Blood, sweat, but no tears
March 18, 2010 12:08 PM   Subscribe

Why did I sweat so profusely when I donated blood?

I donated blood for the first time on Tuesday and started sweating profusely. What's the explanation for this? The nurses didn't seem particularly surprised by this, but didn't really explain why it would happen.
posted by dfriedman to Health & Fitness (14 answers total) 1 user marked this as a favorite
Is it possible you were a tad apprehensive about having a big bag o' blood drained from your body? That'd do it.
posted by Sys Rq at 12:11 PM on March 18, 2010

It's possible, but my pulse and blood pressure were on the low range of normal (60 bpm, and 60/100, respectively), so I'm not sure apprehension came into play...
posted by dfriedman at 12:13 PM on March 18, 2010

I can't offer a why, in physical terms, but the third time I donated blood, whilst recuperating at the tea 'n' biscuits table afterwards, all of sudden out of nowhere I started to throw a whitey. The early warning signs (for me at least) were that I was feeling intense prickly heat and sweating, and the nurses spotted that, asked me "Are you feeling hot?", and as I answered in the affirmative, they responded by getting me to a couch where I lay down just in time before I fainted. They seemed to pick up on the sweating as an outward manifestation of a problematic rise in temperature that signalled that I was about to faint, and responded accordingly. Nothing was wrong of course. Or nothing at least that a bit of sit, a ginger nut, and some weak lemon drink didn't cure.
posted by hydatius at 12:24 PM on March 18, 2010

You were probably on the outer verge of hypovolemic shock:

Other features of hypovolaemic shock are similar to those seen in cardiogenic shock and include cool peripheries, decreased urine output and sweating

The article I linked calls these things 'sympathetic compensatory responses', which seems reasonable, but it's a little paradoxical that losing blood volume would provoke a response that involved losing even more fluid.

Perhaps it works by making your skin cold, which produces vasoconstriction, which makes the most of reduced blood volume by reducing the volume it has to fill.
posted by jamjam at 12:50 PM on March 18, 2010

Sweating is one of the symptoms of a vasovagal episode.
posted by ottereroticist at 12:53 PM on March 18, 2010

You were probably coming close to experiencing vasovagal syncope--aka fainting. It's not unusual, it doesn't necessarily happen to the same person every time they give blood (or do something similar), and it's not like fainting on TV or in cartoons where a person just seems to fall asleep immediately on their feet. It also doesn't necessarily happen immediately, it can happen several minutes after a trigger such as being poked in the arm with a needle.

Before a person faints like this they will often go pale (or even green), start visibly sweating, their vision will turn blotchy, their hearing will go fuzzy (everything will sound distant), they feel hot, nauseated...and some people will go all the way and start twitching as they lose (and then regain consciousness). Not everyone experiences all these symptoms before losing consciousness, and only a few actually do lose consciousness. Most people have a few symptoms (feeling hot, nauseated, and lightheaded), feel ill for a few minutes, and gradually come back to normal.

It seems to happen (in my experience) more with people who have low blood pressure, low blood-sugar (so don't give blood on an empty stomach), are anemic or exceptionally nervous--with an empty stomach being overwhelmingly the biggest predictor of near or complete fainting.
posted by K.P. at 12:55 PM on March 18, 2010 [3 favorites]

In my experience, it's completely a mental thing.

The first two times I donated blood, I got on the table and halfway through I got real pale, I started to sweat, my stomach hurt, I felt dizzy and was super lightheaded. They gave me a bunch of juice and put me on a special cot to wait until I felt better. I attributed this to the loss of blood, but the next time I went changed my mind. That time, I went in but never donated. They did the finger-prick test for iron and my count was way too low. Five minutes later I'm chatting up a friend and all the same feelings come rushing back- so strongly I thought I was going to pass out. I ended up having to sit down with my head on a table until it went away. The fact that they never even took blood and I was still feeling horrible made me realize that it was all a matter of nerves.
My most recent experience was much better. Unlike previous trips, I went with a few friends and the nurse drawing blood was really talkative and funny. I was talking the whole time and not really focusing on what was going on. Before I knew it I was done, and not once that day did I feel like passing out. I'm hoping the next time I go in it'll be the same.

But YMMV. Hope this helps!
posted by pyrom at 12:58 PM on March 18, 2010

I'm too light to donate blood, but once, I drank a ton of water to push me just over the limit and did it anyway. Same thing happened - I sweated profusely, skin felt hot, looked like a ghost, felt weak, ears and eyes started to fail me - and I woke up on the floor. It happens - not due to fear, just because of low blood pressure. Mine is naturally 95/60, and after losing so much blood (relative to my size) my body just didn't respond well.
posted by Cygnet at 12:59 PM on March 18, 2010

Oh, and it's no big deal and easily cured by apple juice and cookies and lying down for a few. Just don't try to move too fast after donating until you're sure you're OK - I glad I fainted immediately after getting up, as opposed to in a hallway someplace. I felt fine during the whole blood draw, too, so there was no indication that it was coming. Just take it easy for a bit...
posted by Cygnet at 1:01 PM on March 18, 2010

I think K.P. nailed it, thanks!

Very interesting. But for the nausea I had all those symptoms.
posted by dfriedman at 1:16 PM on March 18, 2010

Not nerves. I gave blood consistently for many years, am generally a big healthy guy, and never had a problem. Until ....

It had been a very hectic day, with lots of running around here and there in the heat, and probably the only thing I drank all day was a big cup of coffee. My blood pressure was noted as being on the low side before they started, but it didn't seem like a big deal so away we went.

I was almost through when I started sweating, felt hot/cold, started seeing bright sports, etc.. I managed to croak something, then passed out. Apparently I was only out for 30 seconds or so, but (and this was the worst of it) when I started to come to I had no idea where I was or what I was doing. It was, frankly, fucking scary. It look some time before I could even get up, and (maybe because I still wasn't thinking straight) I was anxious to get up and get out of there, so I sorta faked it and got the staff to let me go. I walked outside and immediately puked. Luckily my wife was around to pick me up and take me home.

In all, not a good experience. But it got even worse when I got a call from the blood bank the next day asking how I was, and proceeding to ask that I never give blood again. I've been black balled.

Point is: LISTEN to the good people when they tell you to eat/drink good stuff before giving blood. There's a certain macho attraction to thinking that you're tough enough to loose a pint or two without consequence but trust me -- there are limits.
posted by lex mercatoria at 1:49 PM on March 18, 2010 [1 favorite]

If it turns out that this is a regular occurrence for you (feeling faint after giving blood) you might consider donating platelets instead. Despite the fact that can take ten times longer, it can be easier on your system because so much of your blood volume is returned to your body.
posted by SuperSquirrel at 2:04 PM on March 18, 2010

If your blood donation center offers it, ask them for the anesthetic before they put in the donation needle. I came close to fainting every time I donated blood* until I learned about this. The needle they use to inject the anesthetic is much, much smaller gauge than the donation needle, and for me it seems to keep the vasovagal episodes safely at bay.

* The second time I donated blood was at a blood drive at work, which turned out to be staffed by the people from the blood bank I'd donated at the first time. When I walked through the door, one of the nurses saw me and called out, "I know you — it's the dizzy redhead!"
posted by Lexica at 12:03 PM on March 20, 2010

Well everyone has pretty much nailed the reasons, but as a blood bank employee I thought I'd offer this advice (of course IANAD). Make sure you've eaten a good meal a few hours before donating, and drink a lot of water. Tell the phlebotomist that you tend to have a mild reaction and ask for some ice packs. They might pre-emptively elevate your legs too.

Good luck!
posted by radioamy at 9:38 AM on March 21, 2010

« Older Hot town, summer in the city... back of my brain...   |   what to do with our extra money Newer »
This thread is closed to new comments.