Steve Casomere asked:
Do we bleed blue blood out of our veins? Presumably if you bleed blood it’s the oxygen that makes it turn red. If we bleed in a vacuum would it bleed blue?
The answer is definitely no. In hospital they use things called vacutainers which is a vacuum in a tube. You put a needle into a patient’s vein, put the tube onto the needle and this exposes the inside of the vein to the vacuum and draws the blood into the tube. Momentarily the blood is exposed to a vacuum and the blood comes out very red. There’s still too much oxygen in venous blood to make sure it stays a red colour.
So why do veins look blue?
This is because when you have a bit of the tissue which doesn’t have enough bloodflow going through it tissue will remove more oxygen from the blood. It does mean haemoglobin can get to be a blue colour. Normally that doesn’t happen but if you have an area of the body that doesn’t have enough bloodflow through it then the tissue gets oxygen hungry and removes enough oxygen to make it go blue. Veins look blue as an optical illusion. They’re not really blue and if you cut through the skin you’ll see they’re a whitish pink colour.
Steve Kazemir asked the Naked Scientists: I was talking with my children the other day, and we were noticing our blood vessels under our skin, and how many of then are blue in colour. I explained that blood changes colour when it has been oxygenated. So even if you cut yourself and blood came out of a “blue vein”, the blood would hit the oxygen in the air and turn more bright red. So, if we were to put our arm into a sealed container, with no oxygen in it (presumably with some other non reacting gas…nitrogen perhaps?), and then bled, would we bleed blue blood? Thanks for the fantastic show! Steve What do you think? Steve Kazemir, Fri, 2nd May 2008
There is usually too much oxygen in venous blood for it to turn blue in-situ. It's actually an optical illusion that veins are blue. And sticking a needle into one results in reddish blood emerging, so it's definitely not the blood that's blue.
I believe it's quite a common experience to bleed into a vacuum. A lot of blood samples are taken into evacuated tubes. They still look reddish but less so than if you just cut a finger and it bleeds into air. I will ask one of my colleagues who specialises in sticking needles in people. Bored chemist, Sat, 3rd May 2008
This thread here
How good of a vacuum do hospitals use because the oxidation reaction of Iron according to thermodynamics Ellingham diagrams you need a really good vacuum greater than 10^-11Pa to prevent oxidation of blood. Scientifically speaking 10^-8Pa is used for SEM and TEM microscopy measurements. Also lower vacuum pressures are not possible because you literally pump hydrogen through the vacuum chamber walls. The vials in hospitals are no where near this order of magnitude and are probably just to induce blood flow. See the chart Science doesn't lie. At room temperature 25*C it is just not thermodynamic-ally favorable to occur. Well Science, Sun, 13th Sep 2015