· Anatomy: boundaries, contents
· Performance of block: layers, procedure, anatomical complications
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Epidural space |
· Potential space · Catheter inserted via a needle · Local anaesthetic +/- other drugs injected |
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Boundaries |
· Superior: fusion of dura to skull · Inferior: sacrococcygeal membrane · Anterior: dura mater for posterior epidural space, posterior longitudinal ligament for anterior epidural space. · Posterior: ligamentum flavum, laminae · Lateral: pedicles, intervertebral foramina |
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Contents |
Fat: · ↑ in obese · ↓ in elderly Loose areolar connective tissue: · May cause septation, patchy block Arteries: · Lateral location · Supply from spinal branch of lumbar artery · Damage -> expanding haematoma Venous plexus: · Anterior > posterior location · Drain to: lumbar veins · Engorged if uterine contraction · Risk of puncture, catheter insertion and local anaesthetic systemic toxicity (LAST) Lymphatics Spinal nerve roots |
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Midline layers |
· Skin -> fat -> supraspinous-ligament -> interspinous ligament -> ligamentum flavum -> epidural space · Further: -> dura mater -> subdural space -> arachnoid mater -> subarachnoid space |
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Midline procedure |
· Sitting and hunched · Tuffier’s line = between upper outer iliac crests = L4/5 interspace · Needle entry midway between two spinous processes · Angle anteriorly (spinous processes direct posterior) · Loss of resistance to saline on entry into epidural space |
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Anatomical complications |
· Subcut placement -> failed block · In subdural space -> unreliable, patchy · In subarachnoid space -> dense motor block, high block, hypotension, post-dural puncture headache · In epidural vein -> LAST · In epidural artery -> expanding epidural haematoma · In paravertebral space -> unilateral block |