Over the years, I have assisted in many medical emergencies on board. On virtually every occassion I was asked to show credentials ( I always carry credit card sized medical license with me). I have never asked for or expected any compensation for what I would consider a professional obligation to help someone in need. Most times, however, the airline has acknowledged this assistance in some way.
Delta- upgrade certificates for international in the days when they still had system wide upgrade certificates.
Lufthansa- upgrade to int . FC on return plus a card from the VP with a very nice book in addition to champagne bottles on the flight where I actually assisted.
Cathay Pacific- upgrade to First on return from BOM all the way back to LAX plus an invite to sit with the pilots on the 747 in the cockpit for 45 min or so (obviously this was pre 911)
Northwest- nada ( I sat with the passenger and monitored her for 4 hours and avoided a diversion of the plane).
American- miles and a thank you card