Describe Epidural Anaesthesia in detail.

Definition & Technique

Epidural anaesthesia is the injection of local anaesthetic into the epidural (extradural) space — outside the dura, so not into CSF. The epidural needle (Tuohy) is advanced until ‘loss of resistance’ identifies the epidural space, and a catheter is usually threaded to allow repeated doses or a continuous infusion. It can be performed at any level (lumbar, thoracic).

Differences from Spinal

Because the drug is deposited outside the dura, epidural anaesthesia needs a much larger volume/dose of local anaesthetic, has a slower onset (10–20 min), and produces a block whose height can be controlled by the volume and catheter level — often a segmental band of anaesthesia. The catheter allows the block to be topped up or prolonged, and a lower concentration gives predominantly sensory (analgesic) block.

Uses

Epidurals are widely used for labour analgesia (low-concentration LA ± opioid, preserving some mobility), for intra-operative anaesthesia (often combined with general anaesthesia for major abdominal/thoracic surgery), and for postoperative analgesia via a catheter infusion. The controllability and catheter are their great advantages.

Combined Spinal–epidural

A combined spinal–epidural (CSE) gives the rapid, dense onset of a spinal together with the flexibility of an epidural catheter for prolongation and postoperative analgesia — popular in obstetrics and major surgery.

Loss of Resistance & Catheter Care

The epidural space is identified by the loss-of-resistance technique: as the Tuohy needle passes through the dense ligamentum flavum the resistance to a syringe of saline or air is suddenly lost as the needle tip enters the epidural space, and the catheter is then threaded a few centimetres and secured. Because the catheter stays in place for hours or days, its care matters — it is kept sterile and clearly labelled to avoid the disastrous error of injecting the wrong drug, the infusion is monitored, and the block height and the patient’s neurology and vital signs are checked regularly so that complications such as an ascending block, catheter migration or early haematoma are detected promptly.

Segmental Block & Concentration

A distinctive feature of epidural anaesthesia is that the block can be made segmental, covering a band of dermatomes around the catheter tip rather than everything below a level, and its character can be adjusted by the concentration of local anaesthetic used. A higher concentration produces dense sensory and motor block suitable for surgery, whereas a low concentration — often combined with an opioid — gives predominantly sensory analgesia that spares motor power, which is exactly what is wanted for a labouring woman who needs pain relief while remaining able to move, or for a postoperative patient who needs analgesia without being unable to mobilise. This ability to titrate both the height and the density of the block is one of the epidural’s greatest strengths.

Slower onset than spinal but allows continuous top-up.

• Epidural: LA into the epidural space (outside dura), identified by loss of resistance; catheter usual.
• Vs spinal: larger dose/volume, slower onset, controllable/segmental height, top-up via catheter.
• Uses: labour analgesia (low-dose LA ± opioid), adjunct to GA for major surgery, postoperative analgesia.
• Risks: dural puncture (→ possible total spinal) & intravascular injection — use a test dose, aspirate, dose incrementally.
• Combined spinal–epidural: fast dense spinal + catheter flexibility.