Peritoneal Dialysis

For fill volume, it is the amount of dialysis fluid that you fill into the peritoneal cavity. In general, one starts at a smaller fill volume to avoid leakage of dialysis fluid around the catheter. So we usually start with 5 milliliters per kilo of fill volume and can go up slowly depending on the size of the patient. The usual final goal of the fill volume is 20 to 45 milliliters per kilogram. Again you have to be very careful in how quickly you fill and how large the volume is, as the more volume put into the peritoneal cavity, the higher chances of leakage around the catheter site which leads to the risk of infection as well as poor efficacy of peritoneal dialysis. Other things to consider when you are determining the fill volume is not only the size of the child but does the child have any pulmonary disease. If you fill too much volume in the peritoneal cavity or the abdomen will push up on the diaphragm and the patient may have difficulty breathing. It is important to check with the hospital policy on the maximum goal fill volume as the level may vary among institutions                      

We all know home is where the heart is, so many people do dialysis at the comfort of their home on their schedule, no need to leave family or miss the pets. A couple of trips a month to the dialysis center for help from the experts. Home dialysis can give people more freedom and time to enjoy life. Considering the factor, the majority of kidney doctors say they choose to do dialysis at home if they have kidney failure as they know what is best. The most popular dialysis in the US is peritoneal dialysis often just called the PD. It was invented in the days of bell-bottom and rock and roll, so it had 40 years to be perfected. Today more than 45,000 people in the US do PD. To do a PD you need an access pore called the PD catheter near your belly button. Getting this catheter requires minimal invasive surgery most people go home the same day. A typical day in your home when doing PD using an At Home machine, before going to bed in the evening putting on the favorite PJ, carefully connect your PD machine to the PD catheter. Program the treatment by pressing a couple of buttons, then go to bed and try going to sleep. This routine takes less than 15 minutes, after getting 8 to 10 hours of sleep wakeup and disconnecting the machine that’s about it. You are now ready to go on with your daily life activities, you can work, visit friends, exercise, enjoy your hobbies and even travel. When you are ready for bed, you just need to repeat the procedural routine.

There is also a way to do a PD by hand if you are interested your doctor will describe how this process works. So now we think what’s the catch, like all medical treatments there are some considerations. PD requires you do the dialysis treatment on your own or with a partner. Your dialysis center will give you all of the training you need. Also, PD requires supplies, so you will need a place to store them and sometimes you can get an infection. But this can usually be treated with medications outside of the hospital. While there are considerations PD has many benefits. PD is an effective treatment, it cleans the blood every day while the hemodialysis cleans the blood 3 times a week. PD is also gentler on the body including the heart, plus some people have a little kidney function remaining when starting dialysis, PD can help keep it going. PD works around your life schedule, this means more time doing the things you love. So you can catch life’s moments big or small, even the diet is less restricted. It is important to remember that PD is just one of the many different treatment choices, including transplants, in-center hemodialysis, and home hemodialysis. How you do dialysis is a big decision, it makes a huge impact on your life. No-one chooses kidney disease, but how you treat it is a choice you get to make with your doctor. This is an opportunity for you to take back some control.  

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Principles Behind PD

PD involves the use of the peritoneal membrane to do 3 things

  1. Remove fluids, we call that ultrafiltration.

  2. Restore the balance of blood chemistries.

  3. Filter waste products.

This requires a mixture of fluids and electrolytes to perform this dialysis. And this type of mixture of fluid and electrolytes is called peritoneal dialysis fluid. Few more concepts before we go into detail of the PD

  1. Osmosis 

Osmosis is the movement of water across a membrane, in this case, it would be peritoneal membrane from the areas of low solute concentration to areas of high solute concentration. 

  1. Diffusion

Diffusion is the movement of molecules across, again, and again, in this case, the membrane is the peritoneal membrane from the areas of high concentration to areas of low concentration. So these molecules such as electrolytes, sodium, potassium, creatinine, albumin, urea also medications, and even toxins. 

  1. Ultrafiltration (UF)

This is a very important concept, this is how much water you want to remove. Ultrafiltration is calculated by volumes removed minus volumes filled. For example, if your fill volume is 100 milliliters and the amount you removed is 150 milliliters. Then the ultrafiltration is 150 milliliters minus 100 milliliters. So you can say you have actually removed a net negative of 50 milliliters. It is absolutely important when you do peritoneal dialysis that you establish accurate tables to log these volumes because you will have different volumes to fill and drain. What you really want to measure is the net removal of the fluid. Some factors affecting ultrafiltration are 

  • Dextrose is what we use to pull the water out because of the concept of osmosis. So higher dextrose concentration will allow for more water removal. 

  • If you increase the dwell time, the amount of time fluid is in the peritoneal cavity that will also allow for more water removal.    

  • Finally, if you increase the fill volume the amount of fluid that you put into the peritoneal cavity, that will also allow for larger water removal or increase ultrafiltration. If you want to decrease ultrafiltration, considering you are removing too much fluid too quickly and you start to worry about hemodynamic instability, then you can decrease the dextrose concentration, decrease the fill time and decrease the dwell time.

Dialysis Setup 

Fill Time

This is the time you allow the peritoneal dialysis fluid filled into the peritoneal cavity. Usually, the time taken is 5 to 10 minutes.

Dwell Time

This is the time you leave the peritoneal dialysis fluid into the peritoneal cavity. Usually, this takes about 35 to 40 minutes. Sometimes it is easier to combine the 2 together the fill time and the dwell time especially if you don’t have any machine available to pump the fluid in. And then you can set the whole fill time as 45 to 50 minutes. If it is a larger patient then a good dwell time would be 2 hours.

Drain Time 

This is the amount of time required to remove the dialysis fluid from the peritoneal cavity. Usually, this is set at 10 minutes, again the longer you set the drain time the more fluid you can remove. So the cycle includes the fill time, the dwell time, and the drain time as we call exchanges. 

Now considering the factors to remove molecules because the peritoneal dialysis is not only water removal but also molecule removal. The way to remove molecules is dependent again on diffusion. So molecules that are very small will move much quicker than the molecules that are very large. So the size of the molecule will affect the removal rate or the efficacy of that molecule. For example, a small molecule could be creatinine, for example, a larger molecule would be albumin. Fortunately in general, peritoneal dialysis is used when the patients have renal failure. This means they have an accumulation of urea and creatinine, those are the ones that need to be removed. Therefore those occur very quickly, it does not take much time. You will get excellent removal with peritoneal dialysis even with 1-hour and 2-hour cycles. Also, the concentration gradient of the molecule, if you put a lower concentration of for example sodium into the dialysis fluid and let’s say the patient’s sodium level is about 160 milliequivalents per liter then there will be greater removal of sodium into the dialysis fluid. If you increase the volume of the peritoneal dialysis fluid in the peritoneal cavity so the fill volume is increased, you will also allow for more removal of molecules. if you increase the dwell time, you allow for more removal of molecules. Finally, if you increase the drain time, hopefully, you will drain more fluid. And therefore you will increase the removal of molecules.

Peritoneal Dialysis Fluid

The fluid is made up of components such as 

  1. Water

  2. Dextrose, which is the osmotic agent  

  3. Buffers such as acetate, lactate, bicarbonate 

  4. Electrolytes, sodium, potassium, calcium, magnesium, chloride

  5. Medications, in some cases

There are many commercially available dialysates as we call them with standard amounts of dextrose and sodium. Often these dialysate bags do not contain potassium as one usually wants to remove potassium in renal failure. However, if we do not have the availability for the standardized bags then one can make dialysate bags of their own. Let us see 2 examples of dialysate bags that can be easily made, both of these will give you 1-liter volume.     

  1. The first one includes 680 milliliters of normal saline plus 320 liters of D5 % dextrose and 5 milliliters of D50 dextrose. 

  2. The second one you need to add 40 milliliters of sodium bicarbonate plus 680 milliliters of normal saline plus 280 milliliters of D5 % or dextrose 5 % plus 5 milliliters of dextrose 50 % and you can also add some gentamicin. That will give you again a total of 1-liter of dialysis bag.

We need to check with the institution policy on how to create a bag of dialysate for your hospital. 

Peritoneal Dialysis In Practice

Let us first talk about the peritoneal dialysis protocol, 

  1. The first thing is determined is the fill volume. If the catheter is placed immediately and peritoneal dialysis needs to be performed, then the recommendation is that small fill volumes be started to avoid leakage. 

The next is to determine fill time, again by gravity or manual peritoneal dialysis, fill time is about 5 to 10 minutes. The next is then to set the dwell time, again the longer you dwell theoretically the more water you remove and the more molecules you remove. If you are going to have a 1-hour cycle, then a good dwell time would be 40 to 45 minutes. If you are going to do a 2-hour cycle then the dwell time is 100 to 105 minutes. Similarly, if you are going to do a 3-hour cycle, then a good dwell time would be 160 to 165 minutes. The next is to determine the drain time, in a 1-hour cycle usually the drain time is about 10 minutes.

  1. The next thing to do is to record the ultrafiltrate, then we will check the electrolytes. This is especially important in the initiation of peritoneal dialysis. A recommendation is to check every 2 to 4 hours, after that once it is routine one can check once a day or twice a day depending upon the resources available.  

  2. The next is to assess the ultrafiltrate, the net removal of water. Once you start peritoneal dialysis periodically you need to re-assess, do you want to increase ultrafiltrate or do you want to decrease.

  3. The next is to weigh the patient daily, this is very important as this is how they determine patient fluid status as we are the ultrafiltrate.

  4. The next thing to do is check for blood pressures frequently, especially in the initiation of peritoneal dialysis. If you have an increase or very efficacious ultrafiltration there is a risk of causing hypotension. 

  5. Moving on if you have to temporarily discontinue peritoneal dialysis, it is very important to keep the catheter site clean. So the steps to this one are to completely drain the peritoneal dialysis fluid. Then to fill with new peritoneal dialysis fluid, but only 50 % of your fill volume. So you don’t want to fill this completely but you want to leave a little bit fluid into the peritoneal cavity. This will allow the catheter to flow freely into the peritoneal cavity and prevent it from touching other organs which can cause blockage and complications of peritoneal dialysis in the future. 

It is very important to the amount of peritoneal dialysis fluid inserted during the temporary discontinuation may vary among institutions.

FAQ (Frequently Asked Questions)

1. What are The Advantages of Peritoneal Dialysis?

The advantages of peritoneal dialysis include 

  • This is a very gentle way of removing fluid as well as molecules, so for patients who have hemodynamic stability peritoneal dialysis is very safe.

  • Slow correction of metabolic imbalances, so the risk of dropping serum sodium too low is less likely with peritoneal dialysis. In general, it takes at least 4 cycles really to see much change and usually many days on peritoneal dialysis to get electrolytes to normal. 

  • No vascular access is required, all one needs to do is put in a peritoneal dialysis catheter.

2. What are The Disadvantages of Peritoneal Dialysis?

The disadvantages of peritoneal dialysis include

  • It is quite labor-intensive unless you have a machine. So, in general, this is done manually unless you rely on gravity. 

  • You rely on gravity filling the abdominal cavity, gravity to drain the fluid down into the drain bag and factors that can affect that include if there is any blockage, fibrin leakage, and poor dialysis.  

  • Risk of catheter exit site infection, so not just peritonitis, but cellulitis.

  • There is a risk of hernias if you fill too much and injure the abdominal cavity, these patients may get a hernia. 

  • These patients also have respiratory failure, an increase in the abdominal cavity may decrease the lung volumes. 

  • Solutes are removed slowly, and therefore, peritoneal dialysis is not an ideal for use in the removal of ingested toxins life-threatening hyperkalemia or hyperammonemia. If dialysis were indicated for any of those clinical settings then hemodialysis would be the preferred method.