Of course this sounds obvious, but what I am referring to here is something very specific. All nurses and docs see examples of a very peculiar phenomenon every day, especially in the ER.
What I am talking about is this: if any given human organism has time to slowly adapt to a deficit, it will do so – even if that deficit is deadly. For example, in the ER we routinely transfuse if the hemoglobin is less than 7. So 7 is low – low enough to emergently transfuse someone with blood. Low enough to become lethargic and short of breath with activity. Low enough to be considered a true emergency.
So what are we make of someone with a hgb of 1.5? How is this possible? What if I said this person was able to engage in a coherent conversation?
The answer to all this is that, if you are bleeding slowly enough (think GI), over a long enough period of time, your body will just as slowly adapt.
If, however, you sustained a trauma and bled out quickly (resulting in the same hgb of 1.5), now you’re dead.
Like I said – the human body is an amazing thing.