Peritoneal Dialysis by Dr. Sharon Su. Introduction. Hello, my name is Dr. Sharon Su. I’m a Pediatric Nephrologist. Today I’m going to talk to you about peritoneal dialysis. First off, we need to define what peritoneal dialysis is. Number one is the use of the peritoneal membrane to do three things. One is to remove the fluid. And we call that “ultrafiltration.” Number two is to restore the balance of blood chemistries. And number three is to filter waste products.
And this requires a mixture of fluid and electrolytes to to perform this dialysis. And this type of mixture of fluid and electrolytes,we will be calling “peritoneal dialysis fluid.” Principles Behind Peritoneal Dialysis. Few more concepts before we go into the details of peritoneal dialysis. Number one is the idea of osmosis. Osmosis is the movement of water across a membrane. In this case, it would be the peritoneal membrane,from areas of low solute concentration to areas of high solute concentration. So if you can see this diagram, you can see that the water molecules are moving towards the area where there is lot more sugar molecules, because there is a higher solute concentration. The second concept for peritoneal dialysis something called “diffusion.”
Diffusion is the movement of molecules across,again, a membrane, and again, in this case, the peritoneal membrane, from 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. If you will see from the diagram, you can notice that the molecules that have higher concentration will move over to the areas where there’s lower concentration. Another concept is called “ultrafiltration.” And this is a very important concept. This is how much water you want to remove. And ultrafiltration, is calculated by volume removed minus fill volume.
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. And so you’ve actually removed a net negativeof 50 mLs. It’s very 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 netremoval of fluid. Some factors affecting ultrafiltration– dextrose is what we use to pull the water out because of the concept of osmosis. So higher dextrose concentration will allowfor more water removal. If you increase the dwell time, the amountof time the 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 you put into the peritoneal cavity, that will also allow for larger water removal or increased ultrafiltration. If you want to decrease ultrafiltration, soif you’re removing too much fluid too quickly, and you worry about hemodynamic instability,then you can decrease the dextrose concentration, decrease the fill time, and decrease the dwell time. Dialysis Set-up.
For fill volume, it’s 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 start usually with 5 mLs per kilo offill volume, and can go up slowly, depending on the size of the patient. The usual final goal of fill volume is 20to 45 milliliters per kilogram. Again, you have to be very careful in howquickly you fill and how large the volume is, as the more volume put into the peritoneal cavity, the higher chance of leakage around the catheter site, which leads to risk ofinfection, as well as poor efficacy of peritoneal dialysis. Other things to consider when you’re determining the fill volume is, not only the size of the child, but does the child have any pulmonary diseases?
If you fill too much, the volume in the peritoneal cavity, or the abdomen, will push up on the diaphragm, and patients may have difficultybreathing. Point of clarification, be sure to check withyour hospital’s policy on the maximum goal fill volume, as the level may vary among institutions. The next concept is called “fill time.” This is the time you allow the peritoneal dialysis fluid to fill into the peritoneal cavity. Usually the time is 5 to 10 minutes. Third concept is called “dwell time.” This is the time you leave the peritoneal dialysis fluid into the peritoneal cavity. Usually this is around 30 to 45 minutes. Sometimes it’s easier to combine the two together,of fill time and dwell time, especially if you have no machine available to pump thefluid in. And you can set the whole fill time to 45to 50 minutes. It is a larger patient, then a good dwelltime would be 2 hours. The next is drain time. The drain time is the amount of time to removedialysis 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 again, the cycle includes the fill time,plus the dwell time, plus the drain time, as we call, “exchanges.” What about factors to remove molecules, because peritoneal dialysis is not only water removal, but also molecule removal. The ways to remove molecules is dependent,again, on diffusion. So molecules that are very small will movemuch quicker than molecules that are very large. So size of the molecule will affect the removal rate or the efficacy of that molecule. An example of a small molecule would be creatinine. An example of a large molecule would be albumin. So this chart shows you that each molecule has a time point to allow for the greatest amount of movement. Smaller molecules, again, like urea, takes less time to remove. And you can see that after about 2 to 4 hours,you’re not going to get much more removal of urea. Larger molecules, again, like albumin, will take longer to remove. So you need to dwell longer if you want to remove albumin.
Fortunately, in general, peritoneal dialysis is used when patients have renal failure, which means they have an accumulation of urea and creatinine. And those are the ones that need to be removed. And 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 lower concentration of, for example,sodium, into the dialysis fluid, and let’s say the patient’s sodium level is 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 alsoallow for more removal of molecules.
If you increase the dwell time, you allowfor more removal of molecules. Finally, if you increase the drain time, you will hopefully drain more fluid. And therefore, you will increase removal of molecules. Peritoneal Dialysis Fluid. The fluid is made up of water; dextrose, whichis the osmotic agent; buffers, such as acetate, lactate, bicarbonate; electrolytes, sodium,potassium, calcium, magnesium chloride; and in some cases, medication. 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 you do not have availability forthe standardized bags, then one can make dialysate bags of their own. I’m going to give you two examples of dialysate bags that can be easily made.
Both of these will give you one-liter volume. Number one includes 680 milliliters of normal saline, plus 320 milliliters of D5% dextrose, and 5 milliliters of D50 dextrose. A second formula, you 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 a one-literdialysis bag. Point of clarification. These are example of dialysate recipes. Be sure to check with your institution’s policyon how to create a bag of dialysate for your hospital. Peritoneal Dialysis in Practice. So let’s talk about the peritoneal dialysis protocol. First thing is to determine the fill volume. If the catheter was placed immediately and peritoneal dialysis needs to be performed, then I recommend that small fill volumes be started to avoid leakage. The next is 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’re going to have a one hour cycle,60 minutes, then a good dwell time would be 40 to 45 minutes. If you’re going to do a two-hour cycle, thena good dwell time is 100 to 105 minutes. If you’re going to do a three hour cycle,then a good time is 160 to 165 minutes. Next is to determine the drain time.
In a one hour cycle, usually the drain time is about 10 minutes. Number two is then to record the ultrafiltrate. And then we’ll check electrolytes. This is especially important in the initiation of peritoneal dialysis. I recommend checking within two to four hours. After that, once it’s routine, one can checkonce a day or twice a day, depending on the resources available. Number three is to assess the ultrafiltrate,the net removal of water. So once you start peritoneal dialysis, periodicallyyou need to re-assess.
Do you want to increase ultrafiltrate or doyou want to decrease? Number four is to weigh the patient daily. This is very important as this is how we determine patient’s fluid status, as well as the ultrafiltrate. Number five is to check blood pressures frequently,especially in initiation of peritoneal dialysis. If you have increased or very efficacious ultrafiltration, there’s a risk of causing hypotension. Number six is if you have to temporarily discontinue peritoneal dialysis, it’s very important to keep the catheter site clean. So the steps to do this is, one, to completely drain the peritoneal dialysis fluid. Then to fill with new peritoneal dialysis fluid, but only to 50% of your fill volume. So you don’t want to fill completely, but you want to leave a little bit of fluid into the peritoneal cavity. This will allow the catheter to flow freely in the peritoneal cavity and prevent it from touching other organs, which may cause block age and complications of peritoneal dialysis in the future. Please note the amount of peritoneal dialysis fluid inserted during temporary discontinuation may vary among institutions. What are some of the advantages and disadvantages of peritoneal dialysis? Well, the advantages include, one, this isa very gentle way of removing fluid as well as molecules. So for patients who have hemodynamic instability,peritoneal dialysis is very safe. Slow correction of metabolic imbalances. So the risk of dropping a serum sodium too low, less likely with peritoneal dialysis. In general, it takes at least four cycles really to see much change. And usually many days on peritoneal dialysisto get the electrolytes to normal. And finally, no vascular access is required.
All one needs to do is put in a peritoneal dialysis catheter. What about the the disadvantages? It is quite labor intensive, unless you have a machine. So in general, this is done manually, unlessyou rely on gravity. You rely on gravity filling the abdominal cavity, gravity to drain the fluid out into the drain bag. And factors that can affect that include ifthere is any blockage, fibrin leakage, and poor dialysis. Risk of catheter exit site infection. So not just peritonitis, but cellulitis. And there’s a risk of hernias, if you filltoo much and injure abdominal cavity, these patients may get hernias. These patients also have respiratory failure.
Increasing the abdominal cavity may decrease the lung volumes. Lastly, solutes are removed slowly, and therefore, peritoneal dialysis is not 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. Absolute contraindications include omphalocele, gastroschisis, bladder exstrophy, diaphragmatic hernia. A relative contraindication may be recent abdominal surgery. And the reason being, again, if you put catheter in when a patient just came back from abdominal surgery, there’s a high riskof leakage, as well as an infection. This concludes the video on peritoneal dialysis. Thank you. Please help us improve the content by providing us with some feedback.