The drugs are injected into the cerebrospinal fluid that bathes the spinal cord. In order to do that the needle makes a tiny hole in the dura, which is a tissue encasing the spinal cord and the cerebrospinal fluid. Small doses of local anaesthetic are required because they spread more easily in the spinal fluid. With an epidural block, the drugs are delivered outside the dura, in the epidural space, hence the name for the block. Occasionally, the dura can be inadvertently breached in performing an epidural block, known as a dural puncture. Larger doses of local anaesthetic are required because the spread is through tissues rather than fluid.