Central neuraxial block

Question 1

What is the plane of injection of a spinal block?

Answer 1

Subarachnoid space, i.e. puncture of dura mater

Question 2

What is the level of injection of a spinal block?

Answer 2

Below L2 where the spinal cord ends (conus medullaris); otherwise, risk of damaging spinal cord
*Dural sac ends at level of S2!

Question 3

What is the end point of a spinal block?

Answer 3

Appearance of CSF flow

Question 4

How rapid is the onset of of a spinal block?

Answer 4

Rapid (< 5 mins)

Question 5

What is the plane of injection of an epidural?

Answer 5

Epidural space (between ligamentum flavum and dura mater), without puncture of dura mate

Question 6

What is the level of injection of an epidural?

Answer 6

Frequently inserted at thoracolumbar levels (above L2 is acceptable)

Question 7

What is the end point of an epidural?

Answer 7

Loss of resistance (to air or to saline) techniqu

Question 8

How rapid is the onset of an epidural?

Answer 8

Slower (20-30 mins)

Question 9

What are the indications for spinal anaesthesia?

Answer 9

• Lower limb surgery (e.g. hernia, THR, TKR)
• Perineal (e.g. haemorrhoids, peri-anal abscess), lower abdominal, lower segment caesarean section (LSCS)
• Upper abdominal surgery (use of spinal anaesthesia is uncommon in developed world because need a very high block 🡪 may paralyse respiratory muscles; however, it is an inexpensive option in developing countries)
• Duration of surgery: within 2-3 hours (duration of normal single shot spinal anaesthetic) (unless continuous spinal anaesthesia (CSA) which uses catheter (uncommon))

Question 10

What are the absolute C/Is to spinal anaesthesia?

Answer 10

• Patient refusal (this is only one that is truly absolute in practice, should do risk-benefit analysis for the rest)
• Infection of site of injection; severe systemic infection
• Severe coagulopathy /thrombocytopenia (most guidelines say INR < 1.4, PLT > 75 should be safe) – spinal haematoma, which, if it expands, will cause acute cord compression (and paralysis) due to confined space
• High intracranial pressure (high ICP) – risk of coning from CSF leak
• Allergy to required drug (e.g. LA allergy)

Question 11

What are the relative C/Is to spinal anaesthesia?

Answer 11

Fixed cardiac output state, e.g. aortic stenosis (In aortic stenosis, the patient requires adequate diastolic pressure to maintain coronary perfusion. Spinal anaesthesia causes sympatholytic effect with rapid vasodilation (reduces SVR, therefore reduce MAP, therefore reduce aortic root pressure. In these pts, they cannot compensate well because of the stenosis, so will become hypotensive or tachycardic without much improvement in cardiac output (leading to a vicious cycle). Decreased supply of O2 from poor aortic root pressure, + increased O2 demand from reflex tachycardia 🡪 acute myocardial ischaemia on table.

Haemodynamic instability

Spinal deformity (e.g. significant thoracic kyphosis. Many patients actually have but we don’t know – have to weigh the risk/benefits)

Active neurological disease (multiple sclerosis, demyelinating neuropathy, anything that causes diseased nerves - spinal anaesthesia itself is neurotoxic)

Immunocompromised state (we are introducing foreign material into the intrathecal space which is meant to be sterile. Doing so then increases risk of introducing infection)

Uncooperative patient (unable to keep still)

Question 12

What are the major complications of spinal anaesthesia?

Answer 12

Post-dural puncture headache (PDPH), aka “spinal headache” (when you lose CSF, it results in a loss of ICP (intracranial hypotension), causing brain to sag 🡪 traction on the meninges 🡪 headache, could possibly lead to haemorrhage

Neurological sequelae - cauda equina syndrome (CES), nerve palsies, neuritis (LA is in itself neurotoxic)

Haematoma, bleeding

Infection

Question 13

What are the minor complications of spinal anaesthesia?

Answer 13

Nausea, vomiting (N&V in spinal anaesthesia is commonly due to hypotension, which happens because the LA also blocks the autonomic pathways, causing vasodilation.

Giddiness

Shivering

Bruising and minor backache (latter not so much due to damage from injection but likely because of pre-existing back problems, e.g. lumbar spondylosis, and pain is ppt from lying there for the op)

Transient hypotension/ haemodynamic instability, sympathetic blockade

Question 14

What are the tissues you will pass through when doing a spinal anaesthesia?

Answer 14

skin > subcutaneous tissue > supraspinous ligament > interspinous ligament > ligamentum flavum > epidural space (potential space, you know you are in when there is a loss of resistance) > dura > intrathecal space