Question
A 38-year-old healthcare worker accidentally injects epinephrine into his index finger while assisting in an allergic emergency. Shortly after, the digit becomes pale, cold, and cyanotic.
Which of the following is the most appropriate immediate management?
a. Oral amlodipine
b. Intravenous lipid emulsion
c. Topical nitroglycerin only
d. Local infiltration with an alpha-blocker
e. Intravenous prostacyclin
Answer
Local infiltration with an alpha-blocker (Phentolamine)
Detailed Explanation
This scenario describes accidental adrenaline (epinephrine) injection into a digit, leading to intense vasoconstriction via α₁-adrenergic receptor stimulation, causing digital ischaemia (cold, blue finger).
The key principle:
- Adrenaline → α-receptor stimulation → vasoconstriction
- Reversal requires α-blockade
Phentolamine is a non-selective α-adrenergic antagonist that directly counteracts this vasoconstriction.
- Given by local infiltration around the affected area
- Causes rapid vasodilation → restoration of blood flow
Why other options are wrong:
- Iloprost: systemic vasodilator (used in severe Raynaud’s), not first-line here
- Intralipid: for local anaesthetic toxicity, not adrenaline
- Nifedipine: oral, slow onset → not useful in acute digital ischaemia
- Sildenafil: systemic vasodilator, not appropriate for acute localized reversal
Cheat Sheet (Exam-Oriented)
Adrenaline accidental injection → Key facts
- Mechanism: α₁ vasoconstriction → digital ischaemia
- Clinical signs: cold, pale/blue finger, pain
- Emergency risk: tissue necrosis
Management
- First-line: local phentolamine infiltration
- Alternative (less effective): topical GTN
Drug Mechanism
- Phentolamine = α-blocker → reverses vasoconstriction
High-yield association
- “Adrenaline + digit + ischaemia → phentolamine”
Flashcards
Q1: What is the mechanism of digital ischaemia after adrenaline injection?
A: α₁-mediated vasoconstriction
Explanation: Adrenaline stimulates alpha receptors → reduced blood flow
Q2: What is the antidote for adrenaline-induced digital ischaemia?
A: Phentolamine
Explanation: It blocks alpha receptors and reverses vasoconstriction
Q3: Route of administration of phentolamine in this scenario?
A: Local infiltration
Explanation: Direct delivery ensures rapid reversal
Q4: Why is nifedipine not useful acutely?
A: Slow onset and systemic effect
Explanation: Not effective for urgent localized vasospasm
Q5: What complication occurs if untreated?
A: Digital necrosis
Explanation: Prolonged ischaemia leads to tissue death
MCQs (High Difficulty)
MCQ 1
A patient develops finger ischaemia after accidental epinephrine injection. Which receptor is primarily responsible?
a. β1
b. β2
c. α1
d. Dopamine D1
e. Muscarinic M3
Answer: c
Explanation: α1 receptors mediate vasoconstriction in peripheral vessels.
MCQ 2
Which of the following best describes the mechanism of action of phentolamine?
a. Selective β2 agonism
b. Non-selective α antagonism
c. Calcium channel blockade
d. Nitric oxide donation
e. PDE-5 inhibition
Answer: b
Explanation: Phentolamine blocks both α1 and α2 receptors.
MCQ 3
Which of the following is false regarding adrenaline-induced digital ischaemia?
a. It is due to vasoconstriction
b. It can lead to tissue necrosis
c. Oral vasodilators are first-line
d. Local treatment is preferred
e. It is a medical emergency
Answer: c
Explanation: Oral vasodilators are too slow; local phentolamine is first-line.
MCQ 4
Which drug is most appropriate if phentolamine is unavailable?
a. IV heparin
b. Topical glyceryl trinitrate
c. Oral sildenafil immediately
d. IV labetalol
e. Intramuscular atropine
Answer: b
Explanation: Topical GTN can provide some vasodilation if phentolamine unavailable.
MCQ 5
Which of the following scenarios most strongly indicates use of phentolamine?
a. Cocaine overdose with hypertension
b. Accidental epinephrine injection into finger
c. Anaphylaxis with hypotension
d. Stable angina
e. Chronic Raynaud’s disease
Answer: b
Explanation: Classic indication is reversal of local vasoconstriction from adrenaline.
Summary for Quick Exam Revision
Accidental digital injection of adrenaline leads to intense α₁-mediated vasoconstriction, producing a cold, pale, and cyanotic finger with risk of necrosis. The definitive and most effective treatment is immediate local infiltration of phentolamine, a non-selective alpha-adrenergic antagonist, which rapidly reverses vasospasm and restores perfusion. Systemic vasodilators like nifedipine or sildenafil are too slow and not appropriate for acute localized ischaemia, while intralipid is used for local anaesthetic toxicity and iloprost is reserved for severe Raynaud’s. The key exam trigger is “adrenaline + finger ischaemia,” which should instantly lead to “phentolamine infiltration.” Early intervention prevents permanent tissue damage, making this a time-sensitive emergency scenario.