What happens if a lumbar puncture is done too high?

May hit cord. Doing an LP too high up in the back risks hitting the spinal cord, which can damage the cord. It is best to do an LP below the level where the actual spinal cord ends since the needle is designed to slide by nerve roots.
Higher risk injury. Lp s are done in the lumbar region because the spinal cord tapers and there is less likelihood of hitting it. Furthermore it is a better place to collect the spinal fluid.