HEMODIALYSIS

1.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 machine

2.1 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 elec-trolytes 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 dialyzer’s 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 beta-2-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 mineral contaminants or bacterial endotoxins can filter into the patient's blood. Because the damaged kidneys cannot perform their intended function of removing impurities, ions introduced into the bloodstream via water can build up to hazardous levels, causing numerous symptoms or death. Aluminum, chloramine, fluoride, copper, and zinc, as well as bacterial fragments and endotoxins, have all caused problems in this regard.

For this reason, water used in hemodialysis is carefully purified before use. Initially it is filtered and temperature-adjusted and its pH is corrected by adding an acid or base. Then it is softened. Next the water is run through a tank containing activated charcoal to adsorb organic contaminants. Primary purification is then done by forcing water through a membrane with very tiny pores, a so-called reverse osmosis membrane. This lets the water pass, but holds back even very small solutes such as electrolytes. Final removal of leftover electrolytes is done by passing the water through a tank with ion-exchange resins, which remove any leftover anions or cations and replace them with hydroxyl and hydrogen molecules, respectively, leaving ultrapure water.

Even this degree of water purification may be insufficient. The trend lately is to pass this final purified water (after mixing with dialysate concentrate) through a dialyzer membrane. This provides another layer of protection by removing impurities, especially those of bacterial origin, that may have accumulated in the water after its passage through the original water purification system.

Once purified water is mixed with dialysate concentrate, its conductivity increases, since water that contains charged ions conducts electricity. During dialysis, the conductivity of dialysis solution is continuously monitored to ensure that the water and dialysate concentrate are being mixed in the proper proportions. Both excessively concentrated dialysis solution and excessively dilute solution can cause severe clinical problems.

4.5 Dialyzer

The dialyzer is the piece of equipment that actually filters the blood. Almost all dialyzers in use today are of the hollow-fiber variety. A cylindrical bundle of hollow fibers, whose walls are composed of semi-permeable membrane, is anchored at each end into potting compound

(a sort of glue). This assembly is then put into a clear plastic cylindrical shell with four openings. One opening or blood port at each end of the cylinder communicates with each end of the bundle of hollow fibers. This forms the "blood compartment" of the dialyzer. Two other ports are cut into the side of the cylinder. These communicate with the space around the hollow fibers, the "dialysate compartment." Blood is pumped via the blood ports through this bundle of very thin capillary-like tubes, and the dialysate is pumped through the space surrounding the fibers. Pressure gradients are applied when necessary to move fluid from the blood to the dialysate compartment.

5. Organisation of machine:

The 2008T hemodialysis machine is designed for functional efficiency. The back of the machine houses the utility connections such as water source, drain, and electrical connections. By mounting them to the back, the water lines and power cord remain out of the way during treatment.

The front of the machine contains all of the controls the operator needs access to during hemodialysis. It can be broken down into three main sections. The top section contains the control panel and houses the computer that runs the treatment program. The middle section contains the modules used for the safe transmission of the blood to and from the dialyzer. Dialysate is the primary concern of the bottom section of the 2008T hemodialysis machine. Here the concentrates used to make up the dialysate are mixed and pumped to the dialyzer.

The following pages contain front and rear views of the 2008T hemodialysis machine and a brief description of the machine’s features. You should familiarize yourself with the location and purpose of these features.

5.1 design consideration

A Dialysis Machine is an artificial kidney that treats the blood or persons with inadequate kidney function. Dialysis Machines are processor based pieces of equipment incorporating electromechanically controlled extracorporeal blood paths that leverage pumps and semi permeable dialyzer membranes to filter the patient’s blood. From an operational perspective, dialysis equipment need to meet specific safety criteria, one of which is single-fault tolerance. This means that no single point of failure in the pumps, motors, tubes, or electronics will endanger the patient or expose them to a hazardous condition. This means that there will be several redundant components and circuits, as well as "watchdog" managed disengage mechanisms in the system. These devices may include both active and passive components such as Control devices, sensors, motors, heaters, pumps, and valve drivers. Often a "Safe Mode" of operation would mean disabling the Arterial blood pump and clamping the venous line to prevent unsafe blood from flowing to the patient.

5.2 Parts:

5.2.1 The Arterial Drip Chamber Module

The arterial drip chamber module is a panel with guides for blood tubing and a holder for the arterial drip chamber. The button used to raise the arterial drip chamber level is located on the Blood Pump module.

5.2.2 The Blood Pump Module

The blood pump draws blood from the patient and pumps it to the dialyzer and back to the patient in a closed circuit. To accomplish this, the pump segment of the blood tubing is threaded through the pump housing along a circular track. As the pump rotor rotates, twin rollers squeeze the pump segment, pulling and pushing the blood through the blood pump segment. The speed of the pump can be adjusted using the arrow keys on the blood pump or the Blood Pump Rate button on the “Home” screen (see page 61 for more information). The blood pump can be stopped by pressing the Start/Stop key or by opening the blood pump door. When the door is open, the diameter of the pump segment is shown in the display window.

Pressing the single key on the Blood Pump Module activates a small pump that raises the fluid level in the arterial chamber. This key (level adjust) can be used only to raise the level of blood in the chamber, and cannot be used to lower it. This is to avoid introducing air into the blood flow.

The following table describes the operational features of the blood pump.

5.2.3 The Heparin Pump Module

The heparin pump provides a means of injecting heparin into the blood circuit gradually over the course of the treatment and/or as a bolus. The pump can accommodate a variety of syringes that are commercially available. The pump works in conjunction with the “Heparin” screen where such parameters as the size and type of the syringe, infusion rate, infusion time, and bolus amount of heparin to be infused are selected.

If heparin is infused manually (by pushing in the carriage lock button while pushing on the slide carriage), the volume will not be added to the displayed amount, and must be added to the total heparin amount. Manually moving the carriage to infuse heparin is not recommended.

5.2.4 The Level Detector Module

The Level detector module is used to monitor the level of fluid in the venous drip chamber. The venous drip chamber is mounted inside its holder and the blood tubing leading back to the patient is threaded through the venous line clamp below it. An ultrasonic device inside the chamber holder monitors the drip chamber for the presence of air. If the level of blood in the chamber is too low and air is detected, the machine alarms, the blood pumps stops, and the clamp occludes the venous blood tubing.

An optical sensor located below the occlusion clamp recognizes whether or not blood, an opaque fluid, is detected in the venous line. When the dialysate supply lines are on the shunt, and the shunt door is closed, and blood is not sensed, the audible alarm is suppressed entirely.

Also located on the front of the module is a pressure port. The small monitor line from the drip chamber is connected to the transducer port. The pressure of the venous side of the blood circuit is read by the transducer mounted on the inside of the module, and the pressure is displayed in the “Home” screen.

5.2.5 Blood Tubing System

The dialysate delivery machine can be used with a variety of blood-tubing configurations. The modules (Blood Pump, Level Detector, and Heparin Pump) can be arranged on the 2008T hemodialysis machine in a variety of ways to allow for pre- or post-arterial pump pressure monitoring. The machine can accommodate most standard blood tubing that have pump segments ranging from 2 to 10 mm internal diameter. An additional single needle blood pump and special arterial line with two pump segments and a compliance chamber is required on a machine set up for single-needle dialysis.

5.2.6 Dialyzer

The 2008T hemodialysis machine is compatible with commercially available dialyzers that are equipped with standard dialysate connections (ISO 8637 DIN 13090 part 3).

5.2.7 Blood Pressure Module

The Blood Pressure module is located internally with the pressure tubing running from the back of the machine to the cuff. The module can automatically take the patient’s blood pressure at defined intervals, record the systolic, diastolic, MAP, and pulse values, and plot out the results on both the “Blood Pressure” screen and the “Trends” screen. The pressure cuffs come in a variety of sizes to accommodate small through large adult patients. The Adult size comes standard with the 2008T hemodialysis machine and can accommodate patients with upper arm circumferences of 25-35 centimeters. An optional large cuff is also available.

5.2.8 The Shunt Interlock

The shunt interlock is located on the right side of the 2008T hemodialysis machine. It links the dialysate lines when they are connected to it. The shunt door flips up to reveal colorcoded latching-connectors.

Push the dialyzer connectors onto the shunt interlock to snap them in place

Press down on the end of the red or blue lever and pull out the dialyzer connector to remove it from the shunt interlock

The dialyzer connectors attach to the dialyzer during dialysis or the shunt interlock during rinse programs. Make certain to correctly match red to red and blue to blue.

The blue dialyzer supply line features a dialysate flow indicator tube. A moving float in the tube allows the operator to see when dialysate is running through the lines and the dialyzer. The float does not move when the machine

is in bypass.

The dialysate sample port on the same line allows the operator to take a sample of the dialysate.

Figure 13 - Shunt Interlock, Flow Indicator & Dialyzer Connectors (viewed from back of machine)

5.2.9 The Electrolyte Constituents

The acid concentrate is the major source of electrolytes in the dialysate. Increasing the Na+ concentration in the dialysate, therefore, increases the amount of acid concentrate.

Increasing the amount of acid concentrate also increases the concentration of the other electrolytic constituents. These changes can be observed in the electrolyte constituents shown in the left side of the “SVS Profile” subscreen.

To observe the electrolyte constituents for the higher concentration of sodium, select Start Na+. The values in the left column change to reflect the increased sodium (see Figure 33 on page 68). Select Base Na+ to observe the constituents at the base concentration. The

arrow indicates which of the Na+ concentrations corresponds to the values. If neither button is highlighted, the electrolyte constituents values defaults to the Base Na+ setting, as indicated by the arrow.

5.2.10 Catheter

Catheter access, sometimes called a CVC (Central Venous Catheter), consists of a plastic catheter with two lumens (or occasionally two separate catheters) which is inserted into a large vein (usually the vena cava, via the internal jugular vein or the femoral vein) to allow large flows of blood to be withdrawn from one lumen, to enter the dialysis circuit, and to be returned via the other lumen. However, blood flow is almost always less than that of a well functioning fistula or graft.

Catheters are usually found in two general varieties, tunnelled and non-tunnelled.

Non-tunnelled catheter access is for short-term access (up to about 10 days, but often for one dialysis session only), and the catheter emerges from the skin at the site of entry into the vein.

Tunnelled catheter access involves a longer catheter, which is tunnelled under the skin from the point of insertion in the vein to an exit site some distance away. It is usually placed in the internal jugular vein in the neck and the exit site is usually on the chest wall. The tunnel acts as a barrier to invading microbes, and as such, tunnelled catheters are designed for short- to medium-term access (weeks to months only), because infection is still a frequent problem.

Aside from infection, venous stenosis is another serious problem with catheter access. The catheter is a foreign body in the vein and often provokes an inflammatory reaction in the vein wall. This results in scarring and narrowing of the vein, often to the point of occlusion. This can cause problems with severe venous congestion in the area drained by the vein and may also render the vein, and the veins drained by it, useless for creating a fistula or graft at a later date. Patients on long-term hemodialysis can literally 'run out' of access, so this can be a fatal problem.

Catheter access is usually used for rapid access for immediate dialysis, for tunnelled access in patients who are deemed likely to recover from acute renal failure, and for patients with end-stage renal failure who are either waiting for alternative access to mature or who are unable to have alternative access.

Catheter access is often popular with patients, because attachment to the dialysis machine doesn't require needles. However, the serious risks of catheter access noted above mean that such access should be contemplated only as a long-term solution in the most desperate access situation.

5.2.11 Typical Electronic Circuits in the Dialysis Machine could be:

Sensor Control Board: Contains Analog to Digital Converters, precision references, Clocks and VCOs as well as instrumentation or operation amplifiers. Although these circuits need to respond quickly, the devices included here are often geared more towards precision than what is considered high speed today. Part of that is also driven by the need to verify a measurement or alarm signal and coordinating the response across the entire system, versus just reacting to random stimuli. The A/Ds used here would provide high reliability, good noise immunity

(note that there are motors and pumps in the system), and good precision.

Arterial And Venous Control Card: These portions of a system may include functions like; Arterial and Venous Pressure Sensors, Blood Pumps, Line Clamps, Level Sensors, blood detection Sensors, and various other monitoring and control features. Since TI's C2xxx DSPs are targeted at Motor drive and Industrial Sensor applications, they are ideally suited as the microcontroller for these blocks. Providing not only the drive and diagnostic capabilities, but also allowing the implementation of RPM, and motor coil current sensing, as well as reading the pressure transducers. There can also support the redundancy required in the system at a minimal cost impact.

Motor/Pump Drivers: There are a number of motors, pumps, valves and heaters in a Dialysis machine. Each may need a specific drive circuit, where as some may be able to be driven directly for a C2xxx controller. Selecting the right D/A converter and drive amplifier is important to the control of the motor/pump, as well as to the life expectancy of the motor/pump. Driving any of the values or motors to hard, with signals that are to noisy can cause them to run hot and degrade quickly, as well as impact the overall comfort of the patient connected to the machine.

From TI's C2xxx family of high performance 32-Bit Controllers, through its Precisions Analog offering of Amplifiers and Data Converters, to a broad range of power management solutions, the right components with the right support are available from TI.

6. treatement summary

7. Types

There are three types of hemodialysis: conventional hemodialysis, daily hemodialysis, and nocturnal hemodialysis. Below is the adaption and summary from a brochure of The Ottawa Hospital.

7.1 Conventional hemodialysis

Chronic hemodialysis is usually done three times per week, for about 3–4 hours for each treatment, during which the patient's blood is drawn out through a tube at a rate of 200-400 mL/min. The tube is connected to a 15, 16, or 17 gauge needle inserted in the dialysis fistula or graft, or connected to one port of a dialysis catheter. The blood is then pumped through the dialyzer, and then the processed blood is pumped back into the patient's bloodstream through another tube (connected to a second needle or port). During the procedure, the patient's blood pressure is closely monitored, and if it becomes low, or the patient develops any other signs of low blood volume such as nausea, the dialysis attendant can administer extra fluid through the machine. During the treatment, the patient's entire blood volume (about 5000 cc) circulates through the machine every 15 minutes. During this process, the dialysis patient is exposed to a weeks worth of water for the average person.

7.2 Daily hemodialysis

Daily hemodialysis is typically used by those patients who do their own dialysis at home. It is less stressful (more gentle) but does require more frequent access. This is simple with catheters, but more problematic with fistulas or grafts. The "buttonhole technique" can be used for fistulas requiring frequent access. Daily hemodialysis is usually done for 2 hours six days a week.

7.3 Nocturnal hemodialysis

The procedure of nocturnal hemodialysis is similar to conventional hemodialysis except it is performed three to six nights a week and between six and ten hours per session while the patient sleeps.

Membrane and flux

Dialyzer membranes come with different pore sizes. Those with smaller pore size are called "low-flux" and those with larger pore sizes are called "high-flux." Some larger molecules, such as beta-2-microglobulin, are not removed at all with low-flux dialyzers; lately, the trend has been to use high-flux dialyzers. However, such dialyzers require newer dialysis machines and high-quality dialysis solution to control the rate of fluid removal properly and to prevent backflow of dialysis solution impurities into the patient through the membrane.

Dialyzer membranes used to be made primarily of cellulose (derived from cotton linter). The surface of such membranes was not very biocompatible, because exposed hydroxyl groups would activate complement in the blood passing by the membrane. Therefore, the basic, "unsubstituted" cellulose membrane was modified. One change was to cover these hydroxyl groups with acetate groups (cellulose acetate); another was to mix in some compounds that would inhibit complement activation at the membrane surface (modified cellulose). The original "unsubstituted cellulose" membranes are no longer in wide use, whereas cellulose

acetate and modified cellulose dialyzers are still used. Cellulosic membranes can be made in either low-flux or high-flux configuration, depending on their pore size.

Another group of membranes is made from synthetic materials, using polymers such as polyarylethersulfone, polyamide, polyvinylpyrrolidone, polycarbonate, and polyacrylonitrile. These synthetic membranes activate complement to a lesser degree than unsubstituted cellulose membranes. Synthetic membranes can be made in either low- or high-flux configuration, but most are high-flux.

Nanotechnology is being used in some of the most recent high-flux membranes to create a uniform pore size. The goal of high-flux membranes is to pass relatively large molecules such as beta-2-microglobulin (MW 11,600 daltons), but not to pass albumin (MW ~66,400 daltons). Every membrane has pores in a range of sizes. As pore size increases, some high-flux dialyzers begin to let albumin pass out of the blood into the dialysate. This is thought to be undesirable, although one school of thought holds that removing some albumin may be beneficial in terms of removing protein-bound uremic toxins.

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.

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 beta-2-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.

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.

Alarms and Troubleshooting

This chapter covers atypical situations such as alarm and warning events that can occur during treatment. At the end of this chapter are also procedures for testing the Diasafe Filter and replacing the power failure alarm battery.

Operational Status

The hemodialysis machine is equipped with a system of electronic components and diagnostic software that monitor its operation and performance. When problems or potential problems are detected, the operator is alerted through informational messages displayed on the screen and in some cases, audible alarms. Audible alarms are suppressed however, when the dialysate supply lines are on the shunt, providing no blood is sensed.

The informational messages are displayed in two places in each treatment screen: the Status Box and the Dialogue Box. The Status Box is present in every screen. The Dialogue Box appears in place of the Time and Blood Pressure boxes in the Dialogue Box in situations requiring input from the operator.

The Status Box is a rectangular box found in the upper left corner of every screen. The message in it describes the current mode of the machine or a problem during treatment. There are three operational conditions or statuses: Normal, Warning, and Alarm. The background color of the Status Box changes color to accentuate the operational status. Depending on the options chosen, machines that are equipped with a status beacon may illuminate the light to alert the user of the machine status.

The Dialogue Box, found in the upper right corner of the display screens, can provide information on the patient, prompt an action, or serve as a reminder. The Dialogue Box can appear alone or supplement the message displayed in the Status Box during a Warning condition. In some cases, Dialogue Boxes, if ignored for a prolonged period, can trigger a Warning message in the Status Box. Although a Dialogue Box can appear during a Warning or Alarm event, the messages displayed in each may represent two separate, unrelated issues.

Normal Status

The Status Box displays a green background under normal operation when no problems have been detected. During dialysis operation, the Status box will display a message describing the current mode of the machine—DIALYSIS. When a Dialogue Box message is not

displayed, the Dialogue Box displays the current time, patient blood pressure and pulse and the time taken.

Warning Status

The Status Box background changes to yellow when a Warning condition exists. A Warning condition, although potentially serious, does not pose an immediate threat to the patient. Warning events do not stop the blood pump. The message displayed in the Status Box is intended to alert the operator of a functional anomaly, a procedural error, or an existing condition requiring remedial action. A warning may be accompanied by an audible alarm.

Alarm Status

Alarm situations require the immediate attention of the operator. Under these circumstances, the background of the Status Box turns bright red. An audible alarm also accompanies these alarm events.

There are three types of:

1. Blood Alarms

Blood alarm events have the highest priority. When a blood alarm occurs: The blood pump stops. The venous clamp on the level detector occludes. The UF pump stops. RTD stops There are several features on the 2008T hemodialysis machine control panel that you should be familiar with in the event of a blood alarm. Figure 58 - Control Panel Features for Blood Alarms identifies the location of each of them. The accompanying table describes the function of each feature.

2. Dialysate Alarms

During a dialysate alarm (temperature or conductivity), the blood system continues to operate, but the dialysate fluid is internally bypassed around the dialyzer. This can be

verified by visually inspecting the flow meter in the dialysate supply line. During bypass, the float will remain stationary at the bottom of the sight glass.

A flow alarm will not cause the machine to go into bypass. Dialysate alarms are self-resetting when the alarm condition is corrected. Temperature and conductivity alarms do not occur during the pure UF mode of Sequential dialysis when there is no dialysate flow.

3. Other Alarms Other alarms may be associated with other components, such as the Heparin or UF pumps, BPM, BVM, BTM, etc.

Troubleshooting

All status messages (operational alarms, warnings, dialogues, and advisories) are displayed on the control panel screen. These messages are generated due to conditions and events that occur in the machine during operation. These messages will reset when the condition causing the message is corrected. In some cases, the operator must reset them.

The table following this section is indexed by Status box message. The table consists of four columns: Status Box Message Message Purpose Message Type Action Required

Advantages and disadvantages

Advantages

1. Low mortality rate2. Better control of blood pressure and abdominal cramps3. Less diet restriction4. Better solute clearance effect for the daily hemodialysis: better tolerance and fewer

complications with more frequent dialysis.

Disadvantages

1. Restricts independence, as people undergoing this procedure cannot travel around because of supplies’ availability

2. Requires more supplies such as high water quality and electricity3. Requires reliable technology like dialysis machines4. The procedure is complicated and requires that care givers have more knowledge

5. Requires time to set up and clean dialysis machines, and expense with machines and associated staff.

6. Side effects and complications: Hemodialysis often involves fluid removal (through ultrafiltration), because most patients with renal failure pass little or no urine. Side effects caused by removing too much fluid and/or removing fluid too rapidly include low blood pressure, fatigue, chest pains, leg-cramps, nausea and headaches. These symptoms can occur during the treatment and can persist post treatment; they are sometimes collectively referred to as the dialysis hangover or dialysis washout. The severity of these symptoms is usually proportionate to the amount and speed of fluid removal. However, the impact of a given amount or rate of fluid removal can vary greatly from person to person and day to day. These side effects can be avoided and/or their severity lessened by limiting fluid intake between treatments or increasing the dose of dialysis e.g. dialyzing more often or longer per treatment than the standard three times a week, 3–4 hours per treatment schedule.

Since hemodialysis requires access to the circulatory system, patients undergoing hemodialysis may expose their circulatory system to microbes, which can lead to sepsis, an infection affecting the heart valves (endocarditis) or an infection affecting the bones (osteomyelitis). The risk of infection varies depending on the type of access used (see below). Bleeding may also occur, again the risk varies depending on the type of access used. Infections can be minimized by strictly adhering to infection control best practices.

Heparin is the most commonly used anticoagulant in hemodialysis, as it is generally well tolerated and can be quickly reversed with protamine sulfate. Heparin allergy can infrequently be a problem and can high risk of bleeding, dialysis can be done without anticoagulation.

First Use Syndrome is a rare but severe anaphylactic reaction to the artificial kidney. Its symptoms include sneezing, wheezing, shortness of breath, back pain, chest pain, or sudden death. It can be caused by residual sterilant in the artificial kidney or the material of the membrane itself. In recent years, the incidence of First Use Syndrome has decreased, due to an increased use ofgamma irradiation, steam sterilization, or electron-beam radiation instead of chemical sterilants, and the development of new semipermeable membranes of higher biocompatibility. New methods of processing previously acceptable components of dialysis must always be considered. For example, in 2008, a series of first-use type or reactions, including deaths occurred due to heparin contaminated during the manufacturing process with oversulfated chondroitin sulfate.

Longterm complications of hemodialysis include amyloidosis, neuropathy and various forms of heart disease. Increasing the frequency and length of treatments have been shown to improve fluid overload and enlargement of the heart that is commonly seen in such patients.