During intravenous regional anaesthesia (Bier block) for closed reduction of a forearm fracture, the tourniquet cuff has been inflated for only 8 minutes when the surgeon finishes and requests deflation. Why is early deflation dangerous, and what is the accepted minimum inflation time?

• A Early deflation triggers tourniquet pain; deflate no sooner than 60 minutes
• B Drug causes irreversible nerve injury if released early; deflate no sooner than 45 minutes
• C Early deflation causes rebound hyperaemia and bleeding; deflate no sooner than 30 minutes
• D Drug remains largely intravascular and unbound; deflate no sooner than 20 minutes ✓

Explanation

In a Bier block, local anaesthetic injected into an exsanguinated, occluded limb initially stays free in the venous system. With time it binds to tissue and diffuses out of the vascular compartment, so systemic levels after deflation fall sharply. Deflating before about 20 minutes releases a large bolus into the circulation and risks LAST with CNS excitation and arrhythmias. Prilocaine or lidocaine without preservative are the standard agents.

Reference: Miller's Anesthesia, 9th ed.

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Written and medically reviewed by the StethoPrep medical team.