Had a fluoro-guided spinal tap that ended up being dry. needle was put in 2 spots, but no fluid. does this happen often, even w/ fluoroscopy guidance?

An unsuccessful : spinal tap happens in a very small percentage of cases. Usually it is due to spinal deformity, severe degenerative arthritis, or inability of the patient to hold still.

Sometimes: Not commonly. Depends on several things, patient's anatomy such as spinal curvature or other osseous variation, obesity, movement of patient and sometimes experience of doctor performing procedure. Many different types of physicians with experience in lumbar puncture include anesthesiologists, interventional radiologists, neurologists, neurosurgeons, etc.