient facility, either a purpose built room in a hospital or a dedicated, stand alone clinic. Less frequently hemodialysis is done at home. Dialysis treatments in a clinic are initiated and managed by specialized staff made up of nurses and technicians; dialysis treatments at home can be self initiated and managed or done jointly with the assistance of a trained helper who is usually a family member. Hemodialysis is prescribed by physicians for patients with acute or chronic renal failure, when conservative therapy is judged inadequate. Dialysis therapy may be intermittent or continuous.

2.Need of machine2.1 Dialysis can do some of the tasks of healthy kidneys :Dialysis can remove waste products (e.g. urea, creatinine, phosphorus etc.). It remove excess water and Correct high or imbalanced levels of potassium, chloride, sodium, etc. in the blood. Dialysis can't automatically regulate blood pressure, Produce hormones like Erythropoetin (EPO), Regulate normal calcium levels.

2.2 Removing excess water :Hemodialysis will get rid of extra fluid in the blood through a process called ultrafiltration. How much fluid needs to be removed during each treatment is very important. To remove excess water, the dialysis machine puts pressure on the blood side of the semi permeable membrane in the dialyzer. This pressure forces salt and water out of the blood and into the dialysate. The used dialysate with the blood wastes and excess fluid is taken away and drained.

2.3 Electrolyte balance:When you have kidney disease some of the molecules in your body are out of balance. For example, you will have too many of some molecules like potassium, and bicarbonate. These types of molecules are called electrolytes and are important to the function of the heart and the nervous system. Too many or too few of these molecules can be bad for your heart, and other parts of body. During hemodialysis, the molecular imbalance in your body can be corrected

by adding some electrolytes to your dialysate solution while excess electrolytes are removed as part of your treatment. The goal is to get the right amount of the right electrolytes.

2.4 Function of machine:The hemodialysis machine is designed to provide hemodialysis treatment by controlling and monitoring both the dialysate and extracorporeal blood circuits. In the extracorporeal blood circuit, the blood is continuously circulated from the patient through a dialyzer, where toxins are filtered out through a semi-permeable membrane, before being returned to the patient. During this process, the extracorporeal blood circuit is monitored for venous and arterial blood pressures, and for the presence of air and blood. In the dialysate circuit, the dialysate concentrates are mixed with purified water, heated, degassed, and delivered to the dialyzer. Balancing chambers ensure that the incoming flow of the dialysate is volumetrically equal to the outgoing flow in order to control ultrafiltration from the patient.

3.PrincipleThe principle of hemodialysis involves diffusion of solutes across a semipermeable membrane. Hemodialysis utilizes counter current flow, where the dialysate is flowing in the opposite direction to blood flow in the extracorporeal circuit. Counter-current flow maintains the concentration gradient across the membrane at a maximum and increases the efficiency of the dialysis. Fluid removal (ultrafiltration) is achieved by altering the hydrostatic pressure of the dialysate compartment, causing free water and some dissolved solutes to move across the membrane along a created pressure gradient. The dialysis solution that is used may be a sterilized solution of mineral ions or comply with British Pharmacopoeia. Urea and other waste products, potassium, and phosphate diffuse into the dialysis solution. However, concentrations of sodium and chloride are similar to those of normal plasma to prevent loss. Sodium bicarbonate is added in a higher concentration than plasma to correct blood acidity. A small amount of glucose is also commonly used. Hemodialysis, which means cleaning the blood, is a treatment for people whose kidneys have failed. The hemodialysis process involves blood passing through a dialyzer (an artificial kidney) to remove wastes and excess water. The dialyzer uses tiny hollow filters that look like microscopic straws. The semi-permeable membrane surrounding these tubes is very thin and allows only some particles to pass through. As blood moves through these tubes it comes into contact with a solution called dialysate, a liquid made from water, an acid solution and a bicarbonate solution. The dialysate liquid is circulated around the outside of the hollow fibers.

The dialysis process causes molecules to move across the semi-permeable membrane of the dialyzer. As a result, some waste products and electrolytes in the blood will move from the blood side of the membrane into the dialysate solution and some molecules will move from the

dialysate side of the membrane into the blood. This process is called diffusion. Making tea offers an everyday example of diffusion. Putting a tea bag into hot water causes the bag to act like a semi-permeable membrane. The tea leaves are too big to get out of the bag but the flavour and colour of the tea is able to pass through the membrane into the water, while water is also able to pass through the membrane into the tea bag. During hemodialysis, large molecules such as blood cells and protein are kept inside the membrane but smaller molecules such as urea and creatinine (and other biological wastes) pass through the small holes of the dialyzers filters into the dialysate solution. 4. idea of design The hemodialysis machine pumps the patient's blood and the dialysate through the dialyzer. The newest dialysis machines on the market are highly computerized and continuously monitor an array of safety-critical parameters, including blood and dialysate flow rates; dialysis solution conductivity, temperature, and pH; and analysis of the dialysate for evidence of blood leakage or presence of air. Any reading that is out of normal range triggers an audible alarm to alert the patient-care technician who is monitoring the patient. Manufacturers of dialysis machines include companies such as Nipro, Fresenius, Gambro, Baxter, B. Braun, NxStage and Bellco. 4.1 Membrane flux and outcome Whether using a high-flux dialyzer improves patient outcomes is somewhat controversial, but several important studies have suggested that it has clinical benefits. The NIH-funded HEMO trial compared survival and hospitalizations in patients randomized to dialysis with either low-flux or high-flux membranes. Although the primary outcome (all-cause mortality) did not reach statistical significance in the group randomized to use high-flux membranes, several secondary outcomes were better in the high-flux group. A recent Cochrane analysis concluded that benefit of membrane choice on outcomes has not yet been demonstrated. A collaborative randomized trial from Europe, the MPO (Membrane Permeabilities Outcomes) study, comparing mortality in patients just starting dialysis using either high-flux or low-flux membranes, found a nonsignificant trend to improved survival in those using high-flux membranes, and a survival benefit in patients with lower serum albumin levels or in diabetics. 4.2 Membrane flux and beta-2-microglobulin amyloidosis High-flux dialysis membranes and/or intermittent on-line hemodiafiltration (IHDF) may also be beneficial in reducing complications of beta-2-microglobulin accumulation. Because beta2-microglobulin is a large molecule, with a molecular weight of about 11,600 daltons, it does not pass at all through low-flux dialysis membranes. Beta-2-M is removed with high-flux dialysis, but is removed even more efficiently with IHDF. After several years (usually at least 5-7), patients on hemodialysis begin to develop complications from beta-2-M accumulation, including carpal tunnel syndrome, bone cysts, and deposits of this amyloid in joints and other tissues. Beta-2-M amyloidosis can cause very serious complications, including spondyloarthropathy, and often is associated with shoulder joint problems.

Observational studies from Europe and Japan have suggested that using high-flux membranes in dialysis mode, or IHDF, reduces beta-2-M complications in comparison to regular dialysis using a low-flux membrane. 4.3 Dialyzer size and efficiency Dialyzers come in many different sizes. A larger dialyzer with a larger membrane area (A) will usually remove more solutes than a smaller dialyzer, especially at high blood flow rates. This also depends on the membrane permeability coefficient K0 for the solute in question. So dialyzer efficiency is usually expressed as the K0A - the product of permeability coefficient and area. Most dialyzers have membrane surface areas of 0.8 to 2.2 square meters, and values of K0A ranging from about 500 to 1500 mL/min. K0A, expressed in mL/min, can be thought of as the maximum clearance of a dialyzer at very high blood and dialysate flow rates. 4.4 Water system An extensive water purification system is absolutely critical for hemodialysis. Since dialysis patients are exposed to vast quantities of water, which is mixed with dialysate concentrate to form the dialysate, even trace minera