Epidural analgesia is but one term for local anaesthetic being infused into the epidural (extradural) space. Lumbar, cervical and thoracic approaches are possible. An 18G Touhy needle is advanced through the ligamentum flavum until a loss of resistance is felt on attempted injection of air or saline. A fine catheter is passed through the needle and advanced a further few centimetres. The infusion is then started e.g. a typical example might be a mixture of 20 ml of marcaine 0.5% and 40 ml of normal saline, infused at a rate dependent on the type of surgery, the amount of pain and how long the patient is post operative. To this might be added an opioid analgesic, for example 5 mg of diamorphine, particularly in the first days after a major operation.
It is a popular form of analgesia in childbirth, but it may also be used with major thoracic, abdominal and orthopaedic surgery when the benefit is more correctly from anaesthesia.
The principal complication is gradual hypotension, caused by the loss of sympathetic tone in the lower half of the body. This is managed by stopping the infusion for an hour or two, then restarting it at a lower rate. If both analgesia and normotension cannot be achieved, it may be necessary to change the analgesia.
Complications of infusing opioids include severe respiratory depression of late-onset (up to 12 hours), nausea and vomiting, pruritus and retention. Respiratory depression can occur many hours after the start of epidural analgesia. With local anaesthetics, the epidural catheter may become misdirected into the cerebrospinal fluid. This can result in dangerous paralysis and hypotension. The patient needs to be promptly ventilated. Very rarely, dural puncture - "dural tap" - results in CSF leak.
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