What is a double-volume exchange transfusion?

Hello, today's NICU Nugget is on exchange transfusions. Exchange transfusions are used less and less in the neonatal world just because of the advancement of other medications and techniques. However, sometimes it really is exactly what the baby needs so it's still important that you understand it and it also helps just a general understanding of the pathophysiology behind it. Most of the time we do exchange transfusions or specifically for unconjugated hyperbilirubinemia. Most of the time it's an immune-mediated hyperbilirubinemia and so what we're hoping to do is get all that free unconjugated or indirect bilirubin that's floating around the blood and get it out of the body. If that indirect bilirubin builds up then it could cross into the blood-brain barrier and cause conicterus. So what we're trying to do is make sure that that bilirubin level in the blood stays low enough that it doesn't cross into the blood-brain barrier. In immune hyperbilirubinemia, what we're also doing is removing some of those antibodies that are responsible for breaking down the red blood cells and so getting rid of those antibodies will also stop the whole process of releasing more bilirubin. In neonatal hemochromatosis, which is thought to be also an antibody-mediated disease, more recently double volume exchange transfusions are being used to try to get rid of those excess antibodies. So an exchange transfusion will get rid of the pigment that you're trying to get rid of but could also get rid of antibodies or anything else that's bad that's floating around the body that you want to get out. So why is it called an exchange transfusion? What we're doing is basically exchanging the baby's blood. So we're taking out the baby's blood volume and replacing it with effectively donor blood. We call it a double volume exchange because what we're normally doing is replacing two volumes of the baby's blood. So a baby normally has somewhere between 80 to 85 mls per kilo. So altogether we'd be removing 160 to 170 mls per kilo because it's double volume. Two times 80 or two times 85. Obviously we're not doing this in one go. We're taking out a bit then putting in a bit and the amount that we take out altogether will reach about 160 to 165 cc per kilo. So why do we do a double volume exchange transfusion? This is why. Obviously you can't take out all the baby's blood and then just put in new blood. So we have to take it out in small aliquots at a time anywhere between 5 and 15 mls basically. So if you take out for example 10 mls and then you replace that with 10 mls of the donor blood and then you take out another 10 mls, that second 10 mls is not going to be pure baby's blood. Some of it is going to be some of the donor blood that you just gave. Mathematically the washout of the infant's blood is basically a simple exponential function. So if you do a single volume exchange, so for 80 cc per kilo, you take out 10, put in 10 until you get to 80 cc per kilo, then you will end up washing out or removing about 63 percent of the baby's blood. If you do a double volume exchange, so you do it 10, 10, 10, 10, so it gets to 160 cc per kilo, then you'll end up washing out about 85 to 86 percent of the baby's blood. If you do a quadruple volume exchange, then you'll end up washing out about 98 percent of the baby's blood. Obviously that would be very time consuming and is associated with other risks. So basically you're pretty much getting your most bang for your buck at double volume exchanges because you're getting 85 to 86 percent washout. So what blood do we use for the procedure? Obviously we're taking out the whole blood, but what should we replace that blood with? If you remember or go back and look at the CBC lectures, blood is basically made up of four components. Red blood cells, white blood cells, platelets and then the plasma. So obviously we need to be replacing red blood cells and the basis for the donor blood is going to be red blood cells. If we're taking out 86 percent of the baby's blood and not giving any red blood cells back, then the baby would be extremely anemic and probably die. So definitely red blood cells. What about white blood cells? We generally do not want to transfuse white blood cells because those white blood cells will go inside the new body and attack that body. So that would be graft versus host disease from the donor white blood cells. What about platelets? If you remember what we said about platelets is that one, they are very redundant in that we have a lot of them, 250 to 300,000 of them, but really you're not going to have any bleeding issues unless that number falls below about 20,000. The second thing about platelets is that so the baby can continue to make platelets very quickly. So generally we don't add platelets to the donor blood that we're giving or we don't add WBCs either. So what about plasma? The plasma contains a lot of clotting factors and remember that if you're missing even half your clotting factors, you can end up with severe bleeding issues. So we definitely want to replace that plasma to some extent. In fact, the blood that we end up giving is generally red blood cells reconstituted with plasma or red blood cells reconstituted with FFP. So how is the procedure done? So like we said, you're pulling blood out and then returning blood. It's much easier if it's done with two operators, somebody's pulling and somebody's pushing, as well as if you do have both arterial as well as venous access. So it's great if you have an umbilical arterial line as well as an umbilical venous catheter, but you can also use a PAL, a peripheral arterial line to pull the blood out and you can use a peripheral IV to push the blood back in. You can also both pull and push from a double lumen UVC. So generally the aliquots that you use are about 5 mls per kilo. So if you have a 3 kilo baby then you can use aliquots up to about 15 mls and that's normally kind of the range that we use, somewhere between 10 to 15 mls. It's very important that when you're working with someone you're constantly communicating with them. It's very easy as you're doing this procedure to kind of just lose track of how much you've taken out and how much that person has put in. And the whole procedure should take between one to two hours if you're doing a double volume exchange transfusion. You don't want to go too fast and risk making mistakes and you don't want to go too slowly either. So what risks can occur? Probably the most obvious one is that you're giving a huge amount of donor blood to this baby. So you have to be very very careful that the blood is warmed exactly to the right temperature. If it's too cold then it would go inside the baby and cause hypothermia. If the blood is heated to too high a level then it can also cause hemolysis. So ideally the blood should be warmed to about 34 or 35 degrees. So what risk factors are you worried about? Obviously the biggest one is that you're worried about huge shifts in blood pressure or fluid volume causing hypo or hypertension. And then a lot of the other risk factors are related to the fact that you're giving donor blood. So donor blood has a lower pH. You're worried about acidosis developing in the baby. You're also worried about the chelating factors in the blood causing hypocalcemia. You're worried about the red blood cells hemolyzing and red blood cells or all cells have potassium within them. So if there's a lot of hemolysis then the potassium can be released and cause hyperkalemia which obviously can be very dangerous. If there is bleeding then logically you should be worried about not just the clotting factors that you're giving but also platelets. And you should probably just think about immediately giving a platelet transfusion. Because of all these electrolyte abnormalities when you're doing the double volume exchange transfusion you should probably be getting chemistries and gases about every half an hour just to make sure that the calcium and the potassium and the acidity aren't completely out of whack. There is also an increased risk of neck with double volume exchange transfusions. Obviously this is a much higher risk if the baby is preemie. Even so, even in full-term babies we generally make these babies NPO and rest their gut just to hopefully lower the risk of them developing neck. One last thing to remember is that you have to get consent for the blood as well as consent for the procedure itself. Obviously it has some severe risk factors but like everything in medicine it's all a balance between benefit and risk. So you really only want to do this procedure if it's really going to help survival or really help developmental outcomes. I hope you learned something today. Please remember to like and subscribe and let us know what else you'd like to hear about. Thank you.