Vol 9, No 5, September/October 2001 345 The pneumatic tourniquet was introduced in 1904 by Harvey Cushing to maintain a bloodless field during extremity surgery. Since then, its use has become almost routine, and the widespread assumption that maintaining a bloodless field is of prime impor- tance leads many surgeons to lose sight of the potentially dangerous nature of this piece of equipment. 1 Modern pneumatic tourniquets are designed to minimize the inci- dence of complications, and pro- spective randomized clinical trials have shown no significant long-term deleterious effects of using them in extremity surgery. 2,3 Nevertheless, their use is still associated with potentially serious morbidity 4-8 and even mortality. 9 Therefore, it is im- portant for orthopaedic surgeons to be knowledgeable about the patho- physiology of tourniquet-induced skeletal-muscle ischemia-reperfusion injury and the potential pitfalls of using pneumatic tourniquets. Advances in molecular biology are increasing our understanding of the effects of tourniquet-induced ischemia-reperfusion injury at the cellular level, allowing the develop- ment of more scientifically valid guidelines for safe application times and inflation pressures. Pneumatic Tourniquet Design and Care A modern pneumatic tourniquet system comprises several compo- nents that allow safe and precise regulation of cuff pressure to mini- mize complications resulting from excessive inflation or accidental deflation of the cuff intraopera- tively. Compressed gas is used for tourniquet inflation. The gas may be nitrogen or air, from either a cylinder or a piped central supply. Freon, an ozone-depleting chloro- fluorocarbon previously used for inflation in pneumatic tourniquet systems, was banned in the United States in 1996 for environmental safety reasons. A modern system allows one to preset the pressure before inflation. Subsequently, a microprocessor ensures self-compensation, main- taining a constant preset cuff pres- sure during limb movements and changes in limb size. A maximum- pressure device prevents applica- tion of excessively high pressures (>600 mm Hg). Additional safety is provided by a supply monitor that shuts the system down while maintaining cuff pressure if the gas or air supply is interrupted or if a leak occurs intraoperatively. Dr. Wakai is Denis O’Sullivan Research Fellow, Department of Academic Surgery, Cork University Hospital, Cork, Ireland. Dr. Winter is Senior Resident, Department of General Surgery, Cork University Hospital. Dr. Street is Research Fellow, Academic Surgery De- partment, Cork University Hospital. Dr. Redmond is Professor of Surgery, University College Cork, and Consultant Surgeon, Cork University Hospital. Reprint requests: Dr. Wakai, Department of Academic Surgery, Cork University Hospital, Cork, Ireland. Copyright 2001 by the American Academy of Orthopaedic Surgeons. Abstract Pneumatic tourniquets maintain a relatively bloodless field during extremity surgery, minimize blood loss, aid identification of vital structures, and expedite the procedure. However, they may induce an ischemia-reperfusion injury with potentially harmful local and systemic consequences. Modern pneumatic tourniquets are designed with mechanisms to regulate and maintain pressure. Routine maintenance helps ensure that these systems are working properly. The complications of tourniquet use include postoperative swelling, delay of recovery of muscle power, compression neurapraxia, wound hematoma with the potential for infection, vascular injury, tissue necrosis, and compartment syn- drome. Systemic complications can also occur. The incidence of complications can be minimized by use of wider tourniquets, careful preoperative patient eval- uation, and adherence to accepted principles of tourniquet use. J Am Acad Orthop Surg 2001;9:345-351 Pneumatic Tourniquets in Extremity Surgery Abel Wakai, MB, Desmond C. Winter, MD, John T. Street, MB, and Paul H. Redmond, MCh Pneumatic Tourniquets in Extremity Surgery Journal of the American Academy of Orthopaedic Surgeons 346 Inaccurate gauges and malfunc- tioning valves can allow excessively high inflation cuff pressures, which can lead to complications. Therefore, pneumatic tourniquets should be kept in good condition by routinely checking all valves and gauges. Specific recommendations include daily calibration checks, intraopera- tive monitoring of tourniquet func- tion at frequent intervals, and rigor- ous monthly performance-assurance tests. 10 These monthly tests involve determination of whether the actual pressure is accurate to within 5% of the set pressure and remains stable to within 10% of the set pressure over a 15-minute period, as well as whether the hysteresis exceeds 200 mm Hg. 10 Tourniquet Application Application of a pneumatic tourni- quet should be performed only by experienced personnel who are knowledgeable about its use and potential complications. Prior to tourniquet application, it is essen- tial to note coexistent medical con- ditions, such as peripheral vascular disease, the presence of an underly- ing prosthetic vascular graft, exten- sive soft-tissue injury, or sickle cell disease. In some circumstances, these conditions may increase the risk of tourniquet-related complica- tions and may, therefore, represent a relative contraindication to tourni- quet use. Certain precautions may be necessary to avoid such compli- cations. For example, it is safe to use tourniquets on patients with sickle cell disease provided they are well oxygenated and their acid-base status is optimized perioperatively. 11 The tourniquet should be tested by inflation and then completely deflated before application. The limb is generally exsanguinated first, either by elevating it for 3 to 5 minutes or by applying a soft rub- ber compression bandage. Alterna- tively, the tourniquet may be inflated without exsanguination, particularly if there is an area of sepsis in the limb. The tourniquet should be padded with a soft dressing to prevent the wrinkles and blisters that may occur when the skin is pinched. It should be applied to the upper arm or thigh, where there are adequate muscle envelopes to protect invested nerves from compression. After tourniquet application, inflation should be rapid to prevent filling of the superficial veins before arterial occlusion. Deflation before wound closure allows iden- tification and coagulation of major bleeding vessels. Inflation Pressure The pressure to which the tourni- quet should be inflated depends on the patient’s blood pressure and the shape and size of the extremity. For example, for conical extremities in very muscular or obese individuals, curved cuffs are ideal because they require lower arterial occlusion pressures than straight (rectangular) cuffs. 12 Wide cuffs have been found to be more effective at lower infla- tion pressures than narrow ones are. Crenshaw et al 13 studied the effect of pneumatic tourniquet cuff size on transmission of pressure to deeper tissues and on elimination of limb blood flow. Measurements of tissue fluid pressure at four depths in cadaver limbs (Fig. 1) showed that wide cuffs provided a broader plateau of tissue compression at all tissue depths and transmitted a greater percentage of the applied tourniquet cuff pressure to deeper tissues (Fig. 2). The tissue-fluid pressure was always maximal at midcuff. Furthermore, by determin- ing pulse elimination pressure (the pressure required to eliminate a pulse detectable by a Doppler de- vice), wide cuffs required lower cuff pressures for elimination of Figure 1 Longitudinal views of cadaver leg and arm showing placement of tourniquet cuffs and initial positions of catheters at four tissue depths: (1) subcutaneous, (2) subfas- cial, (3) midmuscle, and (4) near bone. Cross sections of leg and arm show catheter depth within the limbs. (Adapted with permission from Crenshaw AG, Hargens AR, Gershuni DH, Rydevik B: Wide tourniquet cuffs more effective at lower inflation pressures. Acta Orthop Scand 1988;59:447-451.) 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 To pressure transducers 18-cm cuff 12-cm cuff Abel Wakai, MB, et al Vol 9, No 5, September/October 2001 347 blood flow to the operative site and achievement of adequate hemosta- sis (Fig. 3). Several methods have been proposed for determination of the optimal inflation pressure for extremity surgery 14-16 (Table 1). Tourniquet Ischemia and Posttourniquet Syndrome Interruption of blood supply leads to tissue hypoxia and acidosis. 17 This is associated with increased capillary permeability 18 and blood coagulation changes. 19 Depletion of high-energy phosphate occurs with subsequent loss of physiologic ion gradients across the cell mem- brane due to impaired sodium pump activity. 20 Ultimately, if the interruption of blood supply is of sufficient duration, cellular necro- sis results. The severity of tourniquet ische- mia is tissue- and species-dependent and is influenced by the duration of ischemia and the presence of adequate collateral circulation. Tourniquet- induced ischemia has been exten- sively studied in rat muscles. How- ever, one must bear in mind that the myocytes of small animals are more sensitive to ischemia than those of ca- nine and human skeletal muscle. 21,22 In a canine model, 3 hours of sus- tained tourniquet ischemia resulted in widespread reversible sublethal injury to skeletal myocytes. 22 Furthermore, muscle is more sus- ceptible to ischemic injury than is any other tissue of the extremity. 23 Two hours or more of sustained is- chemia during extremity surgery in humans may lead to “posttourni- quet syndrome,” 4 which is character- ized by edema, stiffness, pallor, weakness without paralysis, and subjective numbness of the extremity without anesthesia. Posttourniquet syndrome is thought to be the most common, yet least appreciated, form of morbidity due to tourni- quet use. 22 Its incidence is perhaps underestimated because of the rou- tine concealment of the limb in a cast or dressing postoperatively. The posttourniquet syndrome usually resolves within 1 week, although the recovery period may be pro- longed. 4 Tissue ischemia may elicit neu- rally mediated systemic cardiovas- cular responses characterized by a reflex generalized sympathetic pressor response. 24 The mecha- nisms underlying this phenomenon and its clinical relevance have not been fully elucidated. Such reflex responses may play a role in the pathogenesis of the arterial hyper- tension associated with pneumatic tourniquet use (“tourniquet hyper- tension”). 25 Tourniquet Application Time Although there has not been a pro- spective randomized clinical trial defining the optimal tourniquet- application times in lower limb sur- gery, 2 hours is considered safe for human upper limb surgery. 26 The serum creatine phosphokinase (CPK) concentration is elevated in response to muscle damage at and distal to the tourniquet cuff and has been employed as an indicator in studies on safe tourniquet applica- tion times. Elevation of CPK levels does not occur after 1 hour of canine hind-limb ischemia, but does occur after 2 or 3 hours of ischemia. 22,27 Limiting tourniquet application to 1.5 hours avoids CPK elevations due to skeletal-muscle ischemic injury in experimental studies. 22,27 In the clinical setting, tourniquet times of 2 hours or less have not been associated with major adverse 200 100 0 -5 0 5 10 15 20 Subcutaneous Subfascial Midmuscle Near bone 200-mm Hg Cuff Pressure 12-cm Cuff on 6 Arms Tissue Fluid Pressure, mm Hg Distance From Proximal Edge of Cuff, cm 200 100 0 -5 0 5 10 15 20 25 200-mm Hg Cuff Pressure 18-cm Cuff on 6 Legs Distance From Proximal Edge of Cuff, cm Tissue Fluid Pressure, mm Hg 400 200 100 300 0 -5 0 5 10 15 20 400-mm Hg Cuff Pressure Distance From Proximal Edge of Cuff, cm Tissue Fluid Pressure, mm Hg 400 200 100 300 0 400-mm Hg Cuff Pressure Distance From Proximal Edge of Cuff, cm -5 0 5 10 15 20 25 Tissue Fluid Pressure, mm Hg Figure 2 Distribution of tissue-fluid pressures in cadavers at four tissue depths beneath a 12-cm cuff on six arms and an 18-cm cuff on six legs. Pressure was applied at 200 mm Hg and 400 mm Hg. (Adapted with permission from Crenshaw AG, Hargens AR, Gershuni DH, Rydevik B: Wide tourniquet cuffs more effective at lower inflation pressures. Acta Orthop Scand 1988;59:447-451.) Pneumatic Tourniquets in Extremity Surgery Journal of the American Academy of Orthopaedic Surgeons 348 effects. 26 This is a useful guideline for current clinical practice until tourniquet-application times are better defined on the basis of cellu- lar changes during skeletal-muscle reperfusion injury. Short periods of ischemia fol- lowed by reperfusion (“ischemic preconditioning”) render skeletal muscle more resistant to subsequent ischemic episodes. 28 Although this phenomenon has been exploited in cardiac surgery for myocardial pro- tection and preservation during coronary artery bypass grafting, it is not yet used to prolong tourniquet- application time in extremity sur- gery. Hypothermia has been shown to attenuate ischemic damage in rat skeletal muscle 29 and to prolong tourniquet-application time in canine skeletal muscle ischemia- reperfusion injury. 30 Controlled tri- als are required before these strate- gies can be recommended as a means of safely prolonging tourniquet ischemia in the clinical setting. Reperfusion After Tourniquet Deflation Ischemia primes the tissue for the injury that occurs during reperfu- sion. Nevertheless, reperfusion is necessary for ischemic tissue to restore energy supplies and remove toxic metabolites. The return of toxic metabolites to the circulation results in systemic metabolic dys- function (“myonephropathic meta- bolic syndrome”), which is char- acterized by metabolic acidosis, hyperkalemia, myoglobinemia, myoglobinuria, and renal failure. 31 Reperfusion injury was originally thought to be mediated by free radi- cals and activated polymorphonu- clear leukocytes, but other media- tors have been implicated, including nitric oxide, cytokines, and arachi- donic acid metabolites. 32,33 Modula- tion of these factors may ameliorate skeletal muscle ischemia-reperfusion injury and lead to prolongation of operative time under tourniquet control. However, as yet there have been no published clinical studies. Loss of ion gradients across the cell membranes of ischemic myo- cytes results in leakage of potassium ions into the interstitium. 20 Mean- while, release of intracellular en- zymes (CPK, lactic acid dehydrogen- ase, and glutamic-oxaloacetic trans- aminase) and myoglobin may occur due to rhabdomyolysis. 6,32 Precipi- tation of myoglobin in the collecting tubules of the kidneys may induce acute renal failure and metabolic acidosis 31 ; the resulting hyperka- lemia may lead to sudden death. 34 Complications The use of pneumatic tourniquets is associated with some level of mor- bidity 4-8 and infrequent mortality 9 (Table 2). However, there is a paucity of information regarding the incidence of individual compli- Thigh Circumference, cm 400 360 320 280 240 200 160 120 80 30 40 50 60 70 80 4.5 cm ( ) (r=0.89) 8 cm ( ) (r=0.82) 12 cm ( ) (r=0.73) 18 cm ( ) (r=0.44) Pulse Elimination Pressure, mm Hg Figure 3 The relationship between pulse elimination pressure and thigh circumference for four cuff widths. Dashed lines represent a best-fit linear regression corresponding to each width. Correlation coefficients are expressed as r values. (Adapted with permission from Crenshaw AG, Hargens AR, Gershuni DH, Rydevik B: Wide tourniquet cuffs more effec- tive at lower inflation pressures. Acta Orthop Scand 1988;59:447-451.) Table 1 Methods Used to Determine Pneumatic Tourniquet Inflation Pressure Add 50-75 mm Hg to the pressure required to obliterate the peripheral pulse when using a Doppler stethoscope, to allow for collateral circulation and blood pressure changes 14 Add 90-100 mm Hg to the preoperative systolic arm blood pressure for lower limb surgery 15 Add 50-75 mm Hg and 100-150 mm Hg above the systolic arm blood pressure for upper and lower limb surgery, respectively 16 Abel Wakai, MB, et al Vol 9, No 5, September/October 2001 349 cations. The tissues at greatest risk from tourniquet use are nerve and muscle. 21-23 Although muscle is more susceptible to ischemic injury than any other tissue in the extremi- ty, 22,23 the most common complica- tions in the clinical setting are neur- al, including ischemic neuropathy and compressive neurapraxia. 21,22 Compressive neurapraxia, rather than ischemic neuropathy or muscle damage, is considered to be the un- derlying cause of “tourniquet paral- ysis.” 35 The reported incidence of soft-tissue damage and tourniquet paralysis is 0.15%. 10 Functional and microscopic changes, which may be short-lived or prolonged, occur in muscle due to tourniquet injury. There is a demon- strable delay in recovery of straight- leg-raising power after knee surgery performed under tourniquet con- trol. 36 Although this postoperative quadriceps weakness may be attrib- uted to pain and ischemic myopa- thy, compressive neurapraxia may be contributory. 36 This impairment of skeletal muscle function is of po- tential significance because it may adversely affect and prolong patient rehabilitation. Changes in circulatory volume result from limb exsanguination and the reactive hyperemia induced by tourniquet release. 37 This can result in circulatory and respiratory com- plications. 7,9 Hemodynamic changes are more marked with simultaneous use of tourniquets on both lower limbs. 38 Therefore, simultaneous deflation of tourniquets should be avoided when bilateral simultaneous total knee arthroplasty is performed with a single anesthetic administra- tion. Other cardiovascular sequelae of tourniquet use include arterial hy- pertension 25 and increased central venous pressure. 38 Tourniquets may also cause direct vascular injury, par- ticularly if the vessel wall is dis- eased. 39,40 In addition, pneumatic tourniquets induce venous stasis and increased platelet adhesion in the valve pockets after distal limb ischemia. 41 These effects may ac- count for the reportedly higher postoperative incidences of veno- graphically diagnosed deep venous thrombosis after total knee arthro- plasty (80%) than after total hip ar- throplasty (50%) in patients who did not receive postoperative anti- coagulant prophylaxis. 13,42 However, the evidence regarding the effect of using pneumatic tourniquets on the incidence of postoperative deep venous thrombosis is contradic- tory. 41-43 Nevertheless, with or without tourniquet use, a hyperco- agulative state occurs after total knee arthroplasty, 19 and there is no indication to alter current guidelines for perioperative anticoagulant pro- phylaxis. Reactive hyperemia after tourni- quet deflation causes a 10% increase in limb size, resulting in postopera- tive swelling and stiffness. 37 The in- crease in soft-tissue tension may be responsible for thigh pain at the tourniquet site. In addition, post- ischemic edema may underlie the increased incidence of wound infec- tion seen in tourniquet-controlled surgery. 43,44 Avoiding Complications Several measures can be taken to minimize the risk of complications associated with using pneumatic tourniquets (Table 3). As men- tioned previously, wider cuffs arrest flow at lower inflation pressures (Figs. 1-3). 16 Therefore, use of such cuffs may reduce the incidence of tissue necrosis, compression neura- praxia, and direct vascular injury. Table 2 Potential Complications of Use of Pneumatic Tourniquets Local Postoperative swelling and stiffness Delay in recovery of muscle power Compression neurapraxia Wound hematoma Wound infection Direct vascular injury Bone and soft-tissue necrosis Compartment syndrome Systemic Increased central venous pressure Arterial hypertension Cardiorespiratory decompensation Cerebral infarction Alterations in acid-base balance Rhabdomyolysis Deep venous thrombosis (evidence is contradictory) Table 3 Measures to Avoid Complications Due to Use of Pneumatic Tourniquets Carefully select patients preoperatively Use a wide low-pressure tourniquet cuff Do not exceed tourniquet ischemia time of 2 hr Alternate the use of two tourniquets Ensure good padding beneath the tourniquet Do not allow any solution applied to the skin to run beneath the tourniquet Carefully monitor perioperative hemodynamic status of patients with poor cardiopulmonary reserve Achieve regional hypothermia by cooling the extremity (not currently part of routine clinical practice) Pneumatic Tourniquets in Extremity Surgery Journal of the American Academy of Orthopaedic Surgeons 350 Alternate inflation of two tour- niquets reduces the direct pressure time at each cuff. In addition, pad- ding beneath the tourniquet dis- tributes pressure more evenly and avoids skin pinching. Antiseptic solutions should be prevented from running beneath the tourniquet to avoid local skin damage. Regional hypothermia reduces limb edema 45 and may preserve peripheral nerve function after ischemia. 29 Prolonged tourniquet application time may lead to a compartment syndrome and should be avoided. In a protracted (>3 hours) extremity procedure, a 30-minute interval is recommended after 2 hours of is- chemia before tourniquet reinfla- tion. 46 This “breather” period suffi- ciently allows normalization of the systemic metabolic effects of tourni- quet release. 17,46 Careful perioperative hemody- namic monitoring is mandatory in patients with poor cardiopulmonary reserve who are undergoing extrem- ity surgery under tourniquet con- trol. The type of anesthesia may also influence the incidence of car- diovascular complications. Arterial hypertension (tourniquet hyperten- sion) has a higher incidence with general anesthesia (67%) than with spinal anesthesia (2.7%) and brachial plexus blockade (2.5%). 25 In addition, general anesthesia with mechanical ventilation attenuates the cardiovas- cular compensatory mechanisms associated with tourniquet release. 46 Regional anesthesia (brachial plexus and spinal blockade) is the technique of choice for avoiding cardiovas- cular complications in tourniquet- controlled surgery, particularly in elderly patients with poor cardiopul- monary reserves. 25,46 Patient selection may also be impor- tant in avoiding tourniquet-related complications. In the absence of prospective randomized studies addressing this issue, any patient selection recommendations have to be based on case reports and theo- retical considerations. Patients who might be at increased risk for such complications include those with poor cardiopulmonary or renal re- serve, clinically significant acid-base imbalance, intracardiac shunts (for atrial septal defects or patent fora- men ovale), or severe peripheral vascular disease. If severe peripheral vascular disease is suspected, a care- ful preoperative evaluation may be helpful to determine the relative risks and benefits of using a tourni- quet. This may involve angiography (for assessment of the status of the distal arterial system) and Doppler determination of segmental pres- sures (for early detection of evolving arterial lesions). 40 Summary Modern low-pressure, wide-cuff pneumatic tourniquet systems allow more predictable and precise pres- sure regulation at the site of applica- tion. This translates into improved safety for extremity surgery. How- ever, there is a lack of prospective randomized clinical studies defining safe tourniquet-application times. Advances in the characterization of cellular events and specific media- tors involved in skeletal muscle ischemia-reperfusion injury have provided potential targets in the effort to improve the safety of ex- tremity surgery under tourniquet control. Further studies of the cellu- lar effects of tourniquet ischemia- reperfusion injury in the clinical set- ting are required before optimal tourniquet-application times can be established. Until then, the conven- tional upper limit of 2 hours is rec- ommended on the basis of currently available data. References 1. Klenerman L: Is a tourniquet really necessary for knee replacement? J Bone Joint Surg Br 1995;77:174-175. 2. Kirkley A, Rampersaud R, Griffin S, Amendola A, Litchfield R, Fowler P: Tourniquet versus no tourniquet use in routine knee arthroscopy: A prospec- tive, double-blind, randomized clinical trial. Arthroscopy 2000;16:121-126. 3. 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Francis CW, Pellegrini VD, Stulberg BN, Miller ML, Totterman S, Marder VJ: Prevention of venous thrombosis after total knee arthroplasty: Compari- son of antithrombin III and low-dose heparin with dextran. J Bone Joint Surg Am 1990;72:976-982. 43. Abdel-Salam A, Eyres KS: Effects of tourniquet during total knee arthroplas- ty: A prospective randomised study. J Bone Joint Surg Br 1995;77:250-253. 44. Salam AA, Eyres KS, Cleary J, el- Sayed HH: The use of a tourniquet when plating tibial fractures. J Bone Joint Surg Br 1991;73:86-87. 45. Paletta FX, Shehadi SI, Mudd JG, Cooper T: Hypothermia and tourni- quet ischemia. Plast Reconstr Surg 1962;29:531-538. 46. Townsend HS, Goodman SB, Schur- man DJ, Hackel A, Brock-Utne JG: Tourniquet release: Systemic and metabolic effects. Acta Anaesthesiol Scand 1996;40:1234-1237.