Retroperitoneal air, extracorporeal shock wave lithotripsy and epidural anesthesia.

During a 13-month period, 1,344 patients underwent extracorporeal shock wave lithotripsy. Plain x-rays done routinely 24 hours after lithotripsy to assess stone fragmentation revealed evidence of retroperitoneal air in 6 patients. All 6 patients had epidural anesthesia induced by loss of resistance to air in a syringe to identify the epidural space. It was believed likely that this was the cause of the air and 2 types of distribution were identified: 1 showed tracking of air along spinal nerves and 1 along tissue planes. This hypothesis eventually was confirmed by 2 patients in whom the air was identified after epidural anesthesia but before extracorporeal shock wave lithotripsy. Retroperitoneal air is found in a small number of patients undergoing epidural anesthesia and extracorporeal shock wave lithotripsy, and physicians treating these patients in the early postoperative period should be aware of this possible radiological finding and appreciate its benign nature.