Things like: chest pain, any new pain, SOB, changes in VS like very low or very high HR or BP, fever, a patient who is suddenly not able to pee at all for no reason, an abdomen that suddenly feels firm and distended, if a patient is having a reaction to a medication, etc...Hope that helps. Anything that is abnormal and unusual for the patient and/or is life-threatening. When in doubt, it's better to call the physician than not. That's my motto anyways.