Renal (kidney) dialysis is a treatment designed to make a machine take over functions of the kidneys.
Dialysis is a treatment designed to make a machine take over functions normally performed by normal kidneys. That is, to remove uremic toxins, and normalize body fluid and electrolytes. Even so, dialysis is not nearly as efficient as normal native kidneys.
Dialysis is like “switching” normal kidney function on during treatment and off between treatments. Of the two dialytic treatments (hemodialysis, peritoneal dialysis), hemodialysis is more efficient per unit of time (e.g. per hour) than is peritoneal dialysis. On the other hand, peritoneal dialysis is safer and easier in infants and small children.
Toxin removal in both dialytic treatments depends on the phenomenon of osmosis. That is, if two compartments are separated by a semi-permeable membrane and one compartment (in this case, the body) contains uremic toxins and excess electrolytes (e.g., sodium, potassium), and the compartment on the other side of the membrane (dialysate) is free of these substances, toxins and electrolytes will move across the membrane until they are in equal concentrations on both sides. In peritoneal dialysis (PD), excess body fluid (edema) is removed by making dialysate hypertonic (by the addition of dextrose).
Fluid moves across the membranes until the osmotic concentration is equal on both sides of the membrane. If the fluid (dialysate) is continually being replaced, the process can be continued until fluid balance is achieved. With hemodialysis (HD), excess fluid is removed by creating pressure gradients between the blood and dialysate compartments.
Peritoneal Dialysis (PD)
Peritoneal dialysis is usually best for infants and small children, but it can also be used in teens and adults. In children it can be done at home while the child sleeps. There are now several automated machines that infuse a set volume of warmed dialysate that remains for a set period of time and is then drained.
In order to perform PD, a catheter is surgically placed in the peritoneal cavity where the semi-permeable membrane is the peritoneal membrane that lines the peritoneal cavity and the outer surface of the intestines. The cycle of infusion, dwell, and drainage, usually occurs 10-12 times a night (e.g., hourly). Since there is no danger of blood loss (as there is with hemodialysis), there is no need for continual monitoring by the parents. If the fluid stops flowing in and out of the peritoneal cavity, an alarm sounds, and the parents can call the dialysis staff for advice.
Although it is less efficient (per unit of time) than hemodialysis, PD is gentler on the circulatory system because it removes toxins and excess body fluid, and balances electrolytes more slowly. The major drawback is the risk of peritonitis, which is a bacterial infection of the peritoneal cavity. Parents are trained to recognize the signs of peritonitis, and to collect a sample of the dialysate fluid (which is usually cloudy), and to take it to the nearest laboratory for a gram stain which identifies bacteria, a culture, that documents the type of bacteria, and determines antimicrobial sensitivities (for selection of the appropriate antibiotic).
Antibiotics are added to the dialysate, allowing treatment at home, with daily phone contact with the dialysis staff, as long as the child is stable with no signs of sepsis (systemic infection). Children whose condition is unstable, and infants, need to be hospitalized.
Hemodialysis is more suitable for older children, adolescents, and adults, but can be used in small children and even infants if PD is no longer effective. For example, PD sometimes loses effectiveness when peritoneal membranes become scarred from repeated bouts of peritonitis.
Blood access is achieved by surgically attaching a native artery (usually in the arm) to an adjacent vein. Over time, the vein enlarges and develops thicker and stronger walls that will accept a dialysis catheter. With this procedure the catheter needle is inserted at the initiation, and removed at the end of each treatment. As an alternative, a section of artificial vessel material (e.g., Gortex) can be used to create a vein-to-vein graft that can be used almost immediately.
Blood is circulated from the patient through a cartridge that contains thousands of tiny tubules (semi-permeable membranes) that are bathed in dialysate (dialysis fluid), which is free of toxins, and whose concentration of electrolytes and minerals are designed to normalize those of the patient.
The advantage of HD over peritoneal dialysis is that is that it is more efficient, requiring only 3 to 4 hours of outpatient treatment 3 times per week. The disadvantages of HD include: Disequilibrium syndrome characterized by headache, weakness and nausea, which is thought to be secondary to rapid removal of uremic toxins. Also, most patients ingest much more fluid between dialysis treatments than can easily be removed and thus require aggressive ultrafiltration (to remove edema fluid). Rapid contraction of the extra cellular fluid compartment can cause low blood pressure, nausea, and vomiting. On occasion, skin bacteria can enter the blood stream, resulting in sepsis, a life-threatening illness requiring rapid diagnosis and treatment.