Dialysis

Dialysis is a type of kidney replacement therapy that removes metabolic waste products, toxins, as well as excess fluid and electrolytes from the blood. Most often, dialysis is required due to end-stage renal disease, which means the kidneys have lost almost all their function. Dialysis can also be used to correct fluid, acid-base, and electrolyte imbalances, and to treat drug overdoses. The two types of dialysis are hemodialysis and peritoneal dialysis.

Now, to perform dialysis, either vascular access for hemodialysis, or abdominal access for peritoneal dialysis will be needed. So, for hemodialysis in an acute setting, temporary venous access can be obtained through a catheter in the internal jugular or femoral vein. When permanent access is needed for long-term hemodialysis, an arteriovenous or AV fistula or graft is created surgically in the patient’s arm. This creates a connection between a small artery and a vein, which causes the vein to become “arterialized,” meaning it increases in size, develops thicker walls, and blood flow is increased.

Peritoneal access can be obtained by inserting a catheter into the peritoneal cavity.

Okay, let’s look at the principles of dialysis, which include diffusion, osmosis, and ultrafiltration. Diffusion is the movement of solutes from a greater concentration to a lesser concentration until the two solutions have the same concentration of solutes on either side of a semipermeable membrane. Osmosis is the health education platform that makes learning easy and fun, but in this case, it refers to the movement of fluid through a semipermeable membrane from an area of lesser solute concentration to an area of greater solute concentration. For example, glucose creates an osmotic gradient across a membrane and is able to pull fluid through that gradient. Finally, ultrafiltration is when a driving pressure moves fluid and solutes across a semipermeable membrane.

Now, to understand how hemodialysis works, let’s look at the dialysis machine. One of the most important components is the dialyzer, which acts like an artificial kidney. The dialyzer has two compartments separated by a semipermeable membrane: a blood compartment and a compartment containing the dialysis solution, called the dialysate. Dialysate is typically composed of water, electrolytes, glucose, and a buffer, like bicarbonate. The semipermeable membrane allows the movement of small and medium-sized molecules like electrolytes, urea, and creatinine to move from the patient's blood into the dialysate while preventing the movement of larger plasma components like proteins and blood cells.

Other parts of the dialysis machine include a pump to help draw blood from the patient; a heparin infusion pump, since anticoagulation is needed due to the risk of blood clots; and an air trap or a sensor to detect air bubbles so they can be prevented from getting into the circulation.

When the patient is connected to the dialysis machine, their blood is pumped through the tubing where heparin is added. Once the blood reaches the dialyzer, metabolic wastes and toxins, as well as excess fluid and electrolytes are drawn into the dialysate. The cleansed, dialyzed blood is returned to the patient, and the used dialysate is drained and discarded.

Next, let’s look at peritoneal dialysis, which uses the patient’s own peritoneal membrane as the semipermeable membrane. Dialysate is introduced in the abdominal cavity through the abdominal catheter, and dwells in the peritoneal space for a certain amount of time, usually 4 to 6 hours. During this time, metabolic wastes and toxins, as well as excess fluid and electrolytes are filtered through the peritoneal membrane and drawn into the dialysate. Afterwards, the dialysate is drained and discarded.

Okay, let’s look at the care you’ll provide for a patient undergoing dialysis. Start by checking their pretreatment laboratory test results and assessing their weight and vital signs. Auscultate their heart and lung sounds and look for the presence of edema.