Technically, you can pick whatever you want as a pt identifier--random number, MR#, SSN, birthdate, etc.
At my program, we always use MR#s. For cases where two residents are taking credit (i.e. a bilateral mastectomy and each had their own side), one resident does the MR# and the other will add a zero to the MR# or do the MR# backwards (the Op Log will not allow two residents to take credit for a patient on the same day, unless one of them logs as TA).
To those who are new to case logging, a few hints:
1. Keep up with your logging. If you don't, when you lose your book or the stack of stickers with your cases that haven't yet been logged, you will wish you had. Someone in my program lost 4 months worth of cases to log when someone else decided to 'clean up' the area where she kept her stuff. Oops. I try to do it at least weekly, but will do it more often if I remember.
2. Keep track of minor procedures (lines, chest tubes, etc.) and log them. Some hospitals will want this info for privilege purposes, depending on hospital policy and your chosen field (esp. if you subspecialize or jump to another field)...and by the time you are senior, you probably won't be thinking to log these types of things anymore. Thus, log enough of them when you're still a junior to compensate.
3. Follow the policy your program has for taking credit--i.e. if surgeon junior, is that 50% of the case done by the resident? 75%? 90%?
4. Keep track of critical care stuff, and log it. Directions on how to log these cases is in the OpLog program itself. You don't want to get to the end your chief year and realize that you didn't save any stuff from your 9 months of ICU as a PGY2 when you were racking up the critical care patients. Of course, you could make something up, but if your OpLog is audited, you're screwed.
5. If you do multiple things during the same case, enter all things you do. "Mark" the one that's "worth" the most---i.e. one that gives you category credit or one that gives you category credit in an area in which you are still deficient.
That's all I can think of for now, but others may have a few more tips...
