Retroperitoneal Air and Extracorporeal Shock Wave Lithotripsy

Abstract

Over a 13-month period, 1,344 patients underwent extracorporeal shock wave lithotripsy (ESWL). Plain x-rays (KUB) were done routinely 24 hours post-ESWL to assess stone fragmentation. Six patients were noted to have retroperitoneal air (RA) on these films. All six had epidural anesthesia (EA) induced using “loss of resistance to air in a syringe” to identify the epidural space. Four patients had unilateral ESWL and two had bilateral. The number of shocks delivered to each kidney ranged from 500 to 3,800 at 18 to 22 kV. All stones were satisfactorily fragmented and postoperative courses were uneventful. Classically RA is associated with colonic perforation or retroperitoneal infection; tissue damage to lung or colon by shock waves could lead to tracking of air along tissue planes producing similar x-ray findings. None of these causes was apparent in our patients. A final possibility could be the introduction of air into paraspinal tissues or along spinal nerves during induction of EA. This explanation is supported by the fact that the RA was not necessarily on the same side as the stone and is further substantiated by a recent patient who developed RA on a KUB 30 minutes after EA but before ESWL. In conclusion, RA is found in a small number of patients undergoing EA and ESWL. It is likely introduced during induction of EA, and urologists treating these patients in the early post-ESWL period should be aware of this possible radiological finding and appreciate its benign nature.