On postoperative day 1 after a free anterolateral thigh flap transfer to the floor of mouth, the flap appears dusky purple and swollen. Needle prick with a 25-gauge needle produces brisk dark bleeding that brightens rapidly. What is the most likely diagnosis and correct action?

• A Arterial thrombosis, immediate return to theatre
• B Reperfusion oedema, observe with hourly checks
• C Venous congestion from venous thrombosis, immediate return to theatre ✓
• D Haematoma beneath the flap, apply pressure dressing

Explanation

Brisk dark venous bleeding from a prick test indicates blood is still entering the flap but cannot leave, so this is venous outflow obstruction. Venous compromise must be explored immediately because a congested flap can be lost within hours, whereas arterial thrombosis gives a pale flap with absent or scanty bleeding on prick testing. Observation or compression wastes the narrow salvage window.

Reference: Grabb and Smith's Plastic Surgery, 8th ed.

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