We have undertaken a prospective, randomized comparison of the superficially similar techniques of interpleural and paravertebral (extrapleural) analgesia in 53 patients undergoing posterolateral thoracotomy. Local anaesthetic placed anterior to the superior costotransverse ligament and posterior to the parietal pleura produces a paravertebral block and instilled between the parietal and visceral pleurae produces an interpleural block. Patients received preoperative and postoperative continuous bupivacaine paravertebral blocks in group 1 and interpleural blocks in group 2. Premedication comprised diclofenac and morphine, and after operation all patients had regular diclofenac and patient-controlled morphine (PCM). Analgesia was assessed by visual analogue pain scores (VAS), PCM requirements, ratio of preoperative to postoperative spirometric values (PFT), rates of postoperative respiratory morbidity (PORM) and hospital stay, all recorded by blinded observers. Eight patients were withdrawn and data from 45 patients were analysed. Patient characteristics, surgery, VAS scores and PCM use were similar in both groups. PFT were significantly better (P = 0.03-0.0001) in group 1, and PORM was lower and hospital stay approximately 1 day less in this group. Five patients in group 2 became temporarily confused, probably because of bupivacaine toxicity (P = 0.02). We conclude that bupivacaine deposited paravertebrally produced greater preservation of lung function and fewer side effects than bupivacaine administered interpleurally.
