Yes, the NHS Really Uses Leeches: Here Is Why

A patient has undergone reconstructive surgery and the flap looks increasingly dark, swollen and tense. The tissue is receiving blood, but it is not draining properly. For the flap to survive, arterial blood needs to reach the tissue and venous blood needs to be able to leave.

When venous drainage fails, blood collects within the tissue. Pressure rises, oxygen delivery becomes less effective and the flap can begin to fail. The surgical team may need to correct the problem urgently. In selected cases, however, a treatment that looks surprisingly old-fashioned can provide temporary drainage while the tissue establishes a better venous outflow: a medicinal leech.

Medicinal leech therapy has a small but established role in modern plastic and reconstructive surgery. To understand the treatment, start with the circulation through the reconstructed tissue.

When blood can get in but cannot get out

Imagine a free flap that has been moved from one part of the body to another. Its small blood vessels are reconnected so that arterial blood can enter and venous blood can leave. If arterial inflow fails, the tissue is not receiving enough oxygenated blood. If venous outflow fails, blood may still enter but cannot drain away effectively. This is venous congestion.

As congested blood accumulates, the flap may become dusky, blue or purple, swollen and tense. Capillary refill can become brisk because blood is already pooling within the tissue. Depending on the specialist assessment method, dark blood may be seen when the tissue is tested. These findings are interpreted alongside the wider flap assessment, which may include temperature, texture and Doppler assessment according to the procedure and local protocol.

Venous congestion is time-critical. Rising pressure within the microcirculation interferes with effective tissue perfusion and can contribute to thrombosis and tissue loss. A deteriorating flap therefore needs prompt specialist surgical assessment. Leech therapy is not a substitute for correcting a surgically reversible problem. It may be used when venous drainage cannot be restored immediately, further surgery is not feasible, or the specialist team needs a temporary way of reducing congestion while venous drainage develops.

How can a leech help?

Medicinal leeches are specially bred for clinical use. When placed on congested tissue, the leech attaches and removes a relatively small amount of blood. Blood removal is only part of the effect. The bite continues to bleed after the leech detaches.

Leech saliva contains biologically active substances that interfere with haemostasis and support continued local blood flow. Hirudin inhibits thrombin, while other salivary components reduce platelet activity and influence local vascular responses. Once the leech has finished feeding and detaches, the bite can continue to ooze for hours.

The ongoing bleeding allows congested venous blood to continue leaving through the bite site. As pressure falls, arterial inflow may be better able to continue delivering oxygenated blood to the flap.

The leech therefore does not repair the vein. It provides temporary venous drainage. Treatment may need to be repeated over several days while new venous connections develop or until the specialist team is satisfied that the tissue can maintain adequate circulation without it.

A leech commonly remains attached for around 15 to 60 minutes before detaching. The number used, how often they are applied and how long treatment continues are clinical decisions based on the flap, the response to treatment and the organisation's protocol.

What is the nurse watching?

As a student nurse, you are more likely to encounter leech therapy as part of caring for and monitoring the patient than to apply the leeches yourself. The observations are focused on whether the flap is improving or deteriorating.

Flap observations may include colour, warmth, swelling or texture, capillary refill, bleeding and a Doppler signal where this forms part of the monitoring plan. The exact observation schedule and technique depend on the surgery and local policy. The pattern over successive observations helps the team recognise whether the flap is improving or becoming more congested.

You may also see the nurse document when a leech is applied and when it detaches, observe the bite site and expected oozing, check dressings, monitor the patient's observations and pain, review prescribed antibiotics and follow blood results. Leeches need to remain contained at the intended treatment site and each leech is used for one patient only.

Students should work within their level of competence and supervision. Do not independently initiate, apply, remove or dispose of medicinal leeches unless this is permitted within the local procedure and you are appropriately supervised. An attached leech should not simply be pulled off or disturbed. Follow the specialist team's instructions and the organisation's policy.

If the flap becomes increasingly dusky, swollen or cool, capillary refill changes, the expected bleeding alters, pain increases, or there is any other sudden deterioration in the tissue or patient, escalate promptly rather than waiting for the next scheduled observation.

The treatment creates risks of its own

The bite is intended to continue bleeding after the leech detaches. With repeated treatment, however, the cumulative blood loss can become clinically significant.

Patients may therefore have regular blood tests, particularly haemoglobin and the wider full blood count, alongside clinical assessment of bleeding and haemodynamic observations. Some patients receiving prolonged treatment require blood transfusion. Excessive or uncontrolled bleeding, a falling haemoglobin or signs of haemodynamic compromise need clinical review.

There is also an important infection risk. Medicinal leeches are bred for medical use, but they are not sterile. Aeromonas species live naturally within the leech digestive system and can cause infection in the patient. Antibiotic prophylaxis is therefore commonly prescribed during leech therapy. The antibiotic and duration should follow local antimicrobial guidance and microbiology or specialist advice rather than being assumed from another organisation's protocol.

The patient may also find the treatment frightening or unpleasant. Seeing a live leech attached to reconstructed tissue is very different from hearing the treatment explained in theory. Consent, clear explanations, privacy and an opportunity to ask questions remain part of good nursing care. A patient who does not want to watch the treatment should not be made to feel that they need to.

Back to the congested flap

Return to the patient whose flap had become dark and swollen. While the leech is part of the treatment, the team is assessing the flap itself for signs of recovery or further deterioration.

As treatment continues, the team repeatedly reassesses the flap. Is the colour improving? Is swelling reducing? What has happened to capillary refill, temperature, texture and the Doppler signal? Is the bite continuing to bleed as expected? What is happening to the patient's haemoglobin and observations?

If the tissue continues to deteriorate, leeches cannot be treated as reassurance that something is being done. Persistent venous congestion can still lead to partial or complete flap failure and may require further surgery. Medicinal leech therapy can improve the chance of salvaging selected congested tissue, but it cannot guarantee survival.

The physiology brings the treatment together. Blood is entering tissue that cannot drain it effectively, so the leech provides a temporary route for some of that congested blood to leave. Meanwhile, the surgical team continues to assess the flap and determine whether adequate venous drainage is becoming established.

References

Hull University Teaching Hospitals NHS Trust (2025) Leech therapy. Available at: https://www.hey.nhs.uk/patient-leaflet/leech-therapy/.

Mousavian, A., Sabzevari, S., Parsazad, S., Moosavian, H. and Leili, E.K. (2022) ‘Leech therapy protects free flaps against venous congestion, thrombus formation, and ischemia/reperfusion injury: benefits, complications, and contradictions’, Archives of Bone and Joint Surgery, 10(4), pp. 252–260. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC9034796/.

Oxford University Hospitals NHS Foundation Trust (2024) Leech therapy. Available at: https://www.ouh.nhs.uk/media/syif1xee/78372therapy.pdf.

University Hospitals Sussex NHS Foundation Trust (2026) Leech therapy for a congested free flap. Available at: https://www.uhsussex.nhs.uk/resources/leech-therapy-for-a-congested-free-flap/.