Tourniquets

Intraoperative tourniquets:

• Are used in extremity surgery to improve operating conditions
  Provide a (mostly) bloodless surgical field (bleeding may still occur from intramedullary vessels).
• May be contraindicated in peripheral vascular disease
• Should be inflated above the limb occlusion pressure
  • Determined by inflating the tourniquet and monitoring arterial flow with doppler
    Typically higher than SBP as tourniquet pressure is not transmitted evenly to deeper structures.
  • A safety margin of 40-80mmHg should then be added
• Should generally not be used for longer than 1.5-2 hours in a healthy adult
  ATP stores are exhausted after this point.
  • Tourniquet can be released for 10-15 minutes to allow ischaemic washout and reoxygenation prior to re-exsanguination and re-inflation

Local Effects of Tourniquets

Include:

• Muscle
  • Ischaemia
    Necrosis may occur after 2 hours
  • Post-tourniquet syndrome
    Swollen, pale, stiff, and weak limb for 1-6 hours after tourniquet application.
    • May lead to compartment syndrome
• Nerve
  
  • Temporary neuropathy
    Conduction block develops after 15-45 minutes.
  • Permanent neuropathy
    Exceedingly rare. Most neurological complications resolve within 6 months.
    • Pressure used is more significant than tourniquet time
• Vascular injury
  Permanent vascular injury is rare but catastrophic, and probably involves tourniquet pressure rupturing atheromatous plaque.

Systemic Effects of Tourniquets

Include:

• CVS
  • ↑ effective circulating volume following limb drainage and tourniquet inflation
    Bilateral thigh tourniquets may ↑ effective volume by 15%.
    • May lead to cardiac failure
  • Hypertension
    Gradual ↑ in BP seen with tourniquet use.
    • Probably due to tourniquet pain
• Pain
  Tourniquet inflation leads to a dull aching pain. This pain:
  • May occur despite apparently adequate neuraxial anaesthesia
    As the neuraxial block wears off, C-fibres will conduct dull pain though the patient remains insensate to sharp pain (due to ongoing A-fibre blockade).
  • Responds to 0.1-0.25mg/kg IV ketamine
    Beware treating as it will resolve with tourniquet deflation.
• Extremity
  • Temperature
    ↑ core temperature due to reduced heat loss from ischaemic limb, typically 0.5°C after 2 hours.

Effects of Tourniquet Deflation

Include:

• CVS
  • CVS instability
    Seen on tourniquet deflation, due to reactive hyperaemia and wash-out of anaerobic metabolites.
• Respiratory
  • ↑ PaCO₂
    Occurs on tourniquet deflation, may result in hyperventilation or hypercarbia (with subsequent changes to CNS blood flow).
• Extremity
  ↓ core temperature on tourniquet deflation due to heat redistribution.
• Fluid and Electrolyte
  • Hyperlactataemia
    On tourniquet deflation.
  • Hyperkalaemia
    On tourniquet deflation.
• Haematological
  • ↑ fibrinolysis

Reducing Tourniquet Risk

Key interventions to reduce iatrogenic harm include:

• Minimising pressure
• Minimising time
  Ensure alarms set.
• Padding under tourniquet
• Use a wider tourniquet
  Reduce pressure at any given point.
• 5-10 minute break for limb re-perfusion every 2 hours

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References

1. Deloughry JL, Griffiths R. Arterial tourniquets. Continuing Education in Anaesthesia Critical Care & Pain, Volume 9, Issue 2, 1 April 2009, Pages 56–60.