Who makes medical decisions if the president is in a coma?

[President Johnson]

I think this a very interesting question: Who makes medically related decisions for the president if he or she is in a coma? The president's spouse, the vice president, or the doctors alone?

In my novel, I have an interesting scenario: The president is in a coma following an assassination attempt, 25th Amendment gets invoked. At a certain point, a second surgery must take place to remove certain bullet fragments from his chest. However, the First Lady - who is at odds with the president's inner circle - insists the surgery takes place in a Las Vegas Hospital (where the shooting occurred), but the vice president - acting as president - wants to move her boss to Walter Reed for the surgery. Who in this case would make the decision? Or is it the doctors themselves? But even in this case, the vice president should have authority over them?

[President Johnson]

In the absence of a living will or an advance directive from the President, spouses are usually the ones who get to make medical treatment decisions. If a spouse &/or children don't exist or aren't available, then - depending on the jurisdiction - a "close friend" familiar with the person's values (i.e. possibly the Vice President/Acting President in this scenario) can make the decision, & some jurisdictions have developed mechanisms for "unbefriended" patients, usually involving choices by designated physicians (e.g., the President's doctor, the official physician to the President, etc.) often in conjunction with other physicians (presumably a medical team) &/or ethics committees.

The question though is whether there isn't an advanced national interest at stake, and the First Lady or First Gentleman has no jurisdiction to make such decisions. I guess it could be tested before court if a disagreement were ever to occur.