"Regional & Spinal Anesthesia" — Practice

Question 1

The sensory level required for caesarean section under spinal anaesthesia is

Accepted Answer

D

Question 2

The property of a local anaesthetic that determines its speed of onset is

Accepted Answer

B

Question 3

Why does a spinal need 2 to 3 mL while an epidural needs 15 to 20 mL for the same dermatomes?

Accepted Answer

Because of where the drug is placed relative to the nerve roots.

In spinal anaesthesia the drug enters cerebrospinal fluid, which directly bathes the nerve roots and the surface of the cord. There is no diffusion barrier at all, so a very small dose reaches an effective concentration at the target within minutes.

In epidural anaesthesia the drug is deposited outside the dura, in a space containing fat, lymphatics and veins. It must diffuse across the dura and arachnoid to reach the roots, and much of it is absorbed into the epidural venous plexus or taken up by fat before it gets there.

Every other difference follows. The epidural is slower in onset, less dense and more prone to patchy failure, spreads segmentally from the injection point rather than filling everything below a level, and carries a real risk of systemic toxicity because the dose is large and the veins are close.

The compensating advantage is the catheter, which allows the block to be topped up, extended and prolonged for days.

Question 4

A woman has a severe postural headache two days after an epidural for labour. Explain the mechanism and the definitive treatment.

Accepted Answer

Post-dural puncture headache following inadvertent dural puncture by the Tuohy needle.

Cerebrospinal fluid leaks through the dural hole faster than it is produced. Intracranial pressure falls, the brain loses its fluid cushion and sags, and traction on pain-sensitive meninges and vessels produces the headache, with compensatory cerebral vasodilatation contributing.

Every feature follows from that. The headache is postural because the sag is gravity dependent, so it is worse sitting or standing and relieved lying flat. Neck stiffness, photophobia and tinnitus accompany it, and traction on the sixth cranial nerve can cause diplopia. Onset is typically 24 to 48 hours later rather than immediate.

The large bore of the epidural needle explains the severity, with incidence reaching 30 to 40 per cent after such a puncture compared with under 2 per cent for a fine pencil-point spinal needle.

The definitive treatment is an epidural blood patch: 15 to 20 mL of the patient's own blood injected at or below the level of the puncture, which clots to seal the leak and raises epidural pressure. Relief is often immediate.

Question 5

Which brachial plexus approach is used for shoulder surgery, and what complication is almost universal with it?

Accepted Answer

The interscalene approach, which blocks the plexus at the level of the roots and trunks in the interscalene groove and reliably covers the shoulder and proximal arm.

Ipsilateral hemidiaphragmatic paresis occurs in a very high proportion of cases, because local anaesthetic spreads anteriorly to the phrenic nerve as it lies on the anterior scalene muscle. It is therefore avoided in significant respiratory disease and in contralateral phrenic palsy.

The approach also spares the lower trunk frequently, so the ulnar distribution may be missed, which is one reason it is unsuited to hand surgery.

For contrast, the supraclavicular approach gives the most complete arm block but risks pneumothorax, the infraclavicular approach is deeper with a risk of vascular puncture, and the axillary approach frequently spares the musculocutaneous nerve, which leaves the lateral forearm unblocked.

Question 6

Ten minutes after a supraclavicular block a patient reports a metallic taste and tinnitus, then convulses. Give the management sequence.

Accepted Answer

Local anaesthetic systemic toxicity, from vascular absorption or an unrecognised intravascular injection.

The prodrome is characteristic and follows the concentration: perioral tingling and metallic taste, then tinnitus and visual disturbance, then agitation and muscle twitching, then convulsions.

Stop injecting immediately and call for help.

Secure the airway and give 100 per cent oxygen, since hypoxia and acidosis both substantially worsen toxicity by increasing the free unbound drug fraction and impairing myocardial function.

Control the seizure with a benzodiazepine rather than propofol, because propofol contains far too little lipid to be therapeutic and adds cardiovascular depression.

Give 20 per cent lipid emulsion: a bolus of 1.5 mL/kg over two to three minutes, or 100 mL if over 70 kg, followed by an infusion, repeated or doubled if the response is inadequate, to an upper limit of about 12 mL/kg. The proposed mechanism is a lipid sink partitioning drug out of cardiac tissue plus a direct metabolic effect.

If cardiac arrest occurs, reduce adrenaline doses, avoid vasopressin, and continue for a prolonged period, since bupivacaine dissociates slowly from cardiac sodium channels.

Question 7

A patient for hip surgery received prophylactic enoxaparin at 10 pm and is listed at 8 am. Can a spinal be performed, and what follows?

Accepted Answer

Not at 8 am. Only ten hours will have elapsed, and the required interval after a prophylactic dose of low molecular weight heparin is twelve hours, so the block is delayed until 10 am.

The interval exists to prevent vertebral canal haematoma. The epidural space contains a rich venous plexus, and puncturing it while the anticoagulant is still active risks bleeding into a rigid space with no room to expand.

The consequence is severe. Presentation is back pain with progressive neurological deficit, and decompression is needed ideally within about eight hours, because delay converts a recoverable deficit into permanent paraplegia.

The next enoxaparin dose is withheld until at least four hours after the block. If a catheter is placed, removal obeys the same intervals as insertion, since withdrawal can traumatise a vein exactly as insertion can. This is the point most often missed.

For therapeutic rather than prophylactic dosing the interval is 24 hours. Postoperatively, regular neurological observation is mandatory, and any deficit deeper or longer-lasting than the expected block is imaged urgently by magnetic resonance rather than observed.

Question 8

Five minutes after a spinal for caesarean section a patient becomes bradycardic and hypotensive, then reports tingling hands and difficulty breathing. What is happening and what is done?

Accepted Answer

A developing total spinal, meaning the block is ascending far above the intended level.

Each sign localises the level. Tingling in the hands indicates a block reaching C8 to T1. Difficulty breathing indicates intercostal paralysis, with the diaphragm still working through C3 to C5, so the patient can breathe but feels unable to. Bradycardia confirms blockade above T4, where the cardiac accelerator fibres arise, so the compensatory tachycardia is abolished.

If it continues, phrenic involvement produces apnoea and brainstem hypoperfusion produces loss of consciousness.

Management is anticipatory and entirely supportive. Give 100 per cent oxygen and prepare to intubate and ventilate. Give fluids and a vasopressor, phenylephrine being preferred in obstetrics. Treat bradycardia with atropine. Ensure left uterine displacement, since aortocaval compression is compounding the hypotension.

Do not tilt head-down with a hyperbaric solution, which would drive the block higher.

And sedate the patient once ventilation is established, since a conscious paralysed patient being ventilated is experiencing awareness under paralysis. The block then recedes with time; there is no antidote.

Practice — "Regional & Spinal Anesthesia"

Sign in to save attempts to your dashboard and track your accuracy over time

Find a verified tutor

Join a live course

Browse coaching centres

About

Categories

Support

Documentation

Get Study Tips & Updates

Download Our App

Download for iOS

Download for Android

Popular Cities