Continuous Infusion of Interpleural Bupivacaine Maintains Effective Analgesia After Cholecystectomy

Twenty-five patients who had undergone elective cholecystectomy were prospectively randomized to receive via an interpleural catheter either a continuous infusion of 0.25% bupivacaine at 0.125 mL·kg−1·h−1 (n = 13) or repeated bolus injections (n = 22) of 0.5% bupivacaine with epinephrine 1:200,000 at 0.4 mL/kg every sixth hour. Adequacy of pain relief was measured by the amount of patient-controlled analgesia morphine required postoperatively and by patient scores on a visual analog scale obtained every sixth hour. Two venous blood samples for measurements of serum bupivacaine levels were obtained from patients in the continuous group at hours 6 and 24; four blood samples were obtained from patients in the bolus group, both immediately before and 30 min after injections at hours 6 and 24. Among the patients receiving the bolus injections, morphine was required 62 ± 15 (SEM) times over the 24-h study period with total morphine dosage averaging 30 ± 15 mg. Corresponding values for patients in the continuous group were 35 ± 10 times and 23 ± 5 mg of morphine. The difference was not, however, statistically significant, but when activity during the 2-h time periods immediately before reinjection ere examined, patients in the bolus group required and received significantly more morphine than did those in the continuous group (P<0.05). Patients in the continuous group had visual analog scale scores that averaged 2.9 ± 0.6 over the 24-h study period. Patients within the bolus group had visual analog scale scores before and again 30 min after injection that averaged 5.8 ± 0.8 arid 1.8 ± 0.5, respectively (P<0.05). Serum bupivacaine levels increased in both groups between the sixth and 24th hour measurements; the average postinjection bupivacaine levels were significantly higher (P<0.05) with intermittent injection than corresponding levels in the continuous infusion group. The bupivacaine level rose to 3.2 ± 0.4 μg/mL 30 min after the bolus injection at hour 24. In summary, continuous interpleural infusion of 0.25% bupivacaine provides safer and more effective postoperative pain relief after cholecystectomy than does intermittent interpleural injection of 0.5% bupivacaine with epinephrine every 6 h.