In my understanding, I am sure wintermute will clarify if I get this wrong.....
A case is the pre and post care along with the actual surgery. You have to assess the patient pre-op, go home and research the procedure, the surgical technique, and any possible interactions those two might have. You have to choose the anesthestic to be used, and generally get ready for surgery the next day. During the case you do the induction, (secure an airway, administer anesthetic) and maintain the patient throughout the surgery. Afterward you awaken the patient and recover them. Give report to the receiving nurse and follow up later.
Surgeries can be as short as 30 minutes, or as long as an entire day. That is why wintermute stated that hours did not matter.
As far as difference in education, well for one you don't have to go to medical school. You as a result will not have the depth of general knowledge that an MD has. This is why it is critical to get good experience before you enter a program. Time wise, they are about the same with 2 years diference.
4 years undergrad, 2-3 years working experience, 3 years graduate school = 10 years. for CRNA
4 years undergrad, 4 yeas Medical school, four years residency, = 12 years
for MD Anestheiologist.
An anesthesiologist has more options in their scope of practice, as they can work pain service and become ICU intiensivists. While CRNA's only have the ability to practice in the OR.
I hope that helped.
Oh the biggest difference from MD to CRNA is pay, as a CRNA, you will make 1/3 of the what the MD does.