Is it okay for a patient to be sedated by gas for a blood draw?

Yes: I have never done it. But if a handicaped person needs it it be still for blood tests that will make a real difference in their treatment it will not affect the blood test.

Needle phobia: The risks of sedation far outweigh the danger in a phlebotomy. Believe it or not, continued exposure can make things more tolerable. I've had many patients you have issues with needles, which just doesn't work in a hematologist's office. Find a simpathetic phlebotomist and don't look at anything. (that's what i do, and i'm a doctor).