עבודת רופא בשבת

The question below is for Rabbi Avraham S. Avraham:

May a person choose to be a doctor knowing in advance that his position will involve working on Shabbat, albeit with pikuach nefesh in every instance? Must he choose a specialty that would allow him to not have to do work on Shabbat? If he is a doctor, must he accept less money to work if his non-Jewish partners will not allow him to take off every Shabbat otherwise? If he is working on Shabbat, can he drive to the hospital and do things as he would normally do on the weekday?

I greatly appreciate your spending time on this question. If the answer is too involved for email, I would be grateful if you could speak to me on the phone.

Thanks.