Question 1

What does a positive diagnostic block tell you?

Accepted Answer

If pain settles after local anaesthetic is placed accurately into a suspected structure, that structure is likely to be contributing to the pain. A positive block supports rather than proves the diagnosis, because the anaesthetic can spread to nearby structures, a placebo effect can occur, pain can be referred from elsewhere, and an incomplete block can mislead.

Question 2

What is the difference between lidocaine and bupivacaine?

Accepted Answer

Both are amide local anaesthetics, but they differ in timing. Lidocaine has a fast onset and a short duration, which suits an immediate diagnostic test. Bupivacaine has a slower onset and a longer duration. The UK adult maximum single dose is 200 mg for plain lidocaine and 150 mg for bupivacaine.

Question 3

What is local anaesthetic systemic toxicity?

Accepted Answer

It is a dangerous reaction to too high a concentration of local anaesthetic in the blood, usually from injecting into a vessel or exceeding the maximum dose. It often progresses from numbness around the mouth, a metallic taste, ringing in the ears and agitation to seizures and cardiovascular collapse, but it can present suddenly or some time after the injection.

Question 4

How is local anaesthetic systemic toxicity treated?

Accepted Answer

Stop injecting and call for help. Maintain the airway, give 100% oxygen and control seizures. The specific treatment is intravenous 20% lipid emulsion, a 1.5 mL/kg bolus over 2 to 3 minutes followed by an infusion. If the heart stops, give CPR by standard protocols with a smaller adrenaline dose (1 microgram/kg rather than 1 mg) and avoid vasopressin. Recovery may take over 1 hour, propofol is not a substitute for lipid, and lidocaine is not used as an anti-arrhythmic.

Local Anaesthetic and Diagnostic Blocks

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