Dialysis

Introduction

Human kidneys perform the vital function of eliminating metabolic wastes from the body. Any failure of the kidneys to naturally perform their functions would become a matter of life or death for the patient. This is where ‘dialysis’ comes into the picture as a lifesaver. Dialysis is derived from the Greek words ‘dia’ meaning through and ‘lysis’ meaning splitting or separating. It is a medical procedure to treat patients whose kidneys have stopped functioning. This procedure helps remove waste products like water, solutes and other toxins from the patient’s blood. It helps treat patients ailing from acute renal failure or chronic stage 5 kidney ailments.

Principle of dialysis

The principles of diffusion and ultrafiltration are pivotal to dialysis. Diffusion is the property of solutes. It alters the position of the solutes from an area of high concentration to one of low concentration. Solutes are diffused and the fluid is ultra-filtered through a semipermeable membrane. A semipermeable membrane is a thin layer of porous material. A special dialysis fluid flows on one side of the semipermeable membrane while the blood flows through the other side. Tiny solutes and fluids permeate through the membrane, but the membrane blocks out the passage of larger substances like red blood cells and large proteins, thereby replicating the function of kidneys which separates the bigger substances from the smaller ones in the glomerulus.

Types of dialysis

Broadly, there are five types of dialysis. They are:

• Haemodialysis
• Peritoneal dialysis
• Haemofiltration
• Haemodiafiltration
• Intestinal dialysis

Haemodialysis

In haemodialysis, the patient’s blood is exposed to a partially permeable membrane after being pumped through the blood compartment of a dialyser that is composed of thousands of tiny hollow synthetic fibres. The fibre wall performs the function of a semipermeable membrane. The dialysis solution flows around the outside of the hollow synthetic fibres while blood flows through the fibre walls. The resultant water and wastes move between these two solutions. Application of negative pressure to the dialysate compartment of the dialyser increases the hydrostatic pressure across the dialyser membrane resulting in ultrafiltration. Water and dissolved solutes separate from the blood to the dialysate and remove several litres of toxins and waste fluids during clinical treatment of 4 hours. The cleansed blood is channelised through the circuit back into the human body.

Types of haemodialysis

Listed below are the types of haemodialysis:

• Conventional haemodialysis
• Daily haemodialysis
• Nocturnal haemodialysis

Conventional haemodialysis

The frequency of conventional haemodialysis is thrice weekly, and each treatment lasts for about three to four hours and sometimes even five hours for larger patients. The patient’s blood is drawn out through a tube during the procedure. The tube is connected to a gauge needle inserted in the dialysis fistula or graft, thus, connecting it to one port of a dialysis catheter. The blood from the patient is then pumped through the dialyser. The processed blood is later pumped back into the patient’s bloodstream through another tube connected to a second needle or port. The patient’s blood pressure is closely monitored during the whole procedure. If it drops, or if the patient develops any symptoms of low blood volume such as nausea, the dialysis attendant administers extra fluid to control the same. The dialysis involves the circulation of the patient’s complete blood volume of about 5000 ccs through the dialysis machine every 15 minutes. The patient is exposed to an average person’s week’s worth of water.

Daily haemodialysis

Patients who prefer to do their dialysis from the comfort of their homes opt for daily haemodialysis. It requires more frequent access but is a gentler procedure. Daily haemodialysis tends to be more straightforward with catheters but gets more complicated with fistulas or grafts. The “buttonhole technique” is useful in dialysis involving fistulas requiring frequent access. The frequency of daily haemodialysis is two hours per day, six days a week.

Nocturnal haemodialysis

Nocturnal haemodialysis is similar to conventional haemodialysis, except that it is performed three to six nights a week. Each session takes between six to ten hours to complete. As the term suggests, it is conducted while the patient sleeps.

Peritoneal dialysis

In peritoneal dialysis, dialysate – a sterile electrolyte-containing solution – is run through a tube into the peritoneal cavity, the abdominal body cavity around the intestine. Here, the peritoneal membrane acts as a partially permeable membrane. The procedure is repeated four to five times daily. Automated systems execute more frequent exchange cycles overnight.

Haemofiltration dialysis

Haemofiltration, though similar to haemodialysis, is different in its principle. As in haemodialysis, the blood is pumped through a dialyser or “haemofilter,” but without the dialysate. An applied pressure gradient moves the water across the very permeable membrane rapidly. This process drags many dissolved substances, including ones with large molecular weights, uncleared by haemodialysis. Loss of salts and water from blood during the dialysis is replaced with a substitution fluid infused into the extracorporeal circuit during the process.

Haemodiafiltration dialysis

Haemodiafiltration combines haemodialysis and haemofiltration to purify the blood when the kidney malfunctions. It is also used to treat acute kidney injury.

Intestinal dialysis

Intestinal dialysis revolves around the principle of soluble fibres such as acacia fibre acting as a dietary supplement to increase the rate of nitrogen elimination through faecal waste. The digestion of these fibres results in increased growth of bacteria in the colon, producing a vast amount of nitrogen. Alternatively, 1 to 1.5 litres of non-absorbable solutions of polyethene glycol or mannitol are ingested every fourth hour.

Indicators

The decision-making process for commencing dialysis or haemofiltration in patients with kidney failure depends on several factors and is classified as acute or chronic indications.

Acute indications

• The vowel mnemonic of “AEIOU” is the summation of indications for dialysis in a patient with acute kidney injury
• Acidemia from metabolic acidosis in the circumstances where correction with sodium bicarbonate is impractical or may result in fluid overload
• Electrolyte abnormality, such as severe hyperkalaemia, especially when combined with acute kidney injury
• Intoxication is acute poisoning with a dialysable substance
• Overload of fluid not responding to treatment with diuretics
• Uremia complications like pericarditis, encephalopathy or gastrointestinal bleeding

Chronic indications

Chronic dialysis is indicated in patients with symptomatic kidney failure and low glomerular filtration rate (GFR) < 15 mL/min.

Conclusion

Patients ailing from a sudden rapid loss of kidney function, known as acute kidney injury (previously called acute renal failure), may need dialysis. Patients ailing from a gradual decline in kidney function or chronic stage 5 kidney disease also need dialysis. Stage 5 chronic renal failure is indicated when the glomerular filtration rate (GFR) is 10–15% of normal, creatinine clearance is less than 10 mL per minute and there is a presence of uremia. Dialysis is performed in

• acute kidney injury cases
• those awaiting a kidney transplant, as a temporary measure
• those patients for whom a transplant is impossible or non-indicative, as a permanent measure