Applied Physiology for the Final SOE

• For lower limb use double the systolic pressure up to 150 mmHg above systolic
• For upper limb use 50 mmHg above systolic

• Limb surgery requiring a bloodless field
• Intravenous regional anaesthesia
• Control of catastrophic haemorrhage from injured limb

As always, divide into absolute and relative.

Absolute

• AV fistula
• Suspected DVT
• Concern about disseminating infection or malignancy

Relative

• Peripheral artery disease
• Significant crush injury
• Peripheral neuropathy
• Loss of skin integrity
• Sickle cell
• Raynaud's disease

This can be divided into local and systemic.

Local

• Muscle injury
• Nerve injury - particularly radial and sciatic
• Vascular injury
• Skin damage

Systemic

Cardiovascular

• Small increase in systemic vascular resistance
• Increase in venous return can theoretically cause fluid overload in cardiac patients
• Blood pressure and heart rate will increase with increasing duration of tourniquet time - this effect is reduced for lower limb tourniquets with spinal anaesthesia

Respiratory

• DVT and PE risk

Metabolic

• Anaerobic metabolism in the limb leads to accumulation of metabolic waste
• This can lead to acidosis
• Infection can theoretically be encouraged to spread by applying a tourniquet

Pain

• Due to a combination of direct pressure, acidosis and ischaemia

• 2 hours in an otherwise healthy patient
• Less for elderly or unwell patients
• If it's going to take longer then the tourniquet needs to be deflated for ten minutes after 1.5 hours to allow reperfusion

Probably best to work through this in a chronological fashion.

• Tourniquet deflates, releasing arterial pressure and reducing systemic vascular resistance
• Blood flow is diverted to previously occluded limb
• Venous return to the heart transiently decreases, causing a drop in blood pressure and a compensatory tachycardia
• Cold blood full of metabolic waste is flushed (including lactate, CO2 and potassium) is flushed into the venous system, causing a transient and mild drop in core temperature
• Acidosis, hyperkalaemia and hypothermia can lead to arrhythmias and labile blood pressures in frailer patients or after a long tourniquet time
• The excess CO2 is delivered to the lungs, causing an increase in EtCO2

Complications are rare at around 0.04%, but can be significantly debilitating.

• Usually nerve injury is the issue
• Mostly this will resolve by itself within six months
• Higher risk with lower limb tourniquets than upper limb
• Bigger nerve = higher risk of compressive damage
• Esmarch bandages can be surprisingly powerful and cause nerve damage by generating upwards of 1000 mmHg of pressure
• Compartment syndrome and rhabdomyolysis are possible if there is significant oedema after reperfusion
• Skin injuries can occur if inappropriately applied
• Arterial injury is possible, especially in peripheral vascular disease