Tourniquet- Implications for anaesthesiologists

Prakash K. Dubey
Professor of Anaesthesia
Indira Gandhi Institute of Medical Sciences, Patna, INDIA

A tourniquet is a compressing device, which controls venous or arterial circulation to an extremity. It is used commonly during limb surgery and intravenous regional anaesthesia. Tourniquet has been in use since the early Roman times. Jean Louis Petit in 1718 coined the term ‘Tourniquet’ (French ‘Tourner’, meaning ‘to turn’) In 1873, Johann Friederich August von Esmarch described the flat rubber tourniquet. Harvey Cushing, in 1904, first used the pneumatic tourniquet.
A pneumatic tourniquet consists of an inflatable cuff, a compressed gas source and a device to maintain cuff pressure at a set level. Microprocessor based devices that do not require compressed gas is now available. There are physiological alterations and other safety issues related to arterial tourniquets that have important implications for anaesthesiologists, well described by Kam et al.[1]

1. Pathophysiological effects 

All tourniquets can have local or systemic pathophysiological consequences ranging from being self limiting to fatal. [1,2]      
Local complications result from pressure to underlying tissue or distal ischaemia depending on amount and duration of the pressure applied.

1. Nerve injury: may range from paraesthesia to paralysis, more commonly in upper limb. Radial and sciatic are most frequently affected. Exsanguination of a limb should be achieved by elevation of the arm or leg for 5 minutes at 90º and 45º respectively without compression [3] rather than using the Esmarch bandage tourniquet that can generate pressures up to 1000 mm of Hg and is notorious for nerve injury.

Intraneural microvascular changes and oedema form due to nerve compression, which leads to axonal degeneration. Nodes of Ranvier are damaged due to nerve compression. The nerve injury mostly heals spontaneously within six months. The likelihood of neurologic dysfunction increases with total tourniquet time and a reperfusion interval modestly decreases the risk of nerve injury. [4] 

1. Muscle injury: Muscle cells undergo hypoxia and hypercapnia beneath the tourniquet following anaerobic metabolism. Ischaemia and mechanical distortion leads to depletion of creatine phosphate, glycogen, adenosine triphosphate and increase in lactate.

After 2-4 hours of ischaemia, microvascular injury from compression and endothelial injury from superoxide radicals together cause an increase in microvascular permeability in muscle and nerve tissue. The resultant interstitial and intracellular oedema may take long to resolve, may cause rhabdomyolysis or a compartment syndrome. [5] “Post tourniquet syndrome” can develop that is characterized by stiffness, pallor, weakness without paralysis and subjective numbness of the extremity without objective anaesthesia.

1. Vascular injury: Arterial injury, although rare, is commonly seen in lower limb surgery in patients with peripheral vascular disease. Mechanical pressure from tourniquet traumatizes atheromatous vessels, causing plaque fracture and the lack of blood flow leads to thrombosis. Tourniquet should be avoided in patients with absent distal pulse, poor capillary return, calcified femoropopliteal system or a history of vascular surgery on the involved limb.[6]
2. Skin injury: Although uncommon, is caused by pressure necrosis or friction burns produced by poorly applied tourniquet. In children and elderly, chemical burn may be caused by skin preparation solution that had seeped beneath the cuff.[7]

Systemic complications take place due to inflation and deflation of the tourniquet.

1. Respiratory: Although tourniquet inflation has insignificant respiratory effect, deflation leads to an increase in end tidal carbondioxide concentration by 0.1-2.4kPa. The peak effect is within one minute that normalizes within 10 minutes. Deflation causes a return of hypercapnic venous blood into systemic circulation and this increase is greater with release of lower limb tourniquets. Spontaneously breathing patients respond to this carbondioxide load by increase in minute ventilation for 5 minutes and this can be prevented during controlled ventilation by increasing the minute ventilation by 50% for 5 minutes prior to deflation. [8]
2. Cardiovascular: Following exsanguination and inflation, circulating blood volume and systemic vascular resistance increases leading to a transient increase in central venous pressure and systolic blood pressure. After deflation, central venous pressure and blood pressure decrease for 15 minutes due to a shift of blood volume back into the limb and post ischaemic reactive hyperaemia associated with a decrease in peripheral vascular resistance. Circulatory overload and cardiac arrest have been reported in patients with bilateral thigh tourniquets. [9]
3. Tourniquet Pain: After 30-60 minutes, there is a second surge in heart rate and blood pressure that persists till tourniquet deflation and is resistant to analgesics, depth of general anaesthesia and sensory anaesthesia of the underlying dermatome during regional blocks.[1] The incidence increases with increasing age and duration of surgery. It is more common in lower limb surgery and the hypertension is greater during general anaesthesia as compared to regional techniques.

It is thought that the unmyelinated C fibres, that are normally inhibited by myelinated A fibres, mediate this pain. [1] After cuff inflation, A δ fibres are blocked by compression thus taking away the post-synaptic inhibition of C fibres. This is supported by the finding that C fibres are more resistant to local anaesthetics. Another theory suggests that nerve compression and ischaemia causes a block of input to low threshold mechanoreceptor neurons in the dorsal horn of spinal cord that have receptive field distal to the tourniquet cuff. An increased spontaneous activity of the high threshold nociresponsive neurons located proximal to the tourniquet leads to an expansion of the receptive field and may explain the mechanism of this pain. [10].
During spinal and epidural techniques, the larger nerve fibres carrying pressure-pain sensation may not be blocked causing pain despite adequate sensory anaesthesia. Addition of adrenaline, morphine, clonidine, alkali, dexmedetomidine to local anaesthetics, intravenous ketamine and oral gabapentine have been tried to obtund this response.

1. Cerebrovascular: Hypercarbia following tourniquet deflation may lead to 50% increase in middle cerebral artery blood flow which peaks within 5 minutes and settles within 10 minutes. This may cause secondary brain injury in patients with raised intracranial pressure and can be attenuated by predeflation hyperventilation.
2. Haematological: After tourniquet inflation, platelet aggregation leading to hypercoagulability is promoted due to catecholamine release following tourniquet pain and tissue compression by Esmarch bandage. Following deflation, an increased thrombolytic activity is seen due to release of tissue plasminogen activator resulting from tissue ischaemia, anoxia and acidosis. This brief period (30 minutes) of reduced coagulability has been implicated in post-tourniquet bleeding. [1]
3. Thermal:  Inflation raises core body temperature because of reduced metabolic heat transfer from central compartment to periphery whereas tourniquet deflation decreases the temperature by redistribution of body heat and return of hypothermic blood from the ischaemic limb.
4. Metabolic: Tourniquet release following upto 2hours of ischaemia causes increase in plasma potassium and lactate concentration, carbondioxide and a decrease in pH. All these values settle to baseline within half an hour. [1]

The release of tourniquet may cause an ischaemia reperfusion injury. [11] Massive and abrupt release of oxygen free radicals after reperfusion, followed by endothelial dysfunction or neutrophil infiltration, triggers the oxidative damage. Pulmonary complications and arrhythmias have been reported on limb ischemia-reperfusion injury and can be of concern, especially in older patients receiving total knee replacement. Propofol has been found to possess a preventive effect on free radical formation acting as a free radical scavenger.

1. Pharmacokinetics: Pharmacokinetics of drugs may be modified as drugs administered before cuff inflation may become sequestrated in the isolated limb and get redistributed on deflation. Similarly, drugs administered after cuff inflation may have a reduced volume of distribution. 

It is recommended to inflate the tourniquet at least 5 minutes after intravenous administration of antibiotics for optimal tissue penetration. [1]

1. Safety issues

There are other issues related to tourniquet safety that an anaesthesiologist should be aware of to prevent complications. 

1. Tourniquet time: Although controversial, mostly it is recommended not to exceed 2 hours in healthy patients. It has also been suggested to release the tourniquet hourly for 10 minutes to allow reperfusion for prolonged tourniquet use. [1] Others have recommended applying two tourniquet cuffs, to be inflated alternately at hourly interval without a reperfusion period. [12] Precooling of the limb 30 minutes before applying tourniquet increases the inflation time to 4 hours.
2. Tourniquet pressure: It is prudent to use the lowest pressure that causes arterial occlusion. Use of a wider cuff and a variable-fit contour cuff is advocated. [13] The American Association of Perioperative Registered Nurses recommends tourniquet pressure based on Limb Occlusion Pressure (LOP). LOP is defined as the minimum pressure required, at a specific time in a specific tourniquet cuff applied to a specific patient’s limb at a specific location. [14] This can be done by palpation, Doppler or plethysmography. A safety margin is added to LOP to compensate for intraoperative blood pressure fluctuations (40mmHg for LOP less than 130mmHg, 60mmHg for LOP between 130-190mmHg and 80mmHg for LOP more than 190mmHG). Modern tourniquet systems include means to measure LOP automatically. 
3. Contraindications/Precautions: Although there is no absolute contraindication to tourniquet application, adequate precautions should be taken in patients with; severe peripheral vascular disease, sickle cell disease, severe crush injury, diabetic neuropathy, left ventricular dysfunction, history of deep vein thrombosis or pulmonary embolism, morbid obesity and raised intra cranial pressure.
4. Paediatric use: Apart from the usual precautions, the tourniquet pressure should be set at LOP plus a safety margin of 50 mmHg for normotensive paediatric patient having a normal limb. A limb protection sleeve specifically designed for the selected cuff should be applied. In the event that arterial blood flow is observed past the tourniquet cuff, tourniquet pressure should be increased in 25 mmHg increments until blood flow stops. The tourniquet time should be minimized.
5. Good clinical practice: Proper maintenance of the equipment and training of personnel is vital to prevent complications. Inspection and selection of cuff, pressure gauge calibration, and leaks etcetera should be checked before use. Proper application of padding and cuff should be practiced. Inflation time and pressure recommendations should be followed. A thorough inspection of the limb should be performed after the procedure and documentation of the tourniquet usage should be recorded in the patient’s notes. 

1. Other uses of tourniquet:

Several other uses of the tourniquet important for anesthesiologists are;

1. Isolated limb perfusion in the management of localized malignancy.
2. Intravenous regional sympathectomy in management of complex regional pain syndrome.
3. Isolated forearm technique to monitor awareness during general anaesthesia developed by Tunstall.
4. As a first aid measure in battle fields to control acute haemorrhage.
5. Limb remote ischemic preconditioning, a physiologic mechanism whereby skeletal muscles exposed to a transient sub lethal episode of ischaemia / reperfusion develops resistance to subsequent ischemic insult of remote vital organs. [15]

Awareness of these mechanical and physiological effects of the tourniquet usage in the operation room will help us understand the good, bad and the evil consequences of a tourniquet.

 

 

References:

1. Kam PCA, Kavanaugh R, Yoong FFY. The arterial tourniquet: pathophysiological consequences and anaesthetic implications. Anaesthesia 2001;56:534-45
2. tourniquets.org [internet] ©2014, J.A.McEwen [last updated May 2014] Available from  http://www.tourniquets.org/
3. Warren PJ, Hardman PJ, Woolf VJ, Limb exsanguinations II. The leg: effect of angle of elevation. Ann R Coll Surg Engl 1992;74:323-5
4. Horlocker TT, Hebl JR, Gali B, Jankowski CJ, Burkle CM, Berry DJ, Zepeda FA,  Stevens SR, Schroeder DR. Anesthetic, patient, and surgical risk factors for neurologic complications after prolonged total tourniquet time during total knee arthroplasty. Anesth Analg 2006;102:950 –5
5. Greene TL, Louis DS. Compartment syndrome of the arm- a complication of the pneumatic tourniquet. J Bone Joint Surg Am 1983;65:270-3
6. Kumar SN, Chapman JA, Rawlins I. Vascular injuries in total knee arthroplasty: a review of the problem with special reference to the possible effects of the tourniquet. J Arthroplasty 1998;13:211-6
7. Dickinson JC, Bailey BN. Chemical burns beneath tourniquets. Br Med J 1998;297:1513
8. Bourke DL, Silberberg MS, Ortega R, Willock MM. Respiratory responses associated with release of intraoperative tourniquets. Anesth Analg 1989;69:541-4
9.  Maurer NH, Voegeli PT, Sorkin BS. Non-cardiac circulatory overload secondary to pneumatic thigh tourniquets. J Am Podiatry Assoc 1983;73:589-92
10. Crews JC, Cahall MA. An investigation of the neurophysiologic mechanism of tourniquet related pain: changes in spontaneous activity and receptive field size in spinal dorsal horn neurons. Reg Anesth Pain Med 1999;24:102-9
11. Cheng YJ, Wang YP, Chien CT, Chen CF. Small-dose propofol sedation attenuates the formation of reactive oxygen species in tourniquet-induced ischemia-reperfusion injury under spinal anesthesia. Anesth Analg 2002;94:1617–20
12. Neimkin RJ, Smith RJ.  Double tourniquet with linked mercury manometer for hand surgery. J Hand Surg Am1983;8:938-41
13. McEwen JA, Inkpen KB, Younger A. Thigh tourniquet safety: Limb occlusion pressure measurement and a wide contoured cuff allow lower cuff pressure. Surg Tech 2002;34:8–18.
14. Reilly CW, McEwen JA, Leveille L, Perdios A, Mulpuri K. Minimizing tourniquet pressure in pediatric anterior cruciate ligament reconstructive surgery: a blinded, prospective randomized controlled trial. J Pediatr Orthop 2009;29:275-280
15. Li C, Xu M, Wu Y, Li YS, Huang WQ. Ke-Xuan Liu, Limb remote ischemic preconditioning attenuates lung injury after pulmonary resection under propofol–remifentanil anesthesia. Anesthesiology 2014;121:249-59.