Purpose: We examined whether or not the spreading pattern of contrast dye through the catheter into the thoracic paravertebral space (TPVS) was associated with acute post-operative pain relief after breast cancer surgery. Methods: Sixty patients were recruited. After surgery, patients received thoracic paravertebral block (TPVB). The catheter was inserted within the TPVS, and radiographic contrast dye was injected through the catheter. Based on the main spreading patterns of the dye, the patients were divided into a cloud-like (spreading to the posterior compartment of the TPVS) or a longitudinal spread group (spreading to the anterior compartment of the TPVS). The primary endpoint of the study was pain intensity by numeric rating scale (NRS) and additional analgesic requirements within 12 h after surgery. Results: In 22 patients, the spread of contrast dye was not noted in the PVS. Of the 38 eligible patients, 9 patients were assigned to the cloud-like spread group, 28 patients to the longitudinal spread group and 1 patient was excluded. There were no significant differences in the NRS between the two groups both at rest and on moving. No significant differences were found in the frequency of requiring additional analgesics. Conclusions: There is no marked difference in the analgesic efficacy after breast cancer surgery based on the spread of the contrast dye to the posterior or anterior compartment of the TPVS. We should not insert the needle deeply within the TPVS, as the risk of the migration of catheters into the pleural space can be quite high.

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