Confirmation of location of epidural catheters by epidural pressure waveform and computed tomography cathetergram

Abstract

Objective: Epidural pressure has remained a relatively unused test of physiological monitoring for the past 3 decades. It is our hypothesis that epidural pressure waveforms (EPWFs) obtained by transducing an epidural catheter (EC) can be used as a surrogate for the accurate location of the EC. The goal of this study was to validate this new method by comparing it with a more objective radiographic technique such as computed tomography cathetergram (CTC). Methods: The EPWF and CTC were studied in 13 patients receiving continuous epidural analgesia (12 patients who had postoperative pain and 1 patient who had chronic pain). Of these 13 patients, 8 patients had reported inadequate analgesia, and 5 had reported satisfactory analgesia. First, the end of the EC was connected to a disposable pressure transducer, this was followed by a 5-mL normal saline bolus injection to ensure the patency of the EC, and the EPWF was recorded. Next, the patient was taken to an imaging suite and, after injecting contrast through the EC, the course of the catheter was imaged with computed tomography (CT). The CT images were studied by the neuroradiologist and correlated with the EPWF. Results: The EPWF of 5 patients with clinically adequate analgesia revealed a pulsatile waveform on transducing the EC and a crescentic spread of contrast in the epidural space on CTC. In 8 patients with inadequate epidural analgesia, the EPWF measurement failed to show oscillations, and contrast collections were observed in the paraspinous muscles. The results of EPWF and CTC were compared using Fisher's exact test. Conclusions: The strong relationship between EPWF and CTC suggests that EPWF can be used reliably to confirm the correct placement of the EC in a selected group of patients. Reg Anesth Pain Med 2001;26:337-341.