Dialysis is the process by which the blood is cleansed artificially rather than by the kidneys. The term
dialysis is derived from the Greek word meaning to separate.
During dialysis, metabolic wastes and excess fluids are separated and removed from the patients
blood. There are two types of dialysis :-
Hemodialysis
The first artificial kidney machine was developed in 1943 by Dr.Willem Kolff. Hemodialysis is derived
from two words, hemo, meaning blood and dialysis. Today, it has become the most commonly
performed type of dialysis. Hemodialysis treatments are required three days per week, and each
treatment lasts about four hours.
How it works
During hemodialysis treatment, the patients blood is circulated outside of the body into an artificial
kidney machine, through a link to the patients circulatory system. The blood flows into the dialysis
machine, is cleansed and then returns to the patients body. The dialysis process is continual, with new
blood and dialysate constantly circulating into the machine and waste products and excess fluids
constantly circulating out.The artificial kidney machine contains an internal chamber which is divided by
a thin semipermeable membrance. It is called semipermeable because only particles of a certain size
will pass through it. On one side of the membrane is a special solution called dialysate. On the other
side is the blood which needs to be cleansed. Since red and white blood cells are relatively large, they
will not pass through the pores of the membrane, but waste products (such as creatinine and urea) are
very tiny and will pass through the membrane. Waste products are removed from the blood through
three chemical processes: diffusion, osmosis and ultrafiltration. Diffusion works on the principle that
liquids of different concentrations tend to equalize when placed next to each other. For example, if you
take a cellophane bag and fill it with water mixed with food coloring, seal it and place it in a container of
clear water, you will find in a short time that the clear water will have food coloring in it. The food
coloring has passed through the tiny holes in the cellophane membrane. The water in the bag still has
food coloring in it because the process works both ways.Diffusion continues until there are equal
amounts of food coloring on both sides of the membrane. This state is called equillibrium. Waste
products are found in the patients blood which are not present in the dialysate. During diffusion the tiny
waste particles move out of the blood and into the dialysate until both solutions have reached
equilibrium. By constantly introducing clean batches of dialysate the waste products continue to shift
towards the waste-free dialysate until a large proportion of waste products have been washed out of
the blood. If the patient is low on vital elements, such as calcium or dextrose, they may be added to the
dialysate. Just as the waste products shifted to the side where they were lacking, the calcium and
dextrose will shift towards the side of the chamber where they are needed, the patients blood.
Osmosis is very similar to diffusion, but rather than removing waste products, excess fluid is removed.
To facilitate this process dextrose is added to the dialysate. This works to pull the excess fluid from the
blood.Ultrafiltration is the process by which very minute particles are removed from a substance, in this
case the blood. In order to speed up the removal of excess fluid, a pump may be used. This pump
raises the pressure of the blood flowing through the dialysis machine, there by forcing excess fluids out
of the blood.
Access for Hemodialysis :
In order to be dialyzed there must be a way to connect your circulatory system to the artificial kidney
machine. This connection is called a vascular access and initially requires minor surgery. The fistula is
created by a surgical procedure which attaches a vein to an artery in an arm. This increases the
amount of blood that flows through the vein which in turn causes the vein to enlarge. The larger size of
the blood vesel allows two needles to be inserted for treatment. Because this may cause discomfort,
the skin can be anaesthetised with Novocain. These needles are connected to tubes which go to and
from the artificial kidney machine. A graft also provides access to the patients circulatory system. When
a graft is used, synthetic material is inserted to form a connection between an artery and a vein. The
advantage of the graft and fistula, which both require minor surgery, is that they are under the skin and
therefore less prone to infection than an external shunt. They do require two needle sticks each time
dialysis is performed. Sometimes a person must start dialysis before a permanent access can be
created. In this case, a catheter may be inserted into a vein in your chest, neck or leg to gain access to
the circulatory system. A catheter may also be used if the patient has used up all other possible sites
for a fistula or graft. The advantage of a catheter is that no needles need to be inserted. The
disadvantages are numerous, including the possibility of infection and clotting.
Peritoneal Dialysis
Peritoneal dialysis is usually self administered. In both hemodialysis and peritoneal dialysis, the blood
is cleansed. However, in peritoneal dialysis the process takes place within the patients own body, in the
peritoneal or abdominal cavity, rather than outside the body in a machine. The peritoneum is a thin
membrane which covers the instestines and other contents of the abdominalcavity. During dialysis, the
dialysate is introduced into the abdominal cavity, allowed to stay in for some time, and then drained
out. The peritoneum basically functions the same as the semipermeable membrane used in the artifical
kidney machine. Since it contains a whole network of tiny blood vessels called capillaries, the
peritoneum is constantly able to provide a new supply of blood to be filtered. As blood flows through
the peritoneum, waste products are filtered (through diffusion) and excess fluids are removed (through
osmosis). The wastes flow into the dialysate which remains or dwells within the abdominal cavity for a
variable period of time. At the end of this period the dialysate is drained from the abdomen and fresh
dialysate is introduced.
Access for Peritoneal Dialysis
Access for peritoneal dialysis is gained via a flexible hollow tube, called a catheter, which is surgically
implanted through the wall of the abdomen into the abdominal cavity. This catheter is usually
permanent, but may be replaced as needed. A potential problem with peritoneal dialysis is peritonitis,
an infection of the lining membrane of the peritoneal cavity. The exchanges of dialysis fluid must be
performed using sterile technique in order to prevent this type of infection. Depending on the way
peritoneal dialysis is performed it is described in two different ways:
Continuous Ambulatory Peritoneal Dialysis
Continuous Ambulatory Peritoneal Dialysis (CAPD) is self administered and machine free. CAPD
exchanges are performed in a clean, private location where the patient is comfortable. The process of
exchanging the dialysis fluid is repeated every 4 to 6 hours during the day, with each exchange taking
approximately 30 minutes (10 minutes to introduce and 20 minutes to drain the dialysate). Each day,
the final dialysis is performed right before the patient goes to bed at night. Since the patient is
continually dialyzing, there are usually fewer dietary restrictions. CAPD provides mobility for the patient,
and thus an improved quality of life. The details of an exchange are as follows: Fluid that has been
dwelling in the peritoneal cavity needs to be removed so fresh fluid may be infused and the blood
cleansing process can continue. The catheter is attached to a Y SET. This Y set has a drain bag on
one end and a fresh bag of dialysate on the other. For outflow, the empty bag is placed on the floor
and the used fluid is allowed to drain into it by gravity. When the bag is full, the line is opened clamped
and the inflow line is opened. For inflow, the two litre bag of dialysate is raised above the patients
shoulder and the fresh, warm dialysate is infused by gravity. When that bag is empty, the inflow line is
closed and the Y set and bags are removed and discarded. The patient then resumes normal activity
until it is time for another exchange.
Continuous Cycling Peritoneal Dialysis
Continuous Cycling Peritoneal Dialysis (CCPD) is very similar to CAPD, however, in this case, the
exchanges are performed at night while the patient sleeps. To facilitate this process the patient is
hooked up to an automatic cycling machine. This machine makes several evenly spaced exchanges
during the night and a final one just before the patient gets up in the morning. During the day either
one exchange or no exchanges are made. An advantage of CCPD is that the likelihood of infection
caused by improper handling of the dialysis equipment is reduced. With only one hook-up per day
rather than four or five there is less chance that the patient will introduce some bacteria into the
peritoneal cavity; thus the likelihood of peritonitis is reduced. On the other hand, it is necessary for the
patient to be attached to a machine during the night hours while the CAPD patient remains totally
machine free.
dialysis is derived from the Greek word meaning to separate.
During dialysis, metabolic wastes and excess fluids are separated and removed from the patients
blood. There are two types of dialysis :-
- Hemodialysis
- Peritoneal dialysis
Hemodialysis
The first artificial kidney machine was developed in 1943 by Dr.Willem Kolff. Hemodialysis is derived
from two words, hemo, meaning blood and dialysis. Today, it has become the most commonly
performed type of dialysis. Hemodialysis treatments are required three days per week, and each
treatment lasts about four hours.
How it works
During hemodialysis treatment, the patients blood is circulated outside of the body into an artificial
kidney machine, through a link to the patients circulatory system. The blood flows into the dialysis
machine, is cleansed and then returns to the patients body. The dialysis process is continual, with new
blood and dialysate constantly circulating into the machine and waste products and excess fluids
constantly circulating out.The artificial kidney machine contains an internal chamber which is divided by
a thin semipermeable membrance. It is called semipermeable because only particles of a certain size
will pass through it. On one side of the membrane is a special solution called dialysate. On the other
side is the blood which needs to be cleansed. Since red and white blood cells are relatively large, they
will not pass through the pores of the membrane, but waste products (such as creatinine and urea) are
very tiny and will pass through the membrane. Waste products are removed from the blood through
three chemical processes: diffusion, osmosis and ultrafiltration. Diffusion works on the principle that
liquids of different concentrations tend to equalize when placed next to each other. For example, if you
take a cellophane bag and fill it with water mixed with food coloring, seal it and place it in a container of
clear water, you will find in a short time that the clear water will have food coloring in it. The food
coloring has passed through the tiny holes in the cellophane membrane. The water in the bag still has
food coloring in it because the process works both ways.Diffusion continues until there are equal
amounts of food coloring on both sides of the membrane. This state is called equillibrium. Waste
products are found in the patients blood which are not present in the dialysate. During diffusion the tiny
waste particles move out of the blood and into the dialysate until both solutions have reached
equilibrium. By constantly introducing clean batches of dialysate the waste products continue to shift
towards the waste-free dialysate until a large proportion of waste products have been washed out of
the blood. If the patient is low on vital elements, such as calcium or dextrose, they may be added to the
dialysate. Just as the waste products shifted to the side where they were lacking, the calcium and
dextrose will shift towards the side of the chamber where they are needed, the patients blood.
Osmosis is very similar to diffusion, but rather than removing waste products, excess fluid is removed.
To facilitate this process dextrose is added to the dialysate. This works to pull the excess fluid from the
blood.Ultrafiltration is the process by which very minute particles are removed from a substance, in this
case the blood. In order to speed up the removal of excess fluid, a pump may be used. This pump
raises the pressure of the blood flowing through the dialysis machine, there by forcing excess fluids out
of the blood.
Access for Hemodialysis :
In order to be dialyzed there must be a way to connect your circulatory system to the artificial kidney
machine. This connection is called a vascular access and initially requires minor surgery. The fistula is
created by a surgical procedure which attaches a vein to an artery in an arm. This increases the
amount of blood that flows through the vein which in turn causes the vein to enlarge. The larger size of
the blood vesel allows two needles to be inserted for treatment. Because this may cause discomfort,
the skin can be anaesthetised with Novocain. These needles are connected to tubes which go to and
from the artificial kidney machine. A graft also provides access to the patients circulatory system. When
a graft is used, synthetic material is inserted to form a connection between an artery and a vein. The
advantage of the graft and fistula, which both require minor surgery, is that they are under the skin and
therefore less prone to infection than an external shunt. They do require two needle sticks each time
dialysis is performed. Sometimes a person must start dialysis before a permanent access can be
created. In this case, a catheter may be inserted into a vein in your chest, neck or leg to gain access to
the circulatory system. A catheter may also be used if the patient has used up all other possible sites
for a fistula or graft. The advantage of a catheter is that no needles need to be inserted. The
disadvantages are numerous, including the possibility of infection and clotting.
Peritoneal Dialysis
Peritoneal dialysis is usually self administered. In both hemodialysis and peritoneal dialysis, the blood
is cleansed. However, in peritoneal dialysis the process takes place within the patients own body, in the
peritoneal or abdominal cavity, rather than outside the body in a machine. The peritoneum is a thin
membrane which covers the instestines and other contents of the abdominalcavity. During dialysis, the
dialysate is introduced into the abdominal cavity, allowed to stay in for some time, and then drained
out. The peritoneum basically functions the same as the semipermeable membrane used in the artifical
kidney machine. Since it contains a whole network of tiny blood vessels called capillaries, the
peritoneum is constantly able to provide a new supply of blood to be filtered. As blood flows through
the peritoneum, waste products are filtered (through diffusion) and excess fluids are removed (through
osmosis). The wastes flow into the dialysate which remains or dwells within the abdominal cavity for a
variable period of time. At the end of this period the dialysate is drained from the abdomen and fresh
dialysate is introduced.
Access for Peritoneal Dialysis
Access for peritoneal dialysis is gained via a flexible hollow tube, called a catheter, which is surgically
implanted through the wall of the abdomen into the abdominal cavity. This catheter is usually
permanent, but may be replaced as needed. A potential problem with peritoneal dialysis is peritonitis,
an infection of the lining membrane of the peritoneal cavity. The exchanges of dialysis fluid must be
performed using sterile technique in order to prevent this type of infection. Depending on the way
peritoneal dialysis is performed it is described in two different ways:
- Continuous Ambulatory Peritoneal Dialysis (CAPD)
- Continuous Cycling Peritoneal Dialysis (CCPD)
Continuous Ambulatory Peritoneal Dialysis
Continuous Ambulatory Peritoneal Dialysis (CAPD) is self administered and machine free. CAPD
exchanges are performed in a clean, private location where the patient is comfortable. The process of
exchanging the dialysis fluid is repeated every 4 to 6 hours during the day, with each exchange taking
approximately 30 minutes (10 minutes to introduce and 20 minutes to drain the dialysate). Each day,
the final dialysis is performed right before the patient goes to bed at night. Since the patient is
continually dialyzing, there are usually fewer dietary restrictions. CAPD provides mobility for the patient,
and thus an improved quality of life. The details of an exchange are as follows: Fluid that has been
dwelling in the peritoneal cavity needs to be removed so fresh fluid may be infused and the blood
cleansing process can continue. The catheter is attached to a Y SET. This Y set has a drain bag on
one end and a fresh bag of dialysate on the other. For outflow, the empty bag is placed on the floor
and the used fluid is allowed to drain into it by gravity. When the bag is full, the line is opened clamped
and the inflow line is opened. For inflow, the two litre bag of dialysate is raised above the patients
shoulder and the fresh, warm dialysate is infused by gravity. When that bag is empty, the inflow line is
closed and the Y set and bags are removed and discarded. The patient then resumes normal activity
until it is time for another exchange.
Continuous Cycling Peritoneal Dialysis
Continuous Cycling Peritoneal Dialysis (CCPD) is very similar to CAPD, however, in this case, the
exchanges are performed at night while the patient sleeps. To facilitate this process the patient is
hooked up to an automatic cycling machine. This machine makes several evenly spaced exchanges
during the night and a final one just before the patient gets up in the morning. During the day either
one exchange or no exchanges are made. An advantage of CCPD is that the likelihood of infection
caused by improper handling of the dialysis equipment is reduced. With only one hook-up per day
rather than four or five there is less chance that the patient will introduce some bacteria into the
peritoneal cavity; thus the likelihood of peritonitis is reduced. On the other hand, it is necessary for the
patient to be attached to a machine during the night hours while the CAPD patient remains totally
machine free.
DIALYSIS
Balaji Medical and Educational Trust
| Chronic Kidney Failure is one of the Deadliest disease. Yet, it is least understood. |
| Dr.Rajan Ravichandran MD,MNAMS,FRCP(Edin),FACP(USA) Nephrologist |
 |
|