Fellows,
I’m reading about donating blood, and they said that in large volume plasma donation, a replacement of saline is added to your blood stream to account for the large volume taken. I’m just wondering how it’s okay to just replace blood with Saline
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It’s to keep your blood pressure at a healthy level, not to replace the plasma you’ve donated. When you lose blood volume there’s just less water in the pipes so to speak. At a certain point, you lose so much blood that when your heart pumps, your blood doesn’t circulate enough. You may still have enough oxygen and other nutrients in your blood to get by, but there’s just not a high enough water pressure in the pipes to get it where it needs to go. Saline just adds some neutral bulk to your blood to keep things moving while your body replenishes the plasma you donated.
Your blood already contains a good amount of water so in order to maintain proper blood pressure levels, a saline solution can be added to your blood to maintain its volume. Kind of like adding water to a concentrated drink and your blood cells are still able to carry oxygen throughout your body even if your blood has been diluted this way.
You dillute your blood with salt water. It doesnt do the same, you could not replace all blood that way.
Saline just replaces water and salt. When a person is dehydrated (from vomiting a lot for example), they’re mostly missing water and salt so it’s ok to use that. When if a person has enough red blood cells and other blood components, you need enough water/salt to keep up the pressure in the system so all those cells can circulate.
If you give too much saline, it will dilute the red blood cells and start to cause problems. This is especially true if somebody is already anemic or is losing a lot of blood. Giving lots of saline when somebody is losing blood also dilutes clotting factors, which can make the bleeding worse. For those reasons, blood products are preferred for people who are having major bleeding.
Saline is just slightly salty water. They inject that into donors to prevent a drop in blood pressure. The stuff that’s in the donor’s plasma that the recipient needs (platelets, for example) will be replenished by the donor’s body on its own.
https://en.wikipedia.org/wiki/Saline_(medicine)
https://www.utmb.edu/pedi_ed/corev2/fluids/Fluids6.html
As opposed to water?
Your body is made of cells that are mostly water with stuff in them. The cell membrane is semipermeable, so water can move back and forth as needed: https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/v/osmosis Replacing your blood with just water doesn’t have enough stuff, so water will rush into your cells. This is not good.
Oh this is a fun question! It can get really complicated. The basic answer to your question is that saline has about the same concentration of stuff dissolved in it as plasma (keep in mind it is ABOUT, not the same!), which is the fluid your blood cells are floating around in. When you donate plasma, the fluid is removed and the blood cells are returned to you. So, if you replace the plasma fluid with something that has about the same concentration of things dissolved in it, then that should keep the volume of your blood high enough until your body can make more plasma.
So, the saline does not replace your blood, but since it is about the same concentration of dissolved things (solute) in it as your regular plasma, it works well enough to increase your blood volume and get the blood cells where they need to go. Other types of fluid won’t stay in your blood stream and will distribute into your cells too, like straight water (which we give as dextrose in water to prevent your cells from exploding from fluid rushing into them when it first enters your blood stream), so it doesn’t work for keeping your blood volume up. You could also get blood back (which will for sure stay in your blood stream since the blood cells are trapped by the vessel walls), but that’s expensive and not as easy to do as saline.
Did you donate blood or did you donate plasma? If you donated blood, the saline is more or less to keep you at the right fluid level in your body (the saline solution matches the salinity of blood). It does not replace the loss of blood cells, so you will feel anemic and it will take your body several weeks to replace the lost blood cells.
If you donated just plasma, the blood cells are given back to you. Again the saline replaces the lost fluid, but since you did not lose blood cells you won’t be anemic. With such an exchange in plasma donation, you are losing antibodies and hemoglobin for the most part, so you have lost protein that you need to replace. This is done much more quickly than regenerating blood cells
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