Tourniquet Use in Orthopaedic Surgery

What it is. The pneumatic tourniquet is one of the most common pieces of equipment in orthopaedic theatres: an inflatable cuff placed around the proximal limb and pumped above arterial pressure to stop blood flow, giving the surgeon a clean, bloodless field. It is used routinely for knee replacement, foot and ankle work, hand surgery and many trauma cases.

The trade. The benefit is better visibility and usually a faster operation with less blood in the wound. The cost is that the limb beyond the cuff is ischaemic for the duration, and the tissue under the cuff is squeezed hard. Almost every problem with tourniquets comes back to the two things the examiner will test, how much pressure and how long: get those right and apply the cuff properly and the device is very safe; get them wrong and you can injure nerves, muscle and skin.

Why it turns up in the viva. It links anatomy, physiology and safe practice in one device, so it is a favourite of basic-science and operative vivas alike. In knee replacement, whether to use it, for how long and at what pressure is an active debate you should be able to argue. In hand, foot and trauma surgery, cuff choice, exsanguination and time-keeping are everyday skills, and the reperfusion changes on deflation are a classic anaesthesia and physiology teaching point.

How to set a safe pressure, how to apply the cuff, when to avoid it and what can go wrong is the practical core examiners probe. It all reduces to one idea: the lowest effective pressure, the widest cuff, for the shortest time.

The device. A pneumatic tourniquet is an inflatable cuff connected to a console that pumps it to a set pressure and holds it there. When cuff pressure rises above the pressure in the limb's arteries, arterial inflow stops; the cuff also compresses the veins, so blood cannot drain in or out, and the limb beyond the cuff becomes pale and bloodless.

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Occlude at the lowest safe pressure. You need only enough pressure to stop arterial flow in that particular limb, and two factors decide how much that is:

• The patient's arterial pressure. A hypertensive patient needs more, which is why cuff pressure is linked to systolic blood pressure or to a measured occlusion pressure.
• The cuff and the limb. A wider cuff transmits pressure more efficiently and occludes flow at a lower set pressure. A large, conical or muscular limb needs more pressure than a thin one.

Limb occlusion pressure (LOP) is the minimum cuff pressure that stops arterial flow in that specific limb at that moment, detected by loss of a distal pulse or of a Doppler or plethysmography signal. Setting the cuff to LOP plus a safety margin gives a personalised pressure lower than the old fixed numbers, and lower pressure is safer for nerves and muscle.

A safe tourniquet is as much about technique as about the machine. Four steps make a reliable viva structure:

1. Choose and position the cuff. Use the widest cuff that fits and place it on the proximal limb, the upper arm or proximal thigh, where muscle bulk cushions the nerves. A contoured cuff fits a conical thigh better than a straight one.
2. Protect the skin. Apply padding or a limb-protection sleeve under the cuff, with no wrinkles, and keep skin-prep fluid from pooling beneath it.
3. Exsanguinate, then inflate. Elevate the limb for a few minutes, then apply an Esmarch bandage or limb roller from distal to proximal; where squeezing must be avoided, for example with suspected infection or tumour, elevate only. Then inflate to the set pressure and start the clock.
4. Record and monitor. Document the inflation pressure and start time, watch the total tourniquet time and keep the team aware of it, and warn the anaesthetist before deflation. Deflate and let the limb reperfuse before closing if needed.

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How long is safe. While the cuff is up, the limb beyond it has no blood supply. Tissue tolerates this for a while, because muscle and nerve can survive a period of ischaemia, but the margin shrinks with time. There is no single universally agreed maximum, but a widely used practical approach is to keep inflation as short as possible and to plan a deflation by about 2 hours. If more time is needed, the cuff is let down for a reperfusion break (commonly around 10 to 15 minutes) before re-inflating.

During inflation. The limb becomes ischaemic, acidotic and cold, and anaerobic metabolites (lactate, potassium, carbon dioxide) build up. Nerve and muscle function progressively fail, which underlies the temporary "tourniquet palsy" seen after long inflations.

At deflation. The pooled metabolites wash into the central circulation, causing a transient fall in blood pressure, a rise in end-tidal CO2, and rises in serum potassium and lactate. Blood also surges into the dilated limb, so central volume and pressure drop briefly. This is usually well tolerated in a fit patient but can be significant after a long inflation or in a frail or cardiac patient, which is exactly why you warn the anaesthetist first.

There are few absolute contraindications, but several situations where you should think hard, choose elevation-only exsanguination, or avoid the tourniquet altogether:

• Severe peripheral arterial disease. A tourniquet can damage diseased, calcified vessels and worsen distal ischaemia. A previous vascular bypass graft in the limb is a strong reason to avoid the cuff.
• Sickle cell disease or trait. The stagnant, hypoxic, acidotic limb beyond the cuff promotes sickling. Many avoid tourniquets here; if one is used, careful exsanguination, oxygenation and minimal time are advised.
• Limb infection. Exsanguinating an infected limb risks pushing organisms into the circulation; elevation-only exsanguination is preferred if a tourniquet is needed at all.
• Limb tumour. There is a theoretical risk of squeezing tumour cells into the circulation during exsanguination, so avoid the Esmarch and use gentle elevation, or avoid the tourniquet.

Other cautions include significant venous thromboembolism risk, severe crush or vascular injury in the same limb, and very poor skin condition under the cuff.

Easy to miss. Two more are worth naming explicitly, because they are easy to miss on a ward round and awkward to explain afterwards:

• Dialysis access in that arm. An arteriovenous fistula or graft must not have a cuff inflated over or above it, because thrombosis of the access can cost the patient their dialysis route. Check both arms before you position, and mark the limb.
• Known or suspected deep vein thrombosis in the limb. Exsanguination mechanically empties the deep veins and can dislodge established clot; if a tourniquet is unavoidable, exsanguinate by elevation alone and never with an Esmarch.

Beyond the bloodless field, the tourniquet is the safety device in a Bier block (intravenous regional anaesthesia, IVRA), a technique for short distal-limb procedures, typically under about an hour: hand or forearm surgery and fracture manipulation, for example.

Technique. Step by step:

1. Insert a cannula distally in the operative limb.
2. Exsanguinate: elevate, then apply an Esmarch.
3. Inflate a double-cuff tourniquet, proximal cuff first.
4. Inject dilute local anaesthetic into the distal vein, so that it fills the venous system and anaesthetises the limb.
5. When the proximal cuff becomes painful, inflate the distal cuff over the now-anaesthetised skin and release the proximal one.

The drug. Prilocaine is preferred for its low cardiotoxicity. Bupivacaine is contraindicated, being too cardiotoxic for this technique.

The danger is the cuff. The tourniquet is the only thing keeping the local anaesthetic in the limb. Premature deflation or cuff failure releases a bolus of local anaesthetic into the systemic circulation, causing local anaesthetic systemic toxicity (LAST): seizures and cardiovascular collapse.

Distinct from the theatre pneumatic cuff is the pre-hospital / trauma haemorrhage-control tourniquet, used for life-threatening external limb bleeding. This is the catastrophic haemorrhage ("C") that is addressed before the airway in the trauma primary survey.

Device and application. A windlass tourniquet (for example a Combat Application Tourniquet, CAT) or a pneumatic or improvised one is applied proximal to the wound and tightened until external bleeding stops and the distal pulse is abolished. If one does not control the bleeding, apply a second tourniquet side by side.

Principles. Apply it early for exsanguinating limb haemorrhage, record the time of application, mark it clearly and hand it over explicitly. Do not periodically release it in the field, because this rebleeds and disrupts the clot. The limb tolerates ischaemia for up to about 2 hours, after which the same reperfusion and metabolic load applies on release.

Conversion. In hospital, once the patient is resuscitated and bleeding is controlled, the tourniquet is converted to definitive haemostasis by direct repair or a haemostatic dressing.

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Nerve injury. This is the commonest serious complication and the one examiners chase. The crucial concept is that it is mainly mechanical, not ischaemic: the nerve is crushed under the cuff, so injury is worst at the edge of the cuff. Risk climbs with high pressure, long inflation time, a narrow cuff and a thin limb.

Which nerves, and the outlook. The vulnerable nerves are the radial nerve in the arm and the sciatic and common peroneal nerves in the lower limb. Most injuries are a neurapraxia that recovers over weeks to months, but severe or prolonged compression can cause lasting deficit. Prevention is the same theme throughout: lowest effective pressure, widest cuff, shortest time.

Post-tourniquet syndrome. After deflation the limb can become swollen, stiff, pale, weak and numb without an actual nerve transection. It reflects reperfusion oedema and ischaemic soft-tissue injury and is more likely after long or high-pressure inflations. It is usually self-limiting over days to weeks and is managed supportively, with elevation and time.

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Other harms. Five more complete the list.

• Skin injury: chemical burns and blisters from prep fluid pooling under the cuff, or from pressure on the skin
• Reperfusion and metabolic effects at deflation, described above
• Venous thromboembolism: venous stasis distal to the cuff can promote deep vein thrombosis, and there is a higher DVT signal with tourniquet use in knee replacement
• Muscle injury: crush plus ischaemia, worse with high pressure and long time; rhabdomyolysis is rare, after very prolonged or high-pressure inflation
• Equipment failure: a wrong pressure or a leak, so check the system before use

• Lowest effective pressure is the consistent message across modern guidance (for example AORN perioperative recommendations and AAOS/specialty education): set cuff pressure from limb occlusion pressure plus a margin and use the widest cuff that fits, rather than a fixed high pressure for everyone.
• Documentation of cuff pressure and total tourniquet time in the operative record is standard safe-surgery practice worldwide.

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• Knee replacement practice varies globally: some surgeons use a tourniquet for the whole case, some only for cementation, and some omit it entirely. The trend, supported by meta-analyses, is toward shorter and lower-pressure use because of the early pain, slower recovery, and higher deep vein thrombosis signal seen with full-length high-pressure inflation.
• Special populations (sickle cell disease, severe peripheral arterial disease, previous vascular bypass, limb infection or tumour) are handled cautiously everywhere, with elevation-only exsanguination or avoidance of the tourniquet depending on the situation.

Total knee arthroplasty is where tourniquet use has been studied most, because surgeons disagree about whether the bloodless field is worth the soft-tissue cost.