Efficacy of topical anesthesia on post-thoracotomy ipsilateral shoulder pain

Background. Ipsilateral shoulder pain (ISP) is a common problem and a risk of respiratory complications after thoracic surgery. ISP is an often severe and poorly controlled by epidural and opioid analgesia. It is thought to be a referred phrenic pain. The aim of the study was to investigate the efficacy of anesthetizing the skin overlaying the referred pain area in a randomized, double-blind fashion. Materials and Methods. Fourtyfive consenting adult patients undergoing elective thoracic surgery participated to study. All patients received standard general anesthesia and midthoracic epidural and, upon randomization, one of the following topical treatments: 1) A placebo cream on the referred phrenic pain areas (placebo cream group); 2) Two-three g of an eutectic mixture of lidocaine 2.5% and prilocaine 2.5% (EMLA, Astra-Zeneca, Basiglio, Milan, Italy) on homologous, contralateral thoracic areas (placebo site group); or 3) Two-three g of anesthetic cream on ipsilateral referred phrenic pain areas (active group). Rectal indomethacin and IV pethidine were rescue analgesics. Pain intensity was assessed over a 0-10 Numeric Rate Scale and consumptions of analgesics were recorded at postoperative 0, 1, 2, 3 and 24 hours. Categorical data were analyzed by a χ2 test and continuous variables by a Bonferroni corrected t test. Results. There was not difference in age, weight and type of surgery across the groups. ISP (NRS > 3) was reported in larger numbers of patients in the placebo cream group and in the placebo site group than in the active group (7 and 9 patients vs. 2 patients, P = 0.03 and P = 0.01). During the first postoperative day and compared to the placebo cream group and placebo site group, the active group had lower pain intensity (table 1) and lower consumption of indomethacin (122.5 mg ± 35.3 and 114.3 mg ± 50.1 vs. 20.2 mg ± 31.3, P = 0.01 and P = 0.03) and of pethidine (25.2 mg ± 5.1 and 23.5 mg ± 3.5 vs. 8.3 mg ± 2.5, P = 0.0001 and P = 0.001). No side effect was observed from the anesthetic cream apart mild skin irritation in 4 patients in the active group. Discussion. Topical anesthesia was highly effective in preventing post-thoracotomy ISP. The findings suggest that in most thoracotomy patients ISP is transmitted via the phrenic nerve.