Answer:
   
   There is an over-riding principle in Judaism (every movement) that any
   Jewish law can be broken when it comes to saving a human life. The
   only exceptions are for idolotry, adultery, or murder. These are the
   only situation in which is Jew must choose death to avoid violating
   the law.
   
   So, when looking at medical procedures, one must first ask whether the
   procedure must be done immediately (or at least during Shabbat) in
   order to save a life.
   
   Let's look at one example: Rehabilitation treatment. In some
   situations, this treatment consists of music and dance and arts and
   crafts. These are not likely to be "life-saving", although some could
   be. On the other hand, if the treatment is physical and medical
   rehabilitation (for example, cardiac rehab after surgery, exercises
   for burn victims to keep their muscles from constricting, etc.) that
   is probably a different story.
   
   Note that this isn't just a Reform view. Even in the traditioanl view,
   the definition of life saving is broader than one might assume. It
   includes preventing someone from being alive but immobile, or deaf (in
   the case of hearing aids), blind, or if it threatens sanity. Life
   means productive life. Also if the procedure would measurably lengthen
   life expectancy, one can be lenient.
   
   The basic answer is to
    1. Talk to the physician to see if the treatment is absolutely
       necessary to save a life. If so, do it. No questions.
    2. Talk to the individual to see if s/he considers the activity work
       and if it is if his/her's movement prohibits it on Shabbat.
       Although this FAQ is geared towards the traditional viewpoint, the
       patient may be of one of the non-traditional movements.
    3. If time permits, consult with the individual's rabbi. If the issue
       is of concern to the patient, their rabbi will be glad to talk to
       you.
       
   Note that some say that an observant Jewish doctor cannot attend to a
   Christian on Shabbat, based on the claim that Christians are
   idolaters. This is untrue, for three reasons:
    1. Tosafos rule that Christians are not idolaters. Noachides who
       believe that God has partners are not considered idolaters, they
       are viewed as merely mislead. They opine that the trinity assigns
       to partners to the Father who they identify with our God. This is
       the ruling followed in the jewelery industry, allowing Jews to
       sell crosses and crucifixes for wear by people who are presumably
       non-Jewish.
    2. Even if not, there is a concept of saving non-Jewish lives so as
       to reduce animosity. An idolater saved on Shabbos makes it more
       likely someone of his community would save a Jew. For that
       hypothetical Jew, he may violate Shabbos.
    3. There is a concept of "derech shalom"--ways of peace, part of the
       obligation of imitatio dei. It too requires saving people of all
       stripes. Note that unlike reason number 2, this makes saving a
       non-Jew an ideal no less than that of saving a Jew.