Modifier 58 is appended to a surgical service to indicate that the physician performed a procedure during the global period that was planned at the time of the original procedure (staged), was more extensive than the original procedure, or is the therapeutic service following a diagnostic procedure.  Modifier 78 is used for a related trip to the OR that was unplanned, and modifier 79 for a return, unrelated trip to the OR.  

A new postoperative period begins with the second procedure.

Use this modifier when the second procedure was planned.

A common example is when the physician performs a biopsy with a ten day global period, and then takes the patient back to surgery to treat the problem found on biopsy.