Single-injection thoracic paravertebral block and postoperative analgesia after mastectomy: a retrospective cohort study

•We examined patients who underwent either unilateral or bilateral mastectomy.•We determined the duration and degree that thoracic paravertebral nerve block provides postoperative analgesia.•We examined the numeric rating scale for pain scores from 182 individual patient hospitalizations.•Thoracic paravertebral nerve block provides postoperative analgesia in the immediate postoperative period after mastectomy.•Thoracic paravertebral nerve block does not provide postoperative analgesia after the first day of surgery.