Author: Kamal D. Shah
(Acknowledgements: A. Shukla for reviewing the draft and suggesting improvements.)
If you are on Peritoneal Dialysis, you should understand the components of your PD prescription. Each aspect of the prescription indicates some part of your overall treatment. If you understand the significance of the parameters, you can have a more informed discussion with your doctor about how to make the treatment work for you.
Here are some of the parameters you should be aware of:
1. CAPD or CCPD or a hybrid
The type of PD you are on is probably the first thing that you should be aware of. CAPD stands for Continuous Ambulatory Peritoneal Dialysis. CCPD stands for Continuous Cyclic Peritoneal Dialysis. CCPD is also called APD or Automated Peritoneal Dialysis. The type of PD basically indicates whether you are doing exchanges in the day or the night.
If you are on CAPD, it means you do your exchanges during the day. Most people do three or four exchanges during the day. These exchanges are done manually without the aid of a machine.
CCPD or APD is usually done at night with the help of a machine called a cycler. You connect your transfer set to the PD tube and once you set up the bags and the kit on the machine, the machine takes care of the rest.
Some people do CCPD with one manual exchange during the day to get better clearance or ultrafiltration.
2. Number of exchanges
The number of exchanges tells you how many bags of PD fluid go in and out of your body. Typically one exchange means you drain out the old fluid and infuse one bag of fresh fluid in. The more the number of exchanges, the better the clearance of toxins. This is because with time, the fluid in the Peritoneal Cavity becomes saturated with toxins and its ability to pull out toxins from the blood reduces. So infusing fresh fluid improves the clearance.
Most people do three or four exchanges a day. Some people are advised to drain out fluid before they go to bed at night while others are advised to keep fluid inside them at night.
3. Type of PD Fluid
There are two main types of PD fluid available these days – Dextrose based and Icodextrin based. Dextrose is the most common and is usually cheaper than Icodextrin. Icodextrin has some advantages over dextrose. It can pull off more fluid and does not harm the Peritoneal Membrane like Dextrose does. It also does not load the body with Glucose like Dextrose does. However, Icodextrin can pull off a lot of fluid from the blood and there is a risk of low Blood Pressure and low Sodium levels.
If you are unable to get good ultrafiltration using dextrose, you should talk to your doctor about the possibility of using Icodextrin for one exchange instead of Dextrose.
4. Concentration of Fluid
The next thing you need to know about is the concentration of the PD fluid in the bags. While Icodextrin usually comes in a single concentration (7.5%), Dextrose comes in different concentrations. Again, different PD fluid manufacturers provide slightly different concentrations. The most commonly used concentrations are around 1.5%, 2.5% and 4.25%.
Remember, the higher the concentration, the more the fluid that can be removed (ultrafiltration). Lower concentrations means lower removal of fluid. One important factor to remember is that higher concentration of PD fluid means more Glucose load on the body and also higher the damage to the membrane.
That is why, generally, doctors advise the lowest concentration of fluid that is possible to achieve reasonably good ultrafiltration.
5. Dwell Time
Dwell time is the duration when the fluid stays in the Peritoneal Cavity in your abdomen. This has an important bearing on removal of toxins and fluid from your body. The dwell time needs to be decided carefully. Too short and too long dwell times can both be a problem. Too short dwell times would mean that you need to do more exchanges to achieve the desired ultrafiltration and clearance. Too long dwell times would mean that not enough ultrafiltration and clearance happen as the fluid would reach saturation and lie there doing nothing and worse, continue to load your body with glucose and damage your peritoneum. It would also start pushing toxins and fluid back into your body. Icodextrin has the benefit of allowing a long dwell without reverse flow of fluid and toxins.
The dwell time is usually set after determining the type of your Peritoneal Membrane. Some membranes do better with short dwell times while others do better with longer dwell times.
6. Nature of membrane
This is not a part of your PD prescription. However, it is important to know what this means and how it is important for your treatment. The nature of your Peritoneal membrane is usually determined by a test called the Peritoneal Equilibration Test (PET). It involves collecting blood samples, doing a few exchanges and collecting samples of the drain fluid as well. The result of this test is usually one of Low, Low Average, High Average or High. Generally Low and Low Average means that your Peritoneal Membrane transports solutes and fluids at a low rate. High and High Average means that your membrane transports toxins and fluids at a high rate. The rate of transport is in increasing order is Low, Low Average, High Average, High.
Low and Low Average Transporters need longer dwell times because the membrane needs longer durations to transfer toxins and fluid from the blood into the fluid in the Peritoneal Cavity. High and High Average Transporters need shorter dwell times becomes the membranes allow for rapid transfer of toxins and fluid into the Peritoneal Dialysis fluid. Keeping the fluid in longer results in reverse flow of fluid and toxins.
These are the main aspects you need to be aware of with regard to Peritoneal Dialysis. Remember, if you are proactive about your treatment, you can have an intelligent discussion with your doctor and help them help you get the best out of your treatment.