Power
You have the power to make medical decisions that'll save lives. And not just one or two—your work will affect dozens, hundreds, or even thousands of people during a single mission. As part of a team of doctors, you're all in charge in the event of any medical emergencies (which will be, like, literally all the time).
So you can point to an underling nurse and start barking directions at him, but it probably won't feel all that powerful. Most likely because you'll be frantically trying to save a life at that moment.
The powerful thing in this conversation, really, is the medicine. Doctors at work for MSF deal with all sorts of scary situations—mortal wounds, highly infectious diseases, lethal viruses—but they also deal with a lot of relatively simple medical problems that their patients don't have the money or resources to solve on their own.
Treating such patients is so routine for the doctors they could probably do it in their sleep, but it's the medicinal know-how that's the most necessary ingredient in the recipe. And it's a pretty powerful ingredient.