Continuous intercostal nerve blockade. An anatomical study to elucidate its mode of action

India ink was injected through extradural catheters placed in the posterior intercostal space in 12 cadavers undergoing autopsy and the subsequent spread of the India ink was assessed under direct vision. The ink spread subpleurally to reach a number of intercostal spaces and medially to reach the paravertebral space. It is concluded that analgesia extending over a number of dermatomes is achieved by subpleural tracking of local anaesthetic to reach intercostal nerves above and below the one injected.