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Background: The use of large doses of opioid analgesics to treat pain after cardiac surgery can prolong the time to tracheal extubation and interfere with recovery of bowel and bladder function in the postoperative period. Therefore, the authors investigated the efficacy of a continuous infusion of bupivacaine 0.25% or 0.5%, at the median sternotomy site, for 48 h after cardiac surgery in reducing the opioid analgesic requirement and improving the recovery process. Methods: In this prospective, randomized, placebo-controlled, double-blind clinical trial, 36 consenting patients undergoing open-heart surgery with a standardized general anesthetic technique had two indwelling infusion catheters placed at the median sternotomy incision site at the end of surgery. The patients were randomly assigned to receive normal saline (control), bupivacaine 0.25% or bupivacaine 0.5% via an elastomeric infusion pump at a constant rate of 4 ml/h for 48 h. Patients evaluated their chest pain using an 11-point verbal rating scale, with 0 � no pain to 10 � worst pain imaginable. In addition, the postoperative opioid analgesic requirements and opioid-related adverse effects were recorded. Patient satisfaction with their pain management was assessed at specific intervals during the postoperative period using a 100-point verbal rating scale, with 1 � highly dissatisfied to 100 � highly satisfied. Finally, serum bupivacaine concentrations were measured 24 and 48 h after surgery. Results: Compared with the control group, there was a statistically significant reduction in verbal rating scale pain scores and patient-controlled analgesia morphine use in the bupivacaine-0.5% group. Patient satisfaction with their pain management was also improved in the bupivacaine-0.5% (vs. control) group. However, there were no significant differences in patient-controlled analgesia morphine use between the bupivacaine-0.25% and control groups. Although the duration of the intensive care unit stay (30 vs. 34 h, respectively) was not significantly decreased, the time to ambulation (1 � 0.5 vs. 2 � 1 days, respectively) and the duration of hospital stay (4.2 vs. 5.7 days, respectively) were lower in the bupivacaine-0.5% group than in the control group. Mean � SD serum bupivacaine concentrations at 48 h in the bupivacaine-0.25% and bupivacaine-0.5% groups were 0.5 � 0.5 and 1.3 � 0.7 �g/ml, respectively. Conclusion: A continuous infusion of bupivacaine 0.5% at 4 ml/h is effective for decreasing pain and the need for opioid analgesic medication as well as for improving patient satisfaction with their pain management after cardiac surgery. Patients in the bupivacaine-0.5% group were able to ambulate earlier, leading to a reduced length of hospital stay.