[scientizscht (OP)]

How peritoneal dialysis works?

[chris]

Dialysis is indicated when a person's own kidneys fail; in an acute setting, and in chronic kidney conditions where other options may not be suitable, this is usually acheived by placing a tube into a large blood vessel and pumping blood through a partially permeable filter system that uses osmotic and concentration gradients to equilibrate and correct the blood biochemistry.

This sort of process is very invasive, takes a long time and is therefore inconvenient for the patient. Therefore, where the process needs to be carried out in the long term, doctors often elect to do continuous ambulatory peritoneal dialysis (CAPD) as an alternative, at least for a while.

In simple terms, a catheter with a tap on the end is implanted into the abdominal cavity to provide a route between the outside world and the space around the internal organs.

The patient connects this catheter to a large bag of dialysis fluid with the correct biochemical composition to correct their blood chemistry. The fluid runs into the peritoneal cavity and sits there. The patient disconnects the tap and then goes about their business. Meanwhile, the body exchanges ions and water across the membranes of the internal abdominal organs over a period of hours with the infused dialysis fluid.

After a set period of time, the patient re-opens the tap, drains out the spent fluid and then replaces it with fresh. With regular biochemical monitoring, and checks and care to avoid infection, this can be a safe and convenient mode of dialysis for many patients. Yes, the patient walks around with some extra fluid inside them, and they have a tube running into their abdomen so they need to be careful what they do to avoid trauma or infection, but on the whole this is a safe and well-tolerated procedure.

Regrettably, it is not, however, an indefinite option. With time, the peritoneal membranes thicken and develop adhesions in response to the low-grade irritation imparted by the presence of the dialysis fluid. This impairs the effectiveness of the dialysis process, eventually rendering it inadequate. It also carries a risk of other complications such as intestinal obstruction and infection.

At this point, patients normally need to move onto haemodialysis, where blood is piped to a machine for filtering. To facilitate this, a fistula is normally fashioned between an artery and a vein in one arm to provide a high-flow system so that large volumes of blood can be obtained and returned to the body rapidly to minimise the time spent on dialysis.

All of these processes take a heavy toll on a person's health and their well-being. It's also extremely expensive. As such, and where possible, patients are transplanted with a healthy kidney to free them from the burden.