It seems to me that you hit over the spine. In fact I' m absolutely 100% sure you hit the backstrap. It is not fatal and often bleeds enough for a blood trail. It will leave little or no blood on the shaft and often will not make a complete pass through for whatever resons. There is bone in the backstrap which sometimes causes it to make a loud smack sound. Meat and grease will be on the fletching and shaft. The deer should survive but there is always chance of infection.
Don' t worry, it happenes.

As for the dead spot, c903 and Mez are right. Anyone who knows anything about anatomy knows that the body cavity is completely air tight unless punctured. As stated, it needs to be air tight for resperation to occur. Although it can also occur without being air tight. I did not know each lung was inside it' s own membrane until I read this. That explains one lung hits. I do autopsies on each animal I kill to determine the cause of death. Everyone should do it. There is a small amount of fluid in the chest cavity but definately no air. No dead spot between the lungs and spine. Therefore that definition of the dead spot is false.

That' s not to say there is no dead spot. There are low percentage areas of the lungs where you could hit with an arrow and the animal might survive allthough it will usually be fatal. Combine that with a dull broadhead and the chances of an animal surviving marginal hit to the lungs in much higher.

Dull broadheads (especially 2-blades) can be slipped between organs. Even over the lungs and under the spine while cause hardly any damage other than scratches and shallow cuts. That could also explain the dead spot.

There can even be fluke occurences where an animal survives a double lung hit for whatever reasons. Somehow it just toughed it out.

Things like that sometimes happen but there is no dead spot.
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Buckshot, when you exhale, because of the vaccum, your chest shrinks. Try it out. Take a deep breath and notice how your rib cage expands. What kind of blood was it? If you really hit the rib cage and lungs, then your arrow should have easily passes all the way through unless your broadheads were extremely dull. If you hit lungs, there would have been bubbles in the blood. No, you probably hit in front of the lungs and above the spine. Sometimes they aren' t where you expect. She must have had her legs forward or something. But there is no part of the chest that you can hit without hitting vitals. Unless a dull broadhead somehow slipped between the organs without doing much damage but at most treestand angles, that is unlikely.

PAHUNTER21, ??in front of the intestines is the stomach. In front and above the stomach is the liver. It fron' t the liver and between the lungs is a membrane called the diaphram which separates the chest and abdomental cavities. Hair tells you that you hit it but to have no blood? You probably hit meat and anothing else.