Cytopathologic examination of epidural catheter for postoperative analgesia. Pathophysiology and clinical management

The authors performed a prospective study in a series of patients undergoing combined general and epidural anaesthesia for major abdominal surgery in order to define if the epidural catheter inserted for postoperative analgesia induced in the short-term (7-8 postoperative days) any cytopathologically appreciable inflammatory response.

From April to September 2001, 20 consecutive patients undergoing combined general and epidural anaesthesia for major abdominal surgery at the National Cancer Research Institute and Villa Scassi Hospital (Genoa), were recruited after obtaining Institutional Ethics Committee approval and written consent from the patients. The standard technique for epidural anaesthesia was adopted. Preoperatively, all patients received peridurally a dose test of 3 ml of 2% lidocaine (60 mg) followed by 5 ml of ropivacaine 0.75%, and a continuous infusion of ropivacaine 0.375% (5-10 ml/h; maximal dose=20 ml) intraoperatively. As regards the therapeutic management of postoperative analgesia, patients received a continuous infusion of ropivacaine 0.2% for at least 48 hours and supplemental bolus (2 mg/die) of morphine hydrochloride. The epidural catheter was always removed between the 7th and 8th postoperative day, and it was examined by the pathologist according to the Thin Prep 2000 procedure.

The cytopathologic examination of the tip of the epidural catheter gave the following findings: amorphous material without cells (n=10); rare granulocytes and histiocytes (n=6); stromal cells (n=3), and rare lymphocytes (n=1).

We were unable to detect any cytopathologically appreciable inflammatory response at the tip of the epidural catheter which could have suggested the occurrence of inflammation in the epidural tissues. Given the positive results of prophylactic epidural administration of small doses of corticosteroids in the reduction of postepidural anaesthesia back pain and their direct membrane action on nociceptive C-fibers, this kind of backache seems to be related to the stimulations of such nociceptors more than to a catheter-related inflammatory response of epidural tissues with possible evolution in peridural fibrosis, as reported following surgical intervention for lumbosacral disease.