Local anaesthetics: dosing: 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: dosing

Sample item

What is the approximate maximum volume of 1% plain lignocaine that can be given by infiltration to a 70 kg adult, using a safe dose of 4.5 mg/kg?

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

The answer and the reasoning

B. About 31 mL

A 1% solution contains 10 mg/mL. The maximum dose of plain lignocaine is 4.5 mg/kg, so for 70 kg the maximum is 315 mg, which is 31.5 mL of 1% solution. With adrenaline, up to 7 mg/kg is permitted. Doses should be calculated before the block, and intravenous lipid emulsion should be available to treat toxicity.

Option by option

  • A. About 15 mL

    This would correspond to a 2% solution, which gives 15.75 mL, not a 1% solution.

  • B. About 31 mL (correct)

    Correct. 315 mg divided by 10 mg/mL gives 31.5 mL.

  • C. About 63 mL

    This would exceed the safe maximum dose by about double.

  • D. About 7 mL

    This is far below the maximum and arises from a calculation error.

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 B, About 31 mL. A 1% solution contains 10 mg/mL.

Why is "About 15 mL" not the answer?

This would correspond to a 2% solution, which gives 15.75 mL, not a 1% solution.

Why is "About 63 mL" not the answer?

This would exceed the safe maximum dose by about double.

Why is "About 7 mL" not the answer?

This is far below the maximum and arises from a calculation error.

What concept does this question test?

It tests Local anaesthetics: dosing in Anaesthesia. The maximum dose of plain lignocaine is 4.5 mg/kg, so for 70 kg the maximum is 315 mg, which is 31.5 mL of 1% solution. With adrenaline, up to 7 mg/kg is permitted. Doses should be calculated before the block, and intravenous lipid emulsion should be available to treat toxicity.

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: dosing?

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.