Question

Anaesthetic agents with vasoconstrictor properties are contraindicated in?

• A. Finger block
• B. Spinal block
• C. Epidural block
• D. Surface anaesthesia for bronchoscopy

Hint:

Think of regions supplied by end arteries with no collateral flow.

Answer 1

The Correct Option is A

Start from the purpose of the additive. A vasoconstrictor such as adrenaline shrinks local vessels to keep the anaesthetic where it is injected, lengthen its action and curb bleeding. The flip side is reduced blood supply to the injected region, which only becomes dangerous when that region has no alternative route of perfusion.

Now map this onto anatomy. Fingers and toes are perfused by terminal end arteries with negligible collateral circulation. If you constrict those vessels during a digital block, the digit can become critically ischaemic and even progress to gangrene. For this reason the classic teaching is to avoid adrenaline in ring blocks of the fingers, and likewise in the toes, nose tip, ear lobe and penis.

By contrast, a spinal or epidural injection acts on a richly perfused neuraxial region, and topical anaesthesia for bronchoscopy is applied to airway mucosa, neither of which depends on a single vulnerable end artery. So the end-artery ischaemia objection does not apply to them.

The block that must avoid vasoconstrictors is therefore the digital one.
\[\boxed{\text{Finger block}}\]