Dialysis
In medicine dialysis (from Greek "dialusis", meaning dissolution, "dia", meaning through, and "lysis", meaning loosening) is primarily used to provide an artificial replacement for lost kidney function in people with renal failure. Dialysis may be used for those with an acute disturbance in kidney functison ( acute kidney injury, previously acute renal failure) or for those with progressive but chronically worsening kidney function–a state known as chronic kidney disease stage 5 (previously chronic renal failure or end-stage kidney disease). The latter form may develop over months or years, but in contrast to acute kidney injury is not usually reversible, and dialysis is regarded as a "holding measure" until a renal transplant can be performed, or sometimes as the only supportive measure in those for whom a transplant would be inappropriate.
The kidneys have important roles in maintaining health. When healthy, the kidneys maintain the body's internal equilibrium of water and minerals (sodium, potassium, chloride, calcium, phosphorus, magnesium, and sulfate). Those acidic metabolism end products that the body cannot get rid of via respiration are also excreted through the kidneys. The kidneys also function as a part of the endocrine system producing erythropoietin and calcitriol. Erythropoietin is involved in the production of red blood cells and calcitriol plays a role in bone formation. Dialysis is an imperfect treatment to replace kidney function because it does not correct the endocrine functions of the kidney. Dialysis treatments replace some of these functions through diffusion (waste removal) and ultrafiltration (fluid removal).
When does patient need dialysis
Patients usually require dialysis when the waste products in their body become so high that they start to become sick from them. The level of the waste products usually builds up slowly. Doctors measure several blood chemical levels to help decide when dialysis is necessary. The two major blood chemical levels that are measured are the "creatinine level" and the “blood urea nitrogen” (BUN) level. As these two levels rise, they are indicators of the decreasing ability of the kidneys to cleanse the body of waste products.
Doctors use a urine test, the "creatinine clearance," to measure the level of kidney function. The patient saves urine in a special container for one full day. The waste products in the urine and in the blood are estimated by measuring the creatinine. By comparing the blood and urine level of this substance, the doctor has an accurate idea of how well the kidneys are working. This result is called the creatinine clearance. Usually, when the creatinine clearance falls to 10-12 cc/minute, the patient needs dialysis.
The doctor uses other indicators of the patient's status to decide about the need for dialysis. If the patient is experiencing a major inability to rid the body of excess water, or is complaining of problems with the heart, lungs, or stomach, or difficulties with taste or sensation in their legs, dialysis may be indicated even though the creatinine clearance has not fallen to the 10-12 cc/minute level.
Indications for starting dialysis:
- Oliguria (urine output <200 mL/12 h)
- Anuria/extreme oliguria (urine output <50 mL/12 h)
- Hyperkalemia ([K] >6.5 mEq/L)
- Severe acidemia (pH <7.1)
- Azotemia ([urea] >30 mg/dL)
- Clinically significant organ (especially pulmonary) edema
- Uremic encephalopathy
- Uremic pericarditis
- Uremic neuropathy/myopathy
- Severe dysnatremia ([Na] <115 or >160 mEq/L)
- Hyperthermia
- Drug overdose with dialyzable toxin
Principle:
Dialysis works on the principles of the diffusion of solutes and ultrafiltration of fluid across a semi-permeable membrane. Diffusion describes a property of substances in water. Substances in water tend to move from an area of high concentration to an area of low concentration. Blood flows by one side of a semi-permeable membrane, and a dialysate, or special dialysis fluid, flows by the opposite side. A semipermeable membrane is a thin layer of material that contains various sized holes, or pores. Smaller solutes and fluid pass through the membrane, but the membrane blocks the passage of larger substances (for example, red blood cells, large proteins).
The two main types of dialysis, hemodialysis and peritoneal dialysis, remove wastes and excess water from the blood in different ways. Hemodialysis removes wastes and water by circulating blood outside the body through an external filter, called a dialyzer that contains a semipermeable membrane. The blood flows in one direction and the dialysate flows in the opposite. The counter-current flow of the blood and dialysate maximizes the concentration gradient of solutes between the blood and dialysate, which helps to remove more urea and creatinine from the blood. The concentrations of solutes (for example potassium, phosphorus, and urea) are undesirably high in the blood, but low or absent in the dialysis solution and constant replacement of the dialysate ensures that the concentration of undesired solutes is kept low on this side of the membrane. The dialysis solution has levels of minerals like potassium and calcium that are similar to their natural concentration in healthy blood. For another solute, bicarbonate, dialysis solution level is set at a slightly higher level than in normal blood, to encourage diffusion of bicarbonate into the blood, to act as a pH buffer to neutralize the metabolic acidosis that is often present in these patients. The levels of the components of dialysate are typically prescribed by a nephrologist according to the needs of the individual patient.
In peritoneal dialysis, wastes and water are removed from the blood inside the body using the peritoneal membrane of the peritoneum as a natural semipermeable membrane. Wastes and excess water move from the blood, across the peritoneal membrane, and into a special dialysis solution, called dialysate, in the abdominal cavity which has a composition similar to the fluid portion of blood.
Types:
There are three primary and two secondary types of dialysis: hemodialysis (primary), peritoneal dialysis (primary), hemofiltration (primary), hemodiafiltration (secondary), and intestinal dialysis (secondary).
Hemodialysis:
In hemodialysis, the patient's blood is pumped through the blood compartment of a dialyzer, exposing it to a partially permeable membrane. The dialyzer is composed of thousands of tiny synthetic hollow fibers. The fiber wall acts as the semipermeable membrane. Blood flows through the fibers, dialysis solution flows around the outside of the fibers, and water and wastes move between these two solutions. The cleansed blood is then returned via the circuit back to the body. Ultrafiltration occurs by increasing the hydrostatic pressure across the dialyzer membrane. This usually is done by applying a negative pressure to the dialysate compartment of the dialyzer. This pressure gradient causes water and dissolved solutes to move from blood to dialysate, and allows the removal of several litres of excess fluid during a typical 3 to 5 hour treatment. In the US, hemodialysis treatments are typically given in a dialysis center three times per week (due in the US to Medicare reimbursement rules); however, as of 2007 over 2,500 people in the US are dialyzing at home more frequently for various treatment lengths. Studies have demonstrated the clinical benefits of dialyzing 5 to 7 times a week, for 6 to 8 hours. This type of hemodialysis is usually called "nocturnal daily hemodialysis", which a study has shown a significant improvement in both small and large molecular weight clearance and decrease the requirement of taking phosphate binders. These frequent long treatments are often done at home while sleeping, but home dialysis is a flexible modality and schedules can be changed day to day, week to week. In general, studies have shown that both increased treatment length and frequency are clinically beneficial.
Peritoneal dialysis:
In peritoneal dialysis, a sterile solution containing glucose is run through a tube into the peritoneal cavity, the abdominal body cavity around the intestine, where the peritoneal membrane acts as a semipermeable membrane.The peritoneal membrane or peritoneum is a layer of tissue containing blood vessels that lines and surrounds the peritoneal, or abdominal, cavity and the internal abdominal organs (stomach, spleen, liver, and intestines). The dialysate is left there for a period of time to absorb waste products, and then it is drained out through the tube and discarded. This cycle or "exchange" is normally repeated 4-5 times during the day, (sometimes more often overnight with an automated system). Each time the dialysate fills and empties from the abdomen is called one exchange. A dwell time means that the time of dialysate stay in patient's abdominal cavity - wastes, chemicals and extra fluid move from patient's blood to the dialysate across the peritoneum. A drain process is the process after the dwell time, the dialysate full with waste products and extra fluid is drained out of patient's blood. Ultrafiltration occurs via osmosis; the dialysis solution used contains a high concentration of glucose, and the resulting osmotic pressure causes fluid to move from the blood into the dialysate. As a result, more fluid is drained than was instilled. Peritoneal dialysis is less efficient than hemodialysis, but because it is carried out for a longer period of time the net effect in terms of removal of waste products and of salt and water are similar to hemodialysis. Peritoneal dialysis is carried out at home by the patient. Although support is helpful, it is not essential. It does free patients from the routine of having to go to a dialysis clinic on a fixed schedule multiple times per week, and it can be done while travelling with a minimum of specialized equipment.
Hemofiltration
Hemofiltration is a similar treatment to hemodialysis, but it makes use of a different principle. The blood is pumped through a dialyzer or "hemofilter" as in dialysis, but no dialysate is used. A pressure gradient is applied; as a result, water moves across the very permeable membrane rapidly, "dragging" along with it many dissolved substances, importantly ones with large molecular weights, which are cleared less well by hemodialysis. Salts and water lost from the blood during this process are replaced with a "substitution fluid" that is infused into the extracorporeal circuit during the treatment. Hemodiafiltration is a term used to describe several methods of combining hemodialysis and hemofiltration in one process.
Hemodiafiltration
Hemodialfiltration is a combination of hemodialysis and hemofiltration. In theory, this technique offers the advantages of both hemodialysis and hemofiltration.
Intestinal dialysis
In intestinal dialysis, the diet is supplemented with soluble fibres such as acacia fibre, which is digested by bacteria in the colon. This bacterial growth increases the amount of nitrogen that is eliminated in fecal waste. An alternative approach utilizes the ingestion of 1 to 1.5 liters of non-absorbable solutions of polyethylene glycol or mannitol every fourth hour.
Starting indications
The decision to initiate dialysis or hemofiltration in patients with renal failure depends on several factors. These can be divided into acute or chronic indications.
- Indications for dialysis in the patient with acute kidney are :
- Metabolic acidosis in situations where correction with sodium bicarbonate is impractical or may result in fluid overload.
- Electrolyte abnormality, such as severe huperkalemia, especially when combined with AKI.
- Fluid overloaded not expected to respond to treatment with diuretics.
- Complications of uremia, such as pericarditis, encephalopathy, or gastrointestinal bleeding.
- Intoxication, that is, acute poisoning with a dialyzable substance. These substances can be represented by the mnemonic SLIME: salicylic acid, Lithium, isopropanol, Magnesium-containing laxatives, and ethylene glycol.
- Chronic indications for dialysis:
- Symptomatic renal failure
- Low glomerular filtration rate (GFR) ( RRT often recommended to commence at a GFR of less than 10-15 mls/min/1.73m2). In diabetics dialysis is started earlier.
- Difficulty in medically controlling fluid overload, serum potassium, and/or serum phosphorus when the GFR is very low
Risks and Side Effects During Kidney Dialysis
It's important to remember that without dialysis, many patients' only hope is a transplant. The risks associated with refusing dialysis are MUCH worse than those due to dialysis. Rather than panic at these potential problems, speak to your own doctor for a fuller explanation.
Bleeding from the Access Point
As dialysis is an invasive technique, the area surrounding the access point can be damaged and bleeding can occur. You should see your doctor if this occurs.
Hypotension
Dialysis patients are at risk of a sudden drop in blood pressure (hypotension), due to the stress the cardiovascular system is under from regular hemodialysis. However this can be controlled by medication.
Infections
Dialysis patients are generally more susceptible to infection. The access point should be kept clean, and any sign of infection (redness, itching, or other problems) watched for. Peritonitis with its associated flu-like symptoms is also a possibility. Hence the importance of cleanliness and good general hygiene.
Cramps, Nausea and Headaches
These flu-like symptoms are sometimes experienced by hemodialysis patients. The water quality in the dialyzer, the composition of the dialyser itself, the dialysate composition, and the rate of filteration can all cause problems, which can be reduced by adjusting the dialysis perscription. However, do remember that these are also symptoms of peritonitis.
Electrolyte Imbalance
This will almost certainly be detected via the normal blood tests conducted on dialysis patients. There are a variety of vital electrolytes (ionic species) in the blood that control a number of bodily process and this is too general an area for discussion here.
Anemia
The red blood cell volume in dialysis patients (especially hemodialysis patients) is often lower then normal. This is due to reduced levels of the hormone erythropoietin, which is produced by the kidneys and regulates red blood cell production. Medication to treat the anemia is commonly used by dialysis patients.
Infectious diseases
During hemodialysis, there is a slight risk of getting hepatitis B and hepatitis C. But you can be vaccinated against hepatitis B, something which is generally recommended to most patients on hemodialysis. Due to the strict standards enforced to reduce infections in modern hemodialysis centers, however, the chance of being infected is very small.
Comments
Post a Comment