Suppose I’ve just given blood a couple
of hours ago, so that the amount of fluid
in my bloodstream is about the same as before
I donated, but I’ve got about 20% fewer
red blood cells than before.
I am involved in a severe trauma. How much
quicker will I bleed to death now than I
would have if I hadn’t given blood?
I’m not trying to start a moral argument
here, I’m just curious.
My WAG would be 20% faster… 
“Through twilight, darkness and moonrise
My scarlet tears will run
As stolen blood and whispered love
Of fantasies undone”
Well, yeah, my WAG would be EITHER
20% faster, or about the same.
Does anybody know?
Well, yeah, my WAG would be EITHER
20% faster, OR about the same, it
doesn’t really make a difference.
Does anybody know?
It’s becoming way too common on this board to ask questions that can easily be answered with a simple experiment. All that’s really required here is two volunteers, a sharp knife and a stopwatch. Let us know what you find out.
“I’ll tell him but I don’t think he’ll be very keen. He’s already got one, you see!”
I have verified by independent experiment that an animal that has given blood will in fact die of bloodloss faster than an animal that has not.
On a completely different topic, how do you tell a child that her puppies are dead?
It may depend on what you mean by “a few hours ago”.
If there’s been sufficient time since the initial blood-letting (say 6 hours or more) you will have probably restored your circulating blood volume although not your red blood cell level. This will have occurred as a result of salt and water leaving the tissues and entering the circulation to replace the lost blood.
Once your blood volume has been restored to normal levels, you’re essentially back to square one in terms of being able to tolerate further blood loss. In other words, in the vast majority of cases, people who “bleed to death” have died from lack of circulating blood volume and not due to lack of the red blood cells (and the hemoglobin therein). Phrased yet another way, the key thing is that there’s something to circulate, even if it is just salt and water (within reason). As long as some fluid circulates, red blood cells will be mobilized in sufficient quantity to deliver oxygen to the tissues. Again, within reason. Obviously, you’ll die if there are absolutely no red cells left.
As proof, (well sort of proof), people with massive blood loss can be stabilized simply by giving them salt water solutions. The need for urgent red blood cell transfusion is vastly overestimated. Look at Jehovah’s Witnesses for example. They have survived, without transfusion, with red blood cell and hemoglobin concentrations of less than 10% of normal! (If normal hemoglobin is 15, they have lived with 1.5).
Finally, a period of previous blood-letting may stimulate various hormones to actually better prepare your body for further stress such as more blood loss.
The hypothetical scenario posed in the OP was that he/she had given blood. Assuming this was a standard donation, his/her “blood loss” would be 500ml: one standard unit of blood.
A 70kg adult has about 5 litres of total blood volume, based on the formula:
volume=70ml per kg (body weight)adults
volume=80ml per kg children
volume=90ml per kg infants and neonates
Hence the hypothetical blood loss would be about 10% of total volume, depending on body weight.
Hypovolaemic shock (shock caused by loss of circulating volume) is graded into four categories of increasing severity: classes I, II, III, IV.
Class I= 0 to 15% loss
Class II= 15 to 30% loss
class III= 30 to 40% loss
class IV= 40% or greater loss
As you have no doubt perceived from your visits to the blood bank to donate blood, there are vitually no changes in normal body signs when you give blood - a deliberately induced class I haemorrhage. What do you get to compenstae for the fluid loss? A nice cup of coffee or tea, and a little sit down just to make sure you drink it. As you have observed correctly, you body will readily compensate fluid loss within two hours by shifting fluid from body tissues to restore circulating volume, and by reabsorbing water that would otherwise have been passed in urine.
Blood loss must be class III or IV to become life threatening, and profound signs and symptoms don’t become evident until the transition from class II to class III.
Knock softly but firmly, 'cause I like soft firm knockers…
Thank you.