Retroperitoneal Air and Extracorporeal Shock-Wave Lithotripsy
Over a 13-month period, 1,344 patients underwent extracorporeal shockwave lithotripsy (ESWL). Plain x-rays (KUB) were done routinely 24 h post-ESWL to assess stone fragmentation. Six patients were noted to have retroperitoneal air on these films. All six patients had an epidural anesthesia induced using “loss of resistance to air in a syringe” to identify the epidural space. Four patients had unilateral ESWL and two had bilateral ESWL. The number of shocks delivered to each kidney ranged from 500–3,800 at 18–22 kV. All stones were satisfactorily fragmented and post-operative courses were uneventful. Classically, retroperitoneal air 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 the epidural anesthesia. This is supported by the fact that the retroperitoneal air was not necessarily on the same side as the stone. It is further substantiated by a recent patient who developed retroperitoneal air as seen on the KUB 30 min after epidural anesthesia but before ESWL.