Grunt Doc has a great post about an ED physician who used an "over-the-counter" power drill to drill a hole in a patient skull and relieve pressure caused by an intracranial bleed. I've thankfully never had to perform this procedure.
The first instruction from a how-to paper.
(1) A sense of historical proportion. Drilling a hole in the head is
just the boring (sorry) start to most neurosurgical days. Trephination was
practised safely in the Stone Age. So relax