Randomized double-blind comparison of phrenic nerve infiltration and suprascapular nerve block for ipsilateral shoulder pain after thoracic surgery

Abstract

Despite the use of thoracic epidural analgesia, a constant severe ache occurs in the ipsilateral shoulder of almost 75% of patients after thoracotomy. The aim of this prospective-randomized study was to investigate the effect of phrenic nerve infiltration (PNI) compared with suprascapular nerve block (SNB) on ipsilateral shoulder pain after thoracic surgery. After Local Research Ethics Committee approval, written informed consent was obtained from 90 adult patients undergoing thoracotomy for pulmonary resection. Patients were excluded if they had preexisting shoulder pain, were unable to understand the visual analog scale (VAS) scoring system or due to failure of epidural analgesia. The phrenic group (PNI) received 10 ml of 2% lidocaine infiltrated into the periphrenic fat pad, 1-2 cm close to the diaphragm, just before chest closure. The suprascapular group (SNB) received 10 ml of 0.5% plain bupivacaine injected into the suprascapular fossa once the surgery was finished. A blinded observer to the study group assessed the patient's shoulder and thoracotomy pain, using the VAS score and a five-point observer verbal rating score (OVRS), at 0.5, 1, 2, 3, 4, 5, 6, 12, 48, and 72 h after surgery and at discharge. The time and dose of any administered analgesic medication were recorded. Finally, 74 patients were included (37 per group). Sixteen patients were excluded (unable to understand scoring system, failure of the epidural technique, and lost data). There were no significant differences in age, gender, body mass index, type/duration of operation, and pain scores at rest, between the two groups. Shoulder pain intensity was significantly lower in the PNI group compared with the SNB group (median value of VAS area under the curve for the PNI group: 8.1 (0-70.9)cm vs 114.3 (43.8-193.8)cm for the SNB group; p < 0.001). There were no significant differences between the two groups according to postoperative thoracotomy pain. Phrenic nerve block with 2% lidocaine should be performed in all patients undergoing a major thoracic surgery procedure. These results strongly support the hypothesis that irritation of the pericardium and/or mediastinal-diaphragmatic pleural surfaces results in pain that is referred to the shoulder via the phrenic nerve.