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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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.
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