Local anaesthetics: adjuvants: practice question

A Anaesthesia question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Anaesthesia · Local anaesthetics: adjuvants

Sample item

Why is adrenaline added to lignocaine for infiltration, and in which site must the combination be avoided?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. It causes local vasoconstriction, prolonging the block and reducing systemic absorption; avoid in the fingers, toes, penis and ear because of ischaemia of end arteries

Adrenaline causes vasoconstriction at the injection site, which delays absorption of the local anaesthetic, prolongs its duration, lowers peak plasma levels (so the maximum safe dose rises, from 4.5 to 7 mg/kg for lignocaine) and reduces bleeding. It must not be used for ring blocks of the digits, penile blocks or other end-artery territories because of the risk of ischaemic necrosis, and it should be used with caution in patients with severe cardiovascular disease.

Option by option

  • A. It increases the speed of absorption, shortening the block; avoid in the thigh

    Adrenaline slows absorption, and does not shorten the block.

  • B. It converts lignocaine to an ester, so it is avoided in the abdomen

    Lignocaine is an amide, and adrenaline does not change its class.

  • C. It acts as a muscle relaxant; avoid in the face

    Adrenaline has no muscle-relaxing action.

  • D. It causes local vasoconstriction, prolonging the block and reducing systemic absorption; avoid in the fingers, toes, penis and ear because of ischaemia of end arteries (correct)

    Correct. Vasoconstriction prolongs the block, but end-artery areas are at risk of ischaemia.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Anaesthesia question

What is the answer to this Anaesthesia question?

The best answer is D, It causes local vasoconstriction, prolonging the block and reducing systemic absorption; avoid in the fingers, toes, penis and ear because of ischaemia of end arteries. Adrenaline causes vasoconstriction at the injection site, which delays absorption of the local anaesthetic, prolongs its duration, lowers peak plasma levels (so the maximum safe dose rises, from 4.

Why is "It increases the speed of absorption, shortening the block; avoid in…" not the answer?

Adrenaline slows absorption, and does not shorten the block.

Why is "It converts lignocaine to an ester, so it is avoided in the abdomen" not the answer?

Lignocaine is an amide, and adrenaline does not change its class.

Why is "It acts as a muscle relaxant; avoid in the face" not the answer?

Adrenaline has no muscle-relaxing action.

What concept does this question test?

It tests Local anaesthetics: adjuvants in Anaesthesia. 5 to 7 mg/kg for lignocaine) and reduces bleeding. It must not be used for ring blocks of the digits, penile blocks or other end-artery territories because of the risk of ischaemic necrosis, and it should be used with caution in patients with severe cardiovascular disease.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Local anaesthetics: adjuvants?

Make a table of each agent, its key advantage and its main side effect. Then use the flashcards and the other Anaesthesia questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.