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From time to time, I have noticed some questioning and uncertainty arising at the Home Dialysis Central Facebook site regarding the difference between, relative place of, and effective efficiency of the two main dialysis therapies: peritoneal dialysis (PD) and haemodialysis (HD) – especially as theses factors apply in the home. Many who respond clearly do understand this, but some still seem a little hazy. I thought it might be useful to pick through some of the myths and legends about both, and put them in context.
Firstly, one of the two therapies is exclusively a home therapy (PD), while HD, though in my view best performed at home, is most commonly still offered as a facility-based treatment. I do not intend to pick over the bones of the “at home” versus “at facility” argument here—that has been the subject of several previous blogs and is a theme that runs strongly though most of the views expressed at this site. Rather, I seek to concentrate on some of the practical differences between the two options.
Firstly, there is the efficiency of dialysis. PD uses a natural, inbuilt body “membrane”—the peritoneum—a layer of mesothelial cells a single cell width thick, that line the internal cavity in which lie our internal abdominal organs. I ask my patients if they have ever opened the belly of a fish, or animal…most will certainly have at the least slit open a fish…and have seen the silver shiny membrane that lines the belly cavity inside. This same peritoneal membrane also extends to cover all of the internal abdominal organs. Underlying this membrane is a myriad of small, blood-carrying capillaries (microscopic blood vessels) that carry the blood and the wastes, impurities, and extra water it contains, and that would normally be removed by healthy kidneys, up close to the under-surface of this thin shiny membrane. We are built no differently to a fish, or any other animal. Opened up, the inner lining of a human belly shines and glistens too.
The principle of PD is to instil a specially formulated fluid into the belly cavity so that it can interact with and remove water and solutes from the blood in these peritoneal capillaries, with the peritoneal membrane acting as a separating, but permeable “divider” between blood and the dialysis fluid…just like the artificial membrane of a haemodialyser does.