Once again, this is quite wrong. While it is true that liquids will boil at much lower temperatures with less pressure (there is less pressure preventing the liquid from turning into a gas), it wouldn’t happen to your blood. Why? Because your blood is in a closed system and the effect of zero pressure wouldn’t affect it immediately. Of course, liquids exposed to the environment would boil right away (saliva, eyes, etc). Keep in mind this doesn’t mean they would be hot. They are simply turning into a gas due to the lower pressure.