Question

If a wound overwhelms the clotting mechanism and leads to serious hemorrhage and drop in blood pressure, what compensations does the body have to defend cardiac output?

Answer 1

There are a few things that can happen when a serious amount of blood is lost: these include tachycardia, or increase in heart rate, peripheral vasoconstriction which is narowing of blood vessels leading to cool skin which looks pale. You could start here for more details:

http://en.wikipedia.org/wiki/Hemorrhage