Dialysis is a procedure used to remove endogenous toxic metabolites as in uremia/renal failure, inborn errors of metabolism (with accumulation of organic acids) across a semipermeable membrane. It is also useful in removing exogenous poisons like ethanol, aspirin, barbiturates, and boric acid from the blood in cases of poisoning.
Hemodialysis is a method of dialysis where vascular access is used along with an artificial semipermeable membrane pack in a dialyser and controlled by a dialysis machine, so that transfer of solutes and fluid from blood to the dialysate fluid takes place in a controlled manner, by extracorporeal perfusion. (Fig. of a dialyser)
Components for hemodialysis
For hemodialysis, 3 components are required:
Vascular access: arteriovenous connection
Dialyser: a disposable equipment, which holds a bundle of semipermeable membranes either polymerized or made of cellulose acetate cuprophane. The size of the dialyser varies according to the surface area of the patient. For children, pediatric size dialysers should be used. One end of the dialyser is connected to the arterial end and the other end to venous side of vascular access and the access for dialysate fluid. The semipermeable membrane separates the blood compartment and dialysate compartment and allows the transfer of solute from blood to the dialysate, which is drained out after dialysis is completed. The programmed removal of nitrogenous waste products, excess potassium, sodium and water is controlled by computerized dialysis machine.
Dialysis machine: It controls the flow of blood, dialysate fluid (which is prepared by adding water to the purified concentrate) and the amount of water, sodium and other noxious substances which need to be removed during 3-4 hours of dialysis. Advances in bioengineering and technical aspects of dialysis machines have made hemodialysis a safe and effective procedure.
Indications of hemodialysis are acute renal failure or poisoning, chronic renal failure/ end stage renal disease and rarely inborn errors of metabolism, cardiac failure. Chronic maintenance hemodialysis (CMHD) is given 3 times a week. Each session of dialysis is for 3-4 hours.
Types of arteriovenous connections
A-V Shunt: Surgically, a silastic catheter is placed which connects radial artery to cephalic vein or femoral artery to femoral vein. The arterial and venous ends of the shunt are connected to arterial and venous ends of the dialyser when dialysis is to be commenced. This type of vascular access is rarely used because of high rate of blocking of the shunt.
A-V fistula: The radial artery is surgically anastomosed to cephalic vein in forearm. Ulnar-Basilic or saphenous vein loop are other fistulae used for hemodialysis. Two needles are introduced once the fistula matures and is functionally ready to connect the dialyser to fistula. In this method of vascular access, no foreign material is used.
A-V graft: Teflon/PTFE graft is used to connect arterial to venous or veno-venous anastomosis. The major problem in young children are the small sized vessels, which are responsible for failure of vascular access. This graft is expensive and not available in India.
Currently dual lumen venous catheters, which can be introduced in subclavian, jugular or femoral veins are commonly used as vascular access for hemodialysis.
Peritoneal dialysis (PD) is the type of dialysis when peritoneal membrane is used as a semipermeable membrane for transfer of solutes and fluid from blood to the dialysate fluid which is infused by special peritoneal dialysis catheters and tubes and periodically removed after the dialysis procedure is completed.
Peritoneal dialysis is used as a renal replacement therapy acutely in acute renal failure, poisonings (though hemodialysis is more efficient). Intermittently or long term PD is used for chronic renal failure /ESRD. The indications of PD are almost same as HD.
PD procedure involves introduction of PD catheter in the peritoneal cavity using a trocar or placement of tenchkoff catheter surgically in the peritoneum (permanent access) when chronic PD is indicated. The catheter is attached to tubings and special bags containing dialysate fluid which infuse special PD fluid into peritoneal cavity (inflow) for ½ hr for acute cases and for a longer time in CAPD. The transfer of solutes takes place and after opening the clamps, the dialysate fluid is discarded in a bag (out flow). Such 20-24 cycles of PD can be given over 24-48 hours for acute PD.
Continuous ambulatory peritoneal dialysis (CAPD)
For chronic PD, the procedure is almost the same but intermittent introduction of catheter being difficult, permanent access using tenchkoff catheter is made. The dialysate fluid is infused and allowed to remain in peritoneal cavity for 4-6 hours after which it is drained in the empty bags. Three to four exchanges per day of PD are done by the relatives of the child or the patient himself/herself after a training period of 2-3 weeks. Thus, the patient is ambulatory and can attend school and carry out normal activities. The continuous ambulatory peritoneal dialysis is physiological and can be managed at home. The growth, control of anemia, hypertension etc is better with CAPD than chronic HD and convenient for the family.
Monitoring on PD
The patients on chronic dialysis require continuous treatment to remove accumulated nitrogenous toxic metabolites every 48-72 hours because of failure of the kidneys to perform these functions. Every 30-40 days, renal parameters in blood need to be monitored. B.P, Hb% are done every month. Fluid intake and diet needs to be checked by the dietician strictly. Height should be monitored 3 monthly. During the dialysis procedure - Pulse, temperature, BP, problems such as hypotension, volume overload, infection, fluid and electrolyte imbalance, seizures and CNS problems are monitored by expert nursing staff specially trained for dialysis and supervised by nephrologists.
Peritoneal Dialysis or HemodialysisDecision regarding whether PD or HD should be done depends on age of the child, whether the indication is for acute or chronic dialysis, socioeconomic state and expertise available in the hospital.
In small infants and children, the vascular access is difficult, hence PD is preferred. Because the procedure is simple, quick, the equipment and fluid are easily available; peritoneal dialysis is preferred for acute renal failure.
For chronic dialysis in India, hemodialysis is preferred because the cost of bags containing PD fluid is very high. Although worldwide, CAPD is gaining popularity for ESRD in children because of home based dialysis, freedom to pursue studies, play, activity, less number of needle pricks, no visits to hospitals etc.
PrognosisPrognosis of a patient on dialysis is good. In acute renal failure, dialysis is life saving and complete recovery is possible. For chronic renal failure/ESRD dialysis can maintain fairly good quality of life, but restriction of activity and continuous or intermittent medical check ups, hospitalization interrupt the daily life.
When to do renal transplant?Renal transplant is preferred treatment for patients with ESRD and a healthy kidney from a compatible donor is the final solution to the problem of ESRD who is on dialysis. In children, renal transplantation without dialysis or after a short period of dialysis to stabilize the child while preparing for transplant is the best treatment (pre -empirical renal transplant) to achieve normal growth.