The problem with this is that except for some really routine stuff, a lot of operations are really custom-tailored to the patient. This might be a 100th time the surgeon is removing a certain type of tumor, but first time doing it in an obese person, or a child, or someone with rare blood condition, or million other things. Once you get to the real life-saving stuff no two operations are the same, even though on paper they might seem like they are. That's why it's hard to put a number on it.