Sunday, October 20, 2013

Strategies to Avoid Fainting While Donating Blood

High Iron

For me at least, an unfortunate consequence of being Paleo is that my iron levels increased.  I went Paleo in late December 2010, about a year after that (January 2012) I got a blood test back and my ferritin was 166 µg/L (µg/L=ng/ml.  No conversion necessary!), then one year later (January 2013) the blood test showed my ferritin went up to 220 µg/L and the other markers (serum iron, transferrin and saturation) also increased. 

Iron levels are regulated to some extent, though not quite as well as sodium, potassium or calcium.  As for why I have high iron, perhaps I have a polymorphism/etc (something genetic) that promotes iron storage or accumulation, or perhaps it’s simply due to being a male who eats a fairly nutrient dense diet and a non-starvation level of calories and this is another part of the mismatch where HGs would have bled and had other blood loses more often than we do (not that I buy into the whole ‘nasty, brutish, and short’ thing). 

So being familiar with the idea that having high ferritin levels isn’t good (see Chris Kresser’s talk below) I started donating blood (I know totally selfish, but if more people with high ferritin donated blood out of self-interest the blood banks would be fuller, there would be less chronic disease and medical expenses would be lower).  (Anthony Colpo talks about his experience with blood donation and ferritin here) 


The first time I donated was in July.  I was quite anxious about fainting and there were two occasions when I did feel like I was trending towards fainting, but I ended up not fainting and feeling fine shortly afterwards, it was only during those two periods. 

I stumbled across some papers about fainting and blood donors while doing research for a somewhat unrelated assignment*, which allowed me to better prepare myself for next blood donation, which was earlier this month. 

Some Notes on Fainting from Blood Donation: 

The frequency of fainting among blood donors is actually really low (0.1-0.3%) [1] (0.17%) [2].  Those 0.1-0.3% probably didn’t adequately prepare for the blood donation and/or have poorer health than you.  The statistics are strongly on your side 

Most fainting occurred around when the needle was taken out or shortly afterwards when people stand up [1].  Not sure why for the needle (maybe fear of needles?), but standing up is more obvious.  Our upright posture and big brains are quite a challenge for the cardiovascular system**.  When you stand there is a transient pooling of blood in the legs (of about 300-800mL) before compensatory responses kick in, then combine that with a loss of ~500mL of blood (10%) from the donation.  No rush, stand up when you’re ready 

Strategies to Avoid Feeling Dizzy or Fainting: 

Increase water and salt.  The Red Cross/Google searches/Yahoo Answers/etc really only tell you to eat and drink lots of water prior to donation.  In addition to a loss of ~320ml of water (because blood is mostly water) you also lose 1,200mg of sodium (to put this in perspective, the RDI is <2,300mg and the average person eats 3,000-4,000).  Not only would you want to offset that loss, but increasing sodium prior to blood donation should be helpful as it enhances water retention and increases plasma volume expansion [1] 

Reduce stress and focus on regular breathing.  Being anxious is counter-productive.  Most people who faint have an aversion to needles and/or blood and often tend to be on the more hypochondriac end of the spectrum.  Stress increases the respiratory rate which lowers CO2 levels.  Lower CO2 levels in the blood causes vasoconstriction of the blood vessels to the brain and vasodilation of the blood vessels to the muscles, which decreases blood flow to the brain while lowering blood pressure (the effect of stress on CO2 and CO2 on blood flow makes sense when you consider the evolutionary context of stress).  In addition, lower CO2 increases alkalinity, which reduces oxygen uptake by tissues (the Bohr effect).  Before I knew this, I found that focussing on my breathing increased my breathing rate.  If anything, you should decrease your breathing rate (without deep breaths or holding your breath) to increase CO2 levels.  Increasing having a meal with carbohydrate prior to blood donation could be helpful by increasing CO2 production. 

Tense the muscles of your lower-body.  This is to activate the muscle pumps to return blood from those areas back to the heart, to increase blood flow to the brain 

Sit/lie in as much of a horizontal position as you can (lying down is ideal).  This is to reduce hydrostatic pressure to make it easier for blood to get to the brain 

This study has a list of recommendations for donation centres but you (the donor) can apply some of them as well (just read the conclusion section) 

After implementing these strategies, the second time went really smoothly, of course it could have just been because I was less anxious the second time as it was no longer a new experience, but I like to think that the noral of the story is that: PubMed > Yahoo Answers 

* The assignment was to find out why someone fainted while doing a clean and jerk.  Just very briefly, the three main reasons were that the lifter hyperventilated prior to the lift (not excessively, more of a psych up), remained in a squatting position for a while and performed the valsalva manoeuvre.  The valsalva manoeuvre is unavoidable, but excessive breathing and prolonged squatting are not.  If you’re concerned about fainting while weightlifting I would suggest not doing the latter two.

** For more on the cardiovascular challenges of our vertical posture look at the tilt table test and read the comments 

*** Blood pressure medications may increase the risk of dizziness or fainting from blood donation.  Discuss with your doctor

1 comment:

  1. hmmm i didnt know salt and water were needed prior to donation. thank you for the much needed information. i donated thursday and after one round of donation i was feeling funny. only 250ml was i able to give. they say there are 4 rounds to accumulate 880ml. i plan on goinf back this next week and the information i read will be used

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