Posterior intercostal nerve block for pain relief after cholecystectomy. Anatomical basis and efficacy.

The human intercostal space has been studied by excision of the posterior part of the rib cage at autopsy, followed by fixation, decalcification, section and staining. Injection of India ink was used to simulate local anaesthetic. At a point 7 cm from the midline, the distance from the posterior aspect of the rib to the pleura averaged 8 mm. The intercostal nerve usually comprises a number of small bundles without any enclosing fascial sheath. The bundles lie in a triangular space bounded by the rib, the posterior intercostal membrane and the intercostalis intima muscle. The first two appear impervious to the spread of an injected solution, but the last permits spread of the injection round the internal aspect of the rib to gain access to the intercostal spaces above and below that into which the injection has been made. An injection of 3 ml will also spread medially to enter the paravertebral space and surround the sympathetic chain. A small clinical study gave excellent analgesia after operation for a mean duration of 12.3 h following unilateral intercostal block with 3 ml of bupivacaine 0.5% (with adrenaline) into each of the intercostal spaces T5-11, before cholecystectomy through a subcostal incision. There were no complications in the series.