Unfortunately, I have to recommend a Surface Pro 3.
You need full Windows, most likely.
And the Macbook Air does not have pen input.
This is one of those circumstances that such a device will be favourable. If you can get past the fact that it runs Windows, but again, you have little choice.
Battery Life will not be as good as your MacBook- expect 5-7 hours in normal (light) usage.
The Pen will be very useful. For signing documents, etc. My recommendation is to get the type cover; the touch cover is only good for brief usage.
You'll want an i5, 256GB model most likely. This will not be cheap; you'll be paying about $100 more for an equivalent MacBook. If you can live with less storage, you can get the cheaper 128GB model.
I don't know what software you need, nor am I involved in the medical community. But I can image a pen, running the software you need, and a tablet form-factor would be more favourable than a MacBook Air in this case.