How do you know when a blood bag is full?

We want to fill up our blood bag as close to 450 mls as possible. If we underfill it, then we have extra anticoagulant compared to the blood that we have in the bag. That anticoagulant, we don't want it going into our casualty and creating more of a problem. So it's going to hurt their coagulation, and they're already in hemorrhagic shock. It's also going to bind calcium, which is the mechanism that it works by. So it's going to drop their calcium a little lower. Overfilling the bag is something that you don't want to do because then you don't have enough coagulant circulating with the blood, and you could get blood clots in that bag of blood.

So we want to get it just right. We want to get it as close as possible. The real gold standard is to use a scale, and that's what you'll see them doing at the blood bank, but you're not going to carry a scale in your bag. You're not going to have it out on target. So we need a better field expedient way of doing this.

So the first thing that I'll do is I'll take my beaded cable tie. As you can see here, it's pre-marked at the six-and-a-half-inch mark. Place it around my blood bag and lock it off right at the mark. I'm then going to place that on the scale just for demonstration purposes. Remember that a bag of CPD, a 450 ml bag, plus the CPD weighs a little over 100 grams.

So when it's full, it should weigh 585 grams. If you tear out the scale, then it's going to weigh about 475 grams. I've got my beaded cable tie secured at the six-and-a-half-inch mark. Next thing I'm going to do is I'll remove the safety cap. I'm going to simulate drawing a unit of blood off a donor by placing it in this bag of saline, and then we're going to start watching it fill.

As we get past 500, you see that the bag is really starting to expand, and meet some resistance. And right at 585, it really just won't go anymore. You might be able to get it to 600, depending on the donor's diastolic blood pressure. We're going to stop right there and take a look. So I know my weight is right. Nice tension on the bag.

After that, I will remove the clip.

And then you can get a good feel of what a 450 ml bag of blood feels like. So you can see it's nice and full. We've got a little bit of dimpling in here, but we don't have this big, overextended, super firm bag. Also, it's not really floppy and not full of enough blood. And we're right at 565 grams. So we got pretty darn close just by using a simple little beaded cable tie.

And now you know how to properly fill a blood bag.