Answer:
Leeches are worms that feed on blood from a mammalian host. While the first uses of leeches for medicinal purposes date back 3500 years, their modern use in flap surgery dates from 1960 while their use in digital replantation dates from 1981. Incidentally, the term leech derives from the Old English word for physician.
The species most commonly used is Hirudo medicinalis. Leeches are indicated for venous congestion which threatens a flap or digit. Survival for threatened pedicle flaps or replanted digits with leech application are currently 60-70%. Leeches have a front sucker which makes a 2-mm incision and can extract about 5-15 cc of blood over 30 minutes. Their primary benefit results from the injection of an anticoagulant, hirudin, present in leech saliva which can last for several hours after detachment permitting up to 50 cc of venous oozing. Hirudin inhibits thrombin, blocking the conversion of fibrinogen to fibrin and platelet aggregation response to thrombin. Poor leech sucking is considered a bad prognostic sign for flap survival and may indicate the presence of arterial insufficiency.
The leech is applied to a clean area of the flap with the head (narrow end) directed toward the area needing treatment. The skin may need to be pricked to produce a drop of blood in order to induce feeding. The leech will usually detach after 30 minutes. If an area stops oozing after leech detachment, it can be wiped with a heparin-soaked gauze to promote rebleeding. Leeches cannot be reused. After use they are placed in alcohol and disposed of with the biohazardous waste. They are applied about every 4 hours but the frequency should be tailored to the circumstances. In situations where no oozing is seen after leech detachment, they can be applied every 30 minutes.
Infection and low blood volume are the main complications of leech use. Within the leech gut is a gram-negative rod, Aeromonas hydrophilia, which can cause infections within 10 days after leech use. Infection rates of 0-20% have been reported. Empiric antibiotic therapy using an aminoglycoside or third-generation cephalosporin is advocated by some clinicians.