The Nurse Is Preparing to Assess a Patient's Pain Level

The nurse is preparing to assess a patient's pain level.Which definition of pain should the nurse use to guide practice?

A) Pain is whatever the experiencing person says it is.
B) Pain is an unpleasant sensation caused by physical injury.
C) Pain is a sensation that causes the patient to avoid its source.
D) Pain is discomfort manifested by elevated vital signs and grimacing.