Surgical Tourniquets

Types of Tourniquets

1. Pneumatic:
   • Automatic: More accurate.
   • Manual.
2. Non-Pneumatic:
   • E.g., for finger surgery.

Contra-indications to Tourniquet Use

1. Absolute:
   • Severe crush injuries.
   • Compartment syndrome.
2. Relative:
   • Sickle cell disease.
   • Peripheral vascular disease.

Nerve Injury Related to Tourniquet Use

• Cause: Direct compression neuropraxia at the edge of the cuff.
  • The central part of the cuff is spared.
• Mechanism:
  • Displacement of the node of Ranvier from its normal relation to the Schwann cell.
  • Causes stretching of the myelin sheath.
  • Not due to ischaemic injury to nerves.

Cuff Design and Pressures

• Pressures:
  • Highest at the center of the cuff where skin pressure is 95% of the cuff pressure.
  • Higher cuff pressure correlates to higher tissue pressure.
  • Tissue pressures fall as limb circumference increases.
  • Only a 2% decrease in pressure from the surface to the deepest tissues.
• Cuff Width:
  • Narrower cuffs require higher occlusion pressure for the same limb circumference.
  • Wider cuffs should be used in larger limbs to reduce the risk of neurological injury.

Limb Occlusion Pressures (LOP)

• Pressure required to occlude arterial flow distal to the cuff.
• Traditional Recommendations:
  • Add 50–75 mmHg to the systolic pressure for the upper limb.
  • Double the systolic pressure for the lower limb.
• More Accurate Method:
  1. Gradually increase tourniquet pressure until the distal pulse is lost.
  2. Adjust:
     • Add 40 mmHg for occlusion pressures <130 mmHg.
     • Add 60 mmHg for occlusion pressures <190 mmHg.
     • Add 80 mmHg for occlusion pressures >190 mmHg.
  • This method results in significantly lower tourniquet pressures.

Limb Exanguination

• More effective than elevation alone.
• Contraindications:
  • Infection.
  • Metastatic disease.
  • Venous thrombosis.

Limb Protection

• Studies show padding under the cuff reduces skin injuries.
• Two-layer elastic stockinette is superior to Velband padding.

Duration of Tourniquet Use

• Recommended: 2 hours (safe, especially in the upper limb).
• No definitive unsafe time, but:
  • Longer durations = increased risk of nerve injury and tissue ischaemia.
  • Up to 3 hours may be acceptable in the lower limb (use common sense).

Complications of Tourniquet Use

Local

• Neuropraxia.
• Muscle ischaemia and necrosis.
• Vascular injury.
• Post-release swelling and joint stiffness.
• Haematoma formation.
• Delayed recovery of muscle power.

Systemic

• Embolism of fat and metabolites.
• Cardio-respiratory decomposition (not conclusively proven).

Neuropraxia

• Resolves within 3 months.
• Affects motor and sensory functions (temperature sensation preserved).
• Pulses, skin appearance, and temperature are normal.
• EMG findings: Conduction block at the level of the tourniquet.

Muscle Ischaemia

• Re-perfusion injury to the muscle.
• Longer tourniquet times = higher CK levels and more tissue ischaemia.
• Tissue markers normalize between 2 and 20 minutes after reperfusion.
• No evidence that deflating and re-inflating the tourniquet improves safety.

Myonephrotic Metabolic Syndrome

• Rare, occurs in severe ischaemia.
• Features:
  • Renal failure.
  • Metabolic acidosis.
  • Myoglobinuria.
  • Hyperkalaemia.

Tourniquet Deflation

• No evidence that tourniquet use increases the risk of DVT or PE after deflation.
• Precautions:
  • Monitor patients undergoing intramedullary procedures for sudden fat or metabolite embolism.
• Effects of Deflation:
  • Increases production of antithrombin 3 and Protein C, leading to increased bleeding and reduced clotting.

Tourniquet Release in Total Knee Replacement (TKR)

• Pre-closure deflation:
  • Increases blood loss and transfusion needs.
  • Associated with increased infection risk.
• Post-closure deflation:
  • More likely to require return for wound washout.
• Surgeon’s Discretion:
  • Balance between minimizing blood loss and reducing infection risk.