[Accidental catheterization of the subdural space. Confirmation by radiological study]

We report two cases of accidental subdural blockade after peridural anesthesia. The blockade was detected postoperatively in both cases, two hours after start of continuous perfusion in one patient and eight hours afterwards in the other. Subdural diffusion was confirmed after injection of a radiopaque contrast medium. Subdural blockade usually manifests as an extensive neural block that is disproportionate to the amount of anesthetic injected. We discuss the need for frequent monitoring of metameric, sensory and motor levels to detect possible catheter misplacement, in addition to routine monitoring of heart rate, arterial pressure and oxygen saturation. When subdural blockade is suspected, epidural perfusion should be discontinued in order to prevent extensive sensory and motor blocks. A firm diagnosis can only be made by X-ray. A simple radiograph may adequately demonstrate subdural placement in some cases, although computed axial tomography should be performed when doubt arises.