I’m starting my fourth week of peritoneal dialysis at home and I thank all the people who have wished me good luck on my new venture. And a number have asked me to explain how it works.

Of course, I’m not in any way an expert and I’m relying on the PD patient directory for an accurate description of the procedure. It is one of several ways to treat kidney failure but it is close to the natural function of the kidneys. It rids the body of waste products, extra fluid and helps balance chemicals in a slow and gentle way.

This type of dialysis relies on a membrane with pores (tiny holes) which filters waste products from the blood. In order to work, the membrane has to be semi-permeable. This simply means that waste products will pass through, but that the products needed to keep your body functioning will not.

This type of dialysis uses the peritoneal membrane as an artificial dialysis and it lines the abdominal cavity, covering most of the internal organs. The membrane has a number of small blood vessels (capillaries) and when the dialysis solution flows into the peritoneal cavity, waste products and excess fluid transfers from the blood into the dialysis fluid. Three processes, osmosis, diffusion, and ultrafiltration complete the procedure.

Osmosis allows excess water to be removed from the blood, with the body attempting to balance the water on both sides of the membrane. Water will transfer from an area with the largest amount of (most concentrated) to a section with the smallest amount (less concentrated).

You make the exchange four times in a 24 hour period, first draining the solution out of your body and allowing the new dialysis solution into your body. The solution contains dextrose, a simple sugar. The sugar actually draws excess fluid from your blood into the dextrose solution. The extra water in your blood will infiltrate into the dialysis solution, having moved through the membrane.

The diffusion process removes waste products and extra chemicals. The dialysis solution is clear of waste products and contains the proper amount of chemicals. Waste products and extra chemicals are drawn from the blood into the dialysis solution until they are equal. Once this occurs, the dialysis is over. 

An extra amount of water is removed during the dialysis process and this is called ultrafication. The process is done in PD by using a dialysis solution with an extra increased concentration of sugar. The higher concentration of sugar, the more water will be removed from your blood.

The solution used in PD dialysis comes in three strengths, 1.5 percent dextrose, 2.5 percent dextrose and 4.25 percent dextrose.

As I have chronicled in my journey into home dialysis, a soft plastic tube, a catheter, was surgically implanted into my abdomen and an exchange is the process of draining the peritoneal cavity of any old dialysis solution. And then allowing the new solution to flow into your abdomen.

When the medical staff checks your vital signs, they tell what strength of dialysis solution to use. The first week I alternated between 1.5 percent and 2.5 percent and the second week, it was three exchanges of 2.5 percent and one 1.5 percent during the four exchanges in the 24 hour period.

My exchange schedule is roughly 8 in the morning, 12 noon, 4 in the afternoon and 8 at night. The solution on the evening exchange remains in my body until the next morning.

Now, I must admit that while reading this for typos (as I grow older ”“ 87 in July) my arthritic fingers aren’t as accurate on the keyboard as my younger days ”“ I thought it had the tone of my years as a college lecturer and not journalism. But, then, in a column, you are allowed a certain freedom to express yourself.

If you have a question or comment, I have a new e-mail address: georgedouglas@fairpoint.net.

— George Douglas writes regularly about his experiences as a kidney dialysis patient. He is the former editor of the Boston Post. He lives in Kennebunk.