Getting a grasp of peritoneal dialysis

In this video, we'll take an in-depth look at how peritoneal dialysis works, how it differs from hemodialysis, some important considerations when using it, and which patients should not be using peritoneal dialysis.

Daphne H. Knicely, MD MEHP
Daphne H. Knicely, MD MEHP
3rd Feb 2020 • 4m read

Peritoneal dialysis is an alternative option to hemodialysis. In this video, from our Dialysis Essentials course, we'll take an in-depth look at how peritoneal dialysis works, how it differs from hemodialysis, some important considerations when using it, and which patients should not be using peritoneal dialysis.

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Video transcript

An alternative option to hemodialysis is peritoneal dialysis, patients must have a personal dialysis catheter placed into their abdominal cavity. The catheter is placed one month before starting peritoneal dialysis so the area can heal. The abdominal cavity is covered in small capillaries, and these capillaries act as filters. Through the peritoneal dialysis catheter, dialysis fluid is instilled into the abdomen.

The fluid sits in the abdomen for several hours allowing for chemistries to be balanced, toxins cleared and fluid to be removed from the blood in the capillaries. This is based on the concentration gradients between the peritoneal fluid in the blood. Then the peritoneal fluid is drained from the abdomen and discarded, new fluid is instilled and the process starts over.

There are three major layers of the peritoneal membrane, the mesothelial layer, the interstitial space and the capillary endothelial The mesothelial layer provides minor resistance to the flow of toxins. The major barrier to solid transport is the capillary endothelial. The capillary endothelial cells have three types of pores that allow movement of water and soil use. aquaporins allow water across the cell membrane and they are stimulated by the osmolality of the dialysate.

The small pores transport small solids such as urea, creatinine and electrolytes. The large pores transport larger macromolecules, such as proteins, there's a higher density of aquaporins in small pores compared to large pores. Similar to hemodialysis. The movement of water and salt use occurs by two processes, diffusion and convection.

Diffusion is the main mechanism of small salt transport and peritoneal dialysis. diffusion is dependent on peritoneal membrane surface area, the salt concentration gradient between the blood and the dialysate the dwell time of the dialysate in the period In your cavity in the Dallas eight flow rate, solids are transported from the blood to the Dallas, or the Dallas eight to the blood depending on the concentration gradients.

For example, there is no urea or creatine and in the Dallas eight, but there are high concentrations in the blood and in stage renal disease. So urea and creatinine will move from the blood into the dialysate. The dextrose concentration in the dialysate is much higher than that of glucose in the blood.

So that will move down its concentration gradient into the blood. smaller molecules will diffuse faster than larger molecules. The fusion of solids and peritoneal dialysis can vary from patient to patient and is determined by the degree of vascularization in the amount of inflammation present in the peritoneal membrane.

Remember, ultrafiltration is the movement of fluid across the peritoneal membrane in response to osmotic forces. Convection occurs as dextrose in the dialysis creates an osmotic force that causes water to move from the blood into the dialysate. With the water dissolve small solids move from the blood into the dialysate by solvent drag. ultra filtration uses both aquaporins and small pores. We can modify the amount of ultra filtration that occurs by changing the dextrose concentration in the peritoneal dialysate.

The higher the dextrose concentration, the greater the ultra filtration. Over time the dextrose in the dialysate will diffuse across the capillary membrane in the osmotic gradient will dissipate. It's worth mentioning that there is also lymphatic absorption from the peritoneal cavity. The lymphatic transport rate is about two liters per day.

It's usually negligible unless there's a problem with the lymphatic system. So the net fluid removal and peritoneal dialysis is the ultrafiltration osmotic forces minus lymphatic absorption. Peritoneal dialysis only takes place at home unlike home hemo dialysis patients don't need a partner to perform the dialysis. It's usually done daily.

Peritoneal dialysis can be done two ways through manual exchanges known as continuous ambulatory peritoneal dialysis, or overnight through a cycler known as automated peritoneal dialysis. There is no morbidity or mortality difference in preferences based on the patient's lifestyle. Some patients are not candidates for peritoneal dialysis, such as those with abdominal cancers, those with ventriculoperitoneal shunts and those who have had major abdominal surgeries, because scar tissue can limit peritoneal filtration.

There are some benefits to peritoneal dialysis. The fluid removal is usually gentler than haemodialysis, which prevents intradialytic hypotension. The blood pressure tolerates the fluid removal because the dialysis is done daily and fluid is removed at a slower rate. Also due to daily dialysis sessions the diet is less restrictive.

There are some disadvantages to peritoneal dialysis, such as the need to have a home with space for all the equipment and supplies. Also, the dialysis solution typically contains a lot of dextrose which can be an issue for diabetic patients, but this can be managed by adjusting insulin dosages.