[Comparison of extrapleural and intrapleural analgesia with bupivacaine after thoracotomy].

OBJECTIVE

To compare the analgesic and the ventilatory effects as well as blood concentrations of bupivacaine, administered either in the extrapleural or interpleural space after posterolateral thoracotomy.

STUDY DESIGN

Randomized clinical trial.

PATIENTS

Twenty ASA class I and II patients, scheduled for elective thoracic surgery were randomly allocated either in the IP group (catheter inserted into the interpleural space) or the EP group (catheter inserted in extrapleural position, paravertebrally above the posterior parietal pleura).

METHODS

In the catheter, inserted at the Th4 level at the end of the surgical procedure, 20 mL of 0.5% bupivacaine were injected after full recovery from anaesthesia, with the thoracic drains clamped for 30 min. The injection was repeated every six hours. Pain was evaluated after a deep inspiration with a visual analog scale (VAS), before and 1.3 and 6 hours after the injection. Analgesia was considered as effective if the VAS score at the end of the first hour was less than 30 mm. Otherwise 0.1 mg.kg-1 of morphine was administered subcutaneously. The forced vital capacity (FVC) and the forced expiratory volume one second (FEV1) were measured preoperatively and on 1st (D1) and 2nd postoperative Day (D2). Blood samples for measurements of plasma bupivacaine concentrations were obtained at 5, 10, 20, 30, 60, 90, 120, 150, 180 and 250 min respectively after the first injection.

RESULTS

Bupivacaine provided a more rapid, deep and prolonged analgesia by extrapleural than by interpleural route. Analgesia was effective in 9 patients in EP group vs 4 patients in IP group (P < 0.05). Morphine requirements were 4 +/- 8 mg in EP group vs 17 +/- 10 mg in the IP group (P < 0.05). The FVC and FEV1 values were similarly decreased on D1, but recovery was better in EP group on D2 (P < 0.05). Bupivacaine peak concentrations in plasma were lower in EP group (0.86 +/- 0.42 microgram.mL-1) than in IP group (1.63 +/- 1.44 micrograms.mL-1), however the difference was not significant.

CONCLUSIONS

Extrapleural administration of bupivacaine provides better analgesia as the anaesthetic agent comes in closer contact with intercostal nerves and with lower risk of loss of agent through the pleural drainage. Therefore its use is recommended preferentially over the interpleural route for analgesia after posterolateral thoracotomy.