Tourniquet physiology and complications

Surgical approach

• Applied to proximal limb (arm/thigh) to provide a bloodless field for limb surgery (e.g. hand surgery, arthroscopy, ORIF, tendon repair).
• Limb is elevated and often exsanguinated (e.g. Esmarch bandage) before cuff inflation.
  • Avoid exsanguination if infection, malignancy, fresh fracture, or DVT risk is a concern (local policy varies).
• Cuff inflated to a pressure above limb occlusion pressure (LOP) to stop arterial inflow; surgery proceeds; cuff deflated at end (sometimes with intermittent reperfusion if prolonged).
• May use single or dual cuffs (e.g. Bier’s block uses double cuff to reduce tourniquet pain).

Anaesthetic management (overview)

• Type of anaesthesia: GA or regional (brachial plexus block; spinal/epidural; IVRA for distal upper limb).
• Airway: often SGA for short peripheral surgery; ETT if long case, aspiration risk, prone/lateral, significant comorbidity, or need for controlled ventilation.
• Duration: aim to keep continuous inflation time as short as possible; many departments use thresholds around 60–90 min (upper limb) and 90–120 min (lower limb) before considering reperfusion breaks (local policy).
  • If prolonged inflation anticipated: discuss staged deflation/reinflation plan with surgeon; document times clearly.
• How painful: tourniquet pain is common with inflation >30–45 min, especially under light GA or incomplete regional block.
  • Analgesia plan: deepen anaesthesia, opioids, ketamine, alpha-2 agonist, magnesium; ensure block adequacy; consider additional peripheral nerve block or local infiltration.
• Monitoring: standard ASA; consider invasive BP for major comorbidity or expected large haemodynamic swings at inflation/deflation; temperature monitoring for long cases.
• Key anaesthetic risks to anticipate: haemodynamic changes at inflation/deflation, metabolic load on deflation, nerve/skin injury, DVT/PE risk, and (rare) local anaesthetic toxicity if IVRA.

Principles and definitions

• Tourniquet = circumferential cuff inflated to occlude arterial inflow (and venous outflow) to a limb.
• Limb occlusion pressure (LOP) = minimum cuff pressure required to stop arterial flow (varies with limb size, cuff width, BP, tissue composition).
  • Wider cuffs achieve occlusion at lower pressures; narrow cuffs require higher pressures and increase risk of nerve/skin injury.
• Typical inflation pressures (institution-dependent): upper limb often ~200–250 mmHg; lower limb often ~250–350 mmHg, or LOP + safety margin.
  • Avoid “one pressure fits all”; consider LOP-based systems where available.

Physiological effects: during inflation

• Haemodynamics: transient increase in SVR and MAP at inflation (pain/sympathetic response), more marked if awake/light anaesthesia.
  • May see tachycardia and hypertension; treat with analgesia, deepening anaesthesia, beta-blocker/vasodilator if needed.
• Tourniquet pain: dull, poorly localised pain despite adequate surgical anaesthesia; typically begins after 30–45 min.
  • Mechanisms: C-fibre activation, ischaemia, nerve compression, central sensitisation; not fully blocked by A-delta blockade alone.
• Respiratory/ventilation: under GA, may see gradual rise in EtCO2 during prolonged inflation due to reduced CO2 washout from the isolated limb (and changes in ventilation/CO2 production).
• Thermoregulation: reduced heat loss from isolated limb; overall effect usually small but relevant in long cases/children.

Local limb physiology: ischaemia and reperfusion

• Ischaemia: anaerobic metabolism distal to cuff → lactate accumulation, acidosis, hyperkalaemia, myoglobin release (if severe/prolonged).
• Reperfusion on deflation: washout of metabolites into systemic circulation → fall in SVR/MAP, rise in EtCO2, transient metabolic acidosis, and potential dysrhythmias.
  • Magnitude depends on limb mass (thigh > arm), duration of inflation, baseline cardiorespiratory reserve, and intravascular volume status.
• Inflammation/oxidative stress: reperfusion generates reactive oxygen species and inflammatory mediators; clinical relevance greatest in prolonged ischaemia or vulnerable patients.

Systemic effects: during deflation (what to expect on monitors)

• Blood pressure: drop in MAP (often within 1–3 min) due to reduced SVR and relative hypovolaemia from limb reperfusion.
  • Treat: increase FiO2, ensure adequate ventilation, fluid bolus if appropriate, vasopressor (metaraminol/phenylephrine/ephedrine) guided by HR and physiology.
• EtCO2: rises as CO2-rich blood returns; may require increased minute ventilation.
• ECG: risk of bradycardia/ectopy (rarely VF) in susceptible patients, especially with significant hyperkalaemia/acidosis or underlying cardiac disease.
• Temperature: slight fall possible due to reperfusion of cooler limb.

Complications (local)

• Nerve injury (neuropraxia most common): due to pressure, shear, ischaemia; risk increases with high cuff pressure, narrow cuff, prolonged time, and poor padding/positioning.
  • Common nerves: radial/ulnar/median (upper limb), common peroneal (lower limb).
• Skin/soft tissue injury: pressure necrosis, blistering, chemical burns (prep solution trapped under cuff), friction burns.
  • Prevention: adequate padding, avoid pooling of alcoholic prep under cuff, correct cuff size and placement, avoid wrinkles.
• Compartment syndrome: rare; can occur after reperfusion, trauma, prolonged ischaemia, or tight dressings/casts; pain out of proportion, pain on passive stretch, tense compartments.
• Vascular injury: arterial thrombosis/embolism, intimal damage; higher risk in peripheral vascular disease, diabetes, calcified vessels, sickle cell disease.
• Muscle injury/rhabdomyolysis: prolonged ischaemia, high pressures; may lead to myoglobinuria and AKI (rare in routine elective durations).

Complications (systemic)

• Hypotension at deflation: common; can be significant in hypovolaemia, neuraxial anaesthesia, or cardiac disease.
• Metabolic derangement: acidosis, hyperkalaemia, lactataemia; clinically important with long inflation times and large muscle mass (thigh).
• Dysrhythmias/cardiac arrest: rare; risk increased by severe hyperkalaemia, acidosis, hypothermia, and poor cardiac reserve.
• Thromboembolism: DVT/PE risk relates to surgery, immobility, and patient factors; tourniquet may contribute via venous stasis/endothelial injury (evidence mixed).
• Tourniquet-related hypertension during inflation (especially under regional/awake): treat pain/anxiety; consider clonidine/dexmedetomidine, opioid, or conversion to GA if uncontrolled.

Special situations

• Sickle cell disease/trait: avoid hypoxia, acidosis, hypothermia, dehydration; tourniquet use is controversial—if used, minimise time and ensure meticulous physiological optimisation and senior discussion.
• Peripheral vascular disease/AV fistula/previous vascular graft: increased risk of ischaemic and thrombotic complications; consider avoiding tourniquet or using lowest effective pressure/time.
• IVRA (Bier’s block): ensure correct cuff function, minimum inflation time before deflation (commonly ≥20 min), incremental deflation technique per protocol to reduce LAST risk.
• Children: smaller limbs and lower LOP; higher risk of pressure injury if adult pressures used—use paediatric cuffs and LOP-based settings.

Prevention and practical points

• Before inflation: check cuff size/position, padding, skin integrity; document baseline neurovascular status if relevant; record inflation time and pressure.
• Pressure strategy: use LOP + safety margin where possible; otherwise use lowest pressure that maintains a bloodless field.
• Time strategy: avoid prolonged continuous inflation; if extended surgery, consider planned reperfusion breaks (e.g. 10–15 min) with surgeon agreement (local policy).
• Analgesia: anticipate tourniquet pain; ensure adequate regional block coverage; consider adjuncts (ketamine, clonidine/dexmedetomidine) and multimodal analgesia.
• Deflation readiness: communicate before deflation; increase vigilance for hypotension/EtCO2 rise; consider pre-emptive fluid/vasopressor in high-risk patients.