A Randomized, Double-blind Comparison of the Effects of Interpleural Bupivacaine and Saline on Morphine Requirements and Pulmonary Function after Cholecystectomy

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Abstract
The effect of interpleural bupivacaine and saline placebo on morphine requirements and pulmonary function after cholecystectomy was investigated. Twenty-six patients were randomly assigned on postoperative day 1 to receive either 20 ml preservative-free saline (group 1) or 20 ml 0.5% bupivacine with epinephrine, 5 .mu.g/ml (group 2) through an interpleural catheter. Adequacy of pain relief was determined by the amount of morphine used by the patient following interpleural injection. Morphine use via a patient-controlled analgesia (PCA) system was recorded for several hours before and after interpleural injection. All patients had a forced vital capacity (FVC) and FEV1 measurement immediately before and 1 h after interpleural injection. Mean hourly PCA morphine use ranged from 1.6 to 2.8 mg for the 6 h prior to interpleural treatment for groups 1 and 2. There was no difference in PCA use between the groups during this time. Group 1 patients did not reduce PCA morphine use after interpleural saline. Patients in group 2, however, significantly reduced PCA morphine use after interpleural bupivacaine. Mean PCA morphine use for group 2 was 0.38 .+-. 0.15 mg/h (mean .+-. SE) (81% reduction vs. control) for the first 2 h after bupivacaine (P < 0.05). Mean PCA use in group 2 was 0.52 .+-. 0.2 mg/h (73% reduction vs control) for the third hour after bupivacaine (P < 0.05). At the fourth and fifth hours after bupivacaine injection, mean PCA morphine use was not significantly different from that in group 1. FVC and FEV1 did not improve after interpleural saline. In group 2 FVC increased from 1.29 .+-. 1.76 .+-. 0.11 (P < 0.06) after interpleural bupivacaine, whereas FEV1 improved from 0.97 .+-. 0.1 to 1.53 .+-. 0.15 l (P < 0.05). In summary, interpleural bupivacaine significantly reduced PCA morphine requirements, and this effect lasted approximately 3 h. Interpleural bupivacaine also had a favorable effect on FVC and FEV1.