You are on shaky ground even if you get the patient to sign a waiver. Aside from the standard of care argument, attorneys can find many ways to argue assumption of risk. If you are sued, be ready to spend lots of time preparing for and attending depositions. Your insurance company will have to pay for the defense even if you ultimately prevail.
Bottom line, don't do it just because you can. There are lots of things you CAN do that you SHOULDN'T do.
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