When kidney function declines to the point of failure, dialysis becomes a necessary treatment. This process removes excess fluids, waste products, and toxins from the blood, functions normally handled by healthy kidneys. The purpose of dialysis is to restore a balanced internal environment within the body, preventing complications associated with kidney failure. There are two fundamentally different methods of dialysis available to patients: Hemodialysis and Peritoneal Dialysis.
The Two Primary Dialysis Methods
The two main types of dialysis are distinguished entirely by where and how the blood is filtered, using different parts of the body or external equipment. Hemodialysis cleans the blood outside the body using a machine, while Peritoneal Dialysis uses a natural filter located inside the body. The choice between these methods depends on the patient’s medical condition, lifestyle, and personal preferences.
Hemodialysis (HD) involves drawing the patient’s blood out of the body through a vascular access point, such as an arteriovenous fistula or graft, typically created surgically in the arm. The extracted blood is then pumped through an artificial kidney, called a dialyzer, which acts as a filter. Inside the dialyzer, the blood flows on one side of a semipermeable membrane while a cleansing fluid called dialysate flows on the other side.
Waste products, excess salts, and fluid move across this membrane from the blood into the dialysate through processes like diffusion and ultrafiltration. Diffusion is the movement of solutes from an area of higher concentration (the blood) to an area of lower concentration (the dialysate), removing toxins like urea and creatinine. Ultrafiltration uses pressure to push excess fluid from the blood across the membrane.
Peritoneal Dialysis (PD), conversely, uses the body’s own peritoneal membrane, which lines the abdominal cavity, as the natural filter. A soft, hollow tube called a catheter is surgically placed into the abdomen to allow the exchange of fluids. The process begins when the dialysate solution is introduced into the peritoneal cavity through this catheter.
While the dialysate dwells inside the abdomen, the peritoneal membrane, which is rich in tiny blood vessels, facilitates the exchange. Waste products and excess fluid from the blood pass across the membrane into the dialysate, again driven by diffusion and osmosis. After a prescribed dwell time, the fluid, now containing the removed waste, is drained out of the body and discarded, completing one exchange cycle.
Variations in Hemodialysis Treatment
While the core mechanism of using a dialyzer remains consistent, hemodialysis treatment is administered in several ways that differ in location, frequency, and duration. The most common form is In-Center Hemodialysis, where a patient goes to a specialized clinic typically three times per week for a session lasting about three to four hours. This standard schedule is administered entirely by trained medical staff, providing a fixed, supervised routine for treatment.
A more flexible option is Home Hemodialysis (HHD), which allows patients to perform their treatments in their own residence after comprehensive training. HHD is often done more frequently than the in-center schedule, sometimes five to seven days a week, with sessions that can be shorter, lasting between two and four hours. The increased frequency of shorter sessions can lead to a gentler fluid removal and better overall toxin clearance, closely mimicking the continuous function of native kidneys.
Nocturnal Hemodialysis represents a specific variation focused on extended treatment duration, usually lasting six to eight hours per session. This longer, slower treatment is performed while the patient sleeps, allowing for a more thorough and gentle purification process. Nocturnal treatment can be done either at home, requiring a trained care partner and specialized equipment, or in a dedicated in-center facility that offers overnight shifts.
The extended duration of nocturnal sessions is associated with significant benefits, including fewer dietary and fluid restrictions for the patient. The gentle removal of fluid and waste over a longer period reduces the risk of complications such as sudden drops in blood pressure and muscle cramping that can occur with shorter, more intense treatments. This approach maximizes treatment efficacy while minimizing the interruption to the patient’s daytime schedule.
Variations in Peritoneal Dialysis Treatment
Peritoneal dialysis is primarily categorized into two types, which are defined by the method used to manage the fluid exchanges and the resulting impact on the patient’s daily routine. Continuous Ambulatory Peritoneal Dialysis (CAPD) is a manual, machine-free process performed by the patient or a caregiver during waking hours. This method requires the patient to perform three to five exchanges daily, with each exchange typically taking about 30 to 40 minutes.
During a CAPD exchange, a bag of fresh dialysate is connected to the abdominal catheter, and gravity is used to drain the spent fluid before infusing the new solution. The fluid then remains in the peritoneal cavity for a prescribed dwell time while the patient goes about their normal activities, giving it the “ambulatory” designation. Because the peritoneal cavity is always filled with fluid, it provides continuous, steady waste removal throughout the day.
Automated Peritoneal Dialysis (APD), also known as Continuous Cycling Peritoneal Dialysis (CCPD), uses a machine called a cycler to manage the fluid exchanges. This process is typically performed overnight while the patient sleeps, minimizing the disruption to daytime activities. The cycler machine automatically drains the used fluid, fills the peritoneal cavity with fresh dialysate, and repeats this cycle multiple times over a period of about eight to ten hours.
In APD, the patient is connected to the cycler machine at night, allowing for greater freedom during the day compared to the manual exchanges required by CAPD. In some cases, a patient may still perform a single exchange during the day to ensure adequate clearance, a variation known as tidal or day-dwell APD.