Post-operative pain and analgesic requirements after paravertebral block for mastectomy: A randomized controlled trial of different concentrations of bupivacaine and fentanyl

Background: Paravertebral block (PVB) is useful for post-operative analgesia after breast surgery. Bupivacaine is used for PVB at higher concentrations (0.5%), which may lead to systemic toxicity after absorption. Therefore, we proposed to evaluate the efficacy of lower concentrations of bupivacaine with and without fentanyl for thoracic PVB in patients undergoing surgery for carcinoma breast. Methods: Forty-eight patients scheduled for surgery for breast cancer were enrolled in this prospective, randomized, double-blinded, placebo-controlled trial and were allocated to one of four groups: 0.25% bupivacaine with epinephrine 5 mcg/ml, 0.25% bupivacaine + epinephrine 5 mcg/ml with 2 mcg/ml fentanyl, 0.5% bupivacaine + epinephrine 5 mcg/ml or isotonic saline. PVB was performed and 0.3 ml/kg of the test drug was administered before induction of general anaesthesia. The primary outcome assessed was post-operative analgesic requirement for a period of 24 h. Secondary outcome measures were post-operative pain scores at rest and on movement of the arm, latency to first opioid, post-operative nausea and vomiting, quality of sleep, ability to move arm and patient satisfaction. Results: The patient characteristics and anaesthetic technique were comparable among the groups. The rescue analgesic consumption as well as cumulative pain scores at rest and on movement were significantly less in 0.25% bupivacaine+epinephrine with fentanyl and 0.5% bupivacaine+epinephrine groups (P<0.05). The average duration of analgesia was found to be 18 h after either 0.25% bupivacaine with epinephrine+fentanyl or 0.5% bupivacaine with epinephrine. Conclusions: Lower concentrations of bupivacaine can be combined with fentanyl to achieve analgesic efficacy similar to bupivacaine at higher concentrations, decreasing the risk of toxicity in PVB.