Mechanism of action of extradural analgesia

The factors governing the spread and site of action of local anaesthetics in the extradural space are discussed. Local anaesthetic drugs injected into the extradural space may cause nerve blocks at three possible sites: (a) On the spinal nerves in the paravertebral space. This probably occurs only in young subjects. (b) On the spinal nerves intradurally. This is probably the essential site of blockade. (c) On the spinal cord.