You are encouraged to get a second opinion before any surgery unless it is emergency surgery; even on Medicare. You should ask that your records be sent to the doctor offering a second opinion in advance. Thereafter, you will be responsible for 20% of the cost of the visit.
First, check with your plan provider to determine the requirements for a seond opinion and to determine if only certain doctors can been seen because you definitly want the process covered.
You will need to speak with a licensed insurance professional who is licensed for life and health insurance, and one who has experience dealing with Medicare insurance coverage.
Medicare covers 2nd and 3rd opinions provided that the procedure is not an emergency surgery. Otherwise, Medicare pays for 4/5 of the approved amount for these opinions.