Intravenous regional anaesthesia (Bier block) is planned for closed reduction of a distal radius fracture. Which agent is classically preferred, and what is the critical safety rule regarding tourniquet deflation?
- A Prilocaine, keep the cuff inflated for at least 20 minutes before deflation ✓
- B Bupivacaine, deflate after 45 minutes
- C Ropivacaine, deflate immediately once the block is surgical
- D Lidocaine, deflate in stages over 30 seconds regardless of elapsed time
Correct answer: A. Prilocaine, keep the cuff inflated for at least 20 minutes before deflation
Explanation
Prilocaine 0.5% is the agent of choice for the Bier block because it has the widest therapeutic index among amides and low toxicity on cuff release. The tourniquet must remain inflated for a minimum of 20 minutes so that tissue binding of the drug reduces the peak plasma bolus on deflation; earlier release risks systemic toxicity including methaemoglobinaemia with prilocaine. Bupivacaine is contraindicated for intravenous regional anaesthesia because of fatal cardiac arrhythmias reported on accidental early cuff release.
Reference: Miller's Anesthesia, 9th ed.
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