Tourniquet Injuries: Mechanisms and Prevention
Surgical Tourniquet Injuries
It is reliably estimated that pneumatic tourniquets are used in more than one million surgical procedures annually in North America. The potential for injury is significant, although the use of lower, personalized tourniquet pressure levels and shorter tourniquet times are reducing the number, nature and extent of reported injuries. Injuries resulting from pneumatic tourniquet use are most commonly pressure-related, resulting either from the use of an excessively high tourniquet pressure level or from the use of an insufficiently low tourniquet pressure level. Ischemic injuries can also result from prolonged tourniquet time periods. The majority of such injuries may be transient, and perhaps not noticed clinically, but some injuries are permanent, or reversible only over extended time periods with prolonged disability being experienced by the afflicted patient.
When using surgical tourniquets, it is best practice to take all reasonable preventive measures to minimize the probability of tourniquet-related complications and injuries. Click here to learn about 10 Best Practices for Surgical Tourniquets.
Complications and injuries related to the use of a surgical tourniquet include :
- Nerve injury
- Post-tourniquet syndrome
- Intraoperative bleeding
- Compartment pressure syndrome
- Pressure sores and chemical burns
- Digital necrosis
- Toxic reactions
- Other complications
1. Nerve Injury
Nerve injury is the most common complication from the use of tourniquets during upper-extremity surgery, and can also occur in thigh and lower leg cuff applications. It was first recognized more than 120 years ago. The extent of nerve injury can range from a mild transient loss of function to permanent, irreversible damage. Symptoms of nerve injury include an inability to detect pain, heat, cold, or pressure over the skin along the source of the nerve; and a sluggishness or inability to move large or small muscles upon command.
Limb paralysis is also referred to as nerve paralysis or tourniquet paralysis syndrome. When this occurs, all motor nerves distal to the cuff are affected, resulting in a temporary or permanent inability to move the extremity. The radial nerve is the most common nerve affected. Symptoms of tourniquet paralysis are: motor paralysis and loss of the sense of touch, pressure, and proprioceptive responses.
Paralysis can produce considerable disability and psychological stress in affected patients. In addition to the impact on the individual patient, nerve injury which results from best practices not being followed may also subject the surgical staff and facility to potential legal liability.
Nerve injury: mechanism
It has been suggested that the incidence of nerve injuries, or so-called tourniquet paresis, may be greatly under-reported, eg [2, 3]. To minimize risk to the patient and potential legal liability, an understanding of both the mechanism of such injuries and possible preventative measures is important.
The basic mechanism of tourniquet-related nerve injury was investigated by Ochoa et al. [4-6]. In experiments with wide tourniquet cuffs, Ochoa et al. discovered a characteristic lesion with anatomical features and distribution suggesting that damage to the nerve fibres is a result of the compression pressure level and the pressure gradients applied from the tourniquet cuff. Single teased nerve fibres that had been compressed underneath a tourniquet cuff were examined under an electron microscope and a characteristic abnormality of the nodes of Ranvier were seen in the large myelinated fibres. Specifically, the node of Ranvier was displaced from its usual position under the Schwann-cell junction and the paranodal myelin was stretched on one side of the node and invaginated on the other side. When examining the distribution of lesions under the cuff, the displacement of the nodes of Ranvier was greatest under the edges of the cuff with relative or complete sparing under the center of the cuff. The direction of displacement of the nodes of Ranvier was away from the cuff towards the uncompressed tissue. Since the pressure gradient is highest at the edges of the cuff, this finding suggests that the pressure gradient within the nerve between its compressed and uncompressed part is the factor responsible for the displacement. Another important finding was that the severity of the displacement of the node of Ranvier was milder in degree at a lower compression pressure level, compared to higher compression pressure levels.
These results reveal that the probability of tourniquet-based nerve injury increases as the pneumatic tourniquet pressure level increases, and as the pressure gradients increase near the tourniquet cuff edges.
Nerve injury: preventive measures
Because tourniquet-related nerve injury has been linked to mechanical rather than ischemic factors, mechanical stress merits the most focus for preventing nerve injury. It is now recommended as a best practice that the minimum tourniquet pressure level that is necessary to obtain a stable, bloodless field for the duration of a surgical procedure be employed in all circumstances. This can best be accomplished by using a personalized tourniquet system that applies a tourniquet pressure level based on each individual patient’s Limb Occlusion Pressure (LOP), and that employs personalized tourniquet cuffs designed to minimize cuff pressure gradients and to match the individual patient’s limb size and shape. Limb Occlusion Pressure can be 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, to stop the flow of arterial blood into the limb distal to the cuff. Click here to learn more about Limb Occlusion Pressure, tourniquet cuff design and pressure gradients. Thus, the risk of pressure-related nerve injuries can be reduced by setting the tourniquet pressure level based on Limb Occlusion Pressure, and by employing a tourniquet cuff that applies a low pressure gradient to the underlying limb and that is matched to the patient’s underlying limb size and shape.
Safety measures to prevent nerve injury and pressure-induced complications can be summarized as follows:
- Be sure that the tourniquet instrument and tourniquet cuff have been thoroughly inspected prior to use, according to established guidelines and manufacturer instructions. Click here for information on inspecting tourniquet instruments and cuffs. Make sure that the pressure display accurately reflects the pressure level within the cuff bladder. Some nerve injuries have been shown to be secondary to faulty pressure displays, resulting in the application of excessive tourniquet pressure levels.
- Ensure that a tourniquet cuff is selected to match the limb size and shape at the desired cuff location,and that the selected cuff is snugly and properly applied.
- Use a limb protection sleeve that matches the selected cuff to help prevent wrinkling, pinching and injury to skin and subcutaneous tissues underlying the cuff. Click here to find out more about matching limb protection sleeves.
- Use a personalized tourniquet pressure based on the minimum pressure required to stop blood flow for each individual patient (Limb Occlusion Pressure).
- Minimize tourniquet time.
- Be aware of related safety considerations prior to tourniquet use, during tourniquet use and after tourniquet use.
2. Post-Tourniquet Syndrome
Post-tourniquet syndrome is manifested by pronounced and, at times, prolonged postoperative swelling of the extremity. Approximately half of all post-tourniquet swelling is caused by blood returning to the limb after the release of the tourniquet (hyperemia). The remainder is the result of post-ischemic reactive hyperemia, an additional increase of blood to restore normal acid-base balance in tissue. Post-ischemic reactive hyperemia reflects the body’s attempt to cleanse the limb of the metabolic products of anoxia. Later, additional swelling due to edema or a postoperative hematoma may occur. Prolonged bleeding from the surgical wound also significantly affects swelling. Post-tourniquet syndrome is characterized by edema, stiffness, pallor, weakness without paralysis, and subjective numbness without objective anesthesia.
Post-tourniquet syndrome: mechanism
Unlike nerve palsies, post-tourniquet syndrome is thought to be primarily due to prolonged ischemia rather than the direct mechanical effect of the tourniquet cuff on muscle. Thus, the tourniquet cuff may induce neuromuscular injury by causing ischemia in the tissues distal to the tourniquet cuff, and by compression and ischemia in tissues beneath the tourniquet cuff.
Postoperative weakness, edema, stiffness, dysesthesia, and pain may be falsely attributed to surgical trauma or to lack of patient motivation if the clinician does not have an adequate index of suspicion of tourniquet-related neuromuscular injury. Randomized, prospective studies have demonstrated EMG abnormalities in extremities treated with a routine pneumatic tourniquet. These neurophysiologic changes may be associated with weakness of the involved extremity and a longer clinical recovery time; in fact, postoperative EMG abnormalities may persist as long as 5 months in some cases.
Recent experimental studies suggest that the magnitude of skeletal muscle injury beneath the tourniquet cuff is related to a complex interaction of the cuff pressure level and duration of pressure application.
This complication may occur in patients who have had a tourniquet applied for a prolonged period of time and also in patients when the tourniquet cuff pressure level was insufficient, allowing some arterial inflow while blocking venous outflow for a prolonged time period. Under-pressurization of the tourniquet cuff is a particular risk for elderly patients who frequently have extensive calcification of the major arteries, which renders the vessels less compliant, or non-compliant, to ‘standard’ non-personalized tourniquet pressure levels. Rheumatoid arthritis patients on steroid treatment may experience the same problem in which a bloodless field cannot readily be obtained because of steroid-induced vascular calcification. Because of the significance of postoperative bleeding, patients with prolonged clotting times also are at risk for post-tourniquet syndrome.
Post-tourniquet syndrome: preventive measures
Preventive measures for post tourniquet syndrome are similar to those for nerve injury. During the preoperative assessment, the patient’s physiological status should be reviewed, including:
- Medication history. A patient’s drug history should detect the routine ingestion of any drug that will influence clotting time or promote development of atherosclerotic vascular disease. Among these are steroids, aspirin, and birth control substances.
- History of hypertension.
- Clotting time.
- History of past thromboembolic occurrences.
- Evidence of arterial calcification.
Attempt to minimize tourniquet time and to comply with any recommended tourniquet time limit. A higher than normal tourniquet pressure level may be required, particularly in larger limbs, and it is particularly important with at-risk patients to measure the individual patient’s Limb Occlusion Pressure (LOP) and to set a personalized tourniquet pressure level based on LOP. Note that it is no longer a best practice to set tourniquet pressure levels at high ‘standard’ levels such as 300-350 mmHg for the thigh and 250-300 mmHg for the arm and lower leg, and it is no longer a best practice to set tourniquet pressure level based on systolic blood pressure.
3. Intraoperative Bleeding
Intraoperative bleeding: mechanism
Intraoperative bleeding may be caused by:
- An under-pressurized tourniquet cuff. Under-pressurization of the tourniquet cuff can result in venous pooling, leading to passive venous congestion of the limb, hemorrhagic infiltration of the nerve, and oozing of blood into the surgical field.
- Blood remaining in the limb because of insufficient exsanguination.
- Excessively slow pressurization and depressurization, both of which allow arterial flow to enter the limb distal to the cuff while preventing venous return during the pressurization/depressurization period.
- Improper selection of the tourniquet cuff, resulting in a poor or loose fit of the cuff shape and size to the patient’s limb shape and size.
- Excessive padding between the cuff and the limb, which may prevent a snug cuff-limb fit from proximal to distal edge, and circumferentially.
- A cuff that is applied too loosely.
- Blood entering through the intramedullary nutrient vessels of the long bones (such as the humerus). Theoretically, if breakthrough arterial bleeding does occur, it does so less often than the venous ooze due to medullary cavity bypass of venous blood.
Intraoperative bleeding: preventive measures
To prevent intraoperative bleeding, it is a best practice to select a tourniquet cuff having a size, shape and design that is best matched to the patient and procedure. If additional limb protection is to be used, then a limb protection sleeve matched to the selected cuff should be used rather than stockinette or padding. After snug application of the selected tourniquet cuff, the patient’s Limb Occlusion Pressure (LOP) should be measured, and tourniquet pressure level should be set based on the LOP, according to established guidelines or manufacturer’s instructions. If at some time during a surgical procedure the tourniquet cuff pressure level selected is insufficient to stop arterial bleeding into the operative field, the tourniquet pressure level may be increased in increments of 25 mmHg until a satisfactory bloodless field is re-established. Some surgeons may prefer to deflate the cuff, re-exsanguinate the limb, and re-inflate to a higher pressure level in order to prevent the blood from being trapped in the distal part of the extremity.
4. Compartment Pressure Syndrome
Compartment syndrome is a condition in which external and internal pressures on a confined space result in swelling of the extremity. It is a relatively rare but potentially serious complication of tourniquet use. The compartment is the area between the two tough fascia layers of a muscle group. An infinitesimal amount of fluid in the space normally allows contraction and relaxation of the muscle group within its covering fascia. There is no room for additional fluid. The first symptom of compartment syndrome is usually pain that increases in severity and cannot be alleviated by narcotics. Other symptoms include muscle weakness, paresthesia, decreased or absent pulses, tense skin over the limb and, in some cases, irreversible paralysis.
Compartment pressure syndrome: mechanism
The combination of external compression and an increase in compartment contents due to either trauma or surgery may cause a compartment syndrome. Like post-tourniquet syndrome, this complication is due to tourniquet ischemia time. Prolonged tourniquet times lead to a fall in tissue pH, an increase in capillary permeability, and a prolongation of clotting, all of which promote the development of a compartment syndrome.
Patients at risk for tourniquet-related compartment syndrome are those with a previous history of compartment syndrome symptoms. Patients with McArdle’s disease (a muscle phosphorylase deficiency disease) exhibit compartment-like syndromes after about 20 minutes of vigorous exercise. Use of a pneumatic tourniquet on these patients, even for a short time, may lead to compartment syndrome.
Also at risk are patients who must have a cast placed on a limb prior to tourniquet release. Post-tourniquet swelling, if inhibited by a cast, can lead to compartment syndrome.
Compartment pressure syndrome: preventive measures
The following are preventive measures for compartment syndrome:
- Preoperative evaluation of the patient’s personal and family history should be carried out to look for any previous compartment syndrome-like symptoms; patients with McArdle’s disease are contraindicated.
- Tourniquet time should be minimized.
Solid cast placement should be avoided prior to tourniquet cuff depressurization.
5. Injuries to Skin and Subcutaneous Tissues
Pressure-related injuries to skin and subcutaneous tissues, including bruising and petechiae, as well as chemical injuries to skin and subcutaneous tissues underlying the cuff site are uncommon consequences of pneumatic tourniquet use; however, when they do occur, they may cause considerable patient discomfort and distress. Although occasionally seen in adults, chemical injuries caused by prep solutions accumulating beneath the cuff occur most frequently in the sensitive skin and soft tissues of children. Tourniquet cuffs may cause pressure-related damage to skin and subcutaneous tissues due to shearing stresses and uneven application of pressure to the underlying limb by the pressurized cuff. This tends to begin upon cuff pressurization and continue throughout the procedure, and may be a particular problem in older patients with delicate skin and subcutaneous tissues. Clinical experience has shown that such injuries occur with and without fluid accumulation under the cuff and can be attributed to cuff design, cuff application, fluid leakage, excessive tourniquet pressure level, excessive tourniquet duration, uneven application of cuff pressure to the underlying limb, manual readjustment or rotation of the cuff around the limb after application, or a combination of these factors. In one case report severe friction burns were caused by a thigh cuff sliding distally off the underlying padding during the procedure.
Injuries to skin and subcutaneous tissues: mechanism
Pressure-related skin injuries and chemical injuries are the result of skin breakdown, friction, or folding, wrinkling or pinching of skin and subcutaneous tissues underlying the tourniquet cuff. Pressure-related skin and soft-tissue injuries may be due to inadequate limb protection between the cuff and limb, or faulty cuff application, in patients with loose or thin skin such as obese patients, or in elderly patients with loose, flabby skin. Patients with compromised circulation, such as those who are elderly or diabetic, are also at higher risk for pressure-related injuries to skin and underlying soft tissues.
Chemical injuries are most often caused by antimicrobial prep solutions penetrating beneath the tourniquet cuff and accumulating there. When the cuff is pressurized, the accumulated prep solution is pressed tightly against the patient’s skin underlying the cuff. Chemical injuries are more likely to occur when prep solutions come in contact with the more delicate skin of young children.
Injuries to skin and subcutaneous tissues: preventive measures
The following measures will help prevent injuries to skin and subcutaneous tissues:
- Use adhesive tape or an adhesive edged drape between the distal edge of the cuff and limb to prevent prep solution from leaking under the tourniquet; this also helps keep the cuff free from stains.
- Position the cuff properly on the limb. Apply the cuff high on the limb and away from the joints; applying the cuff near bony joints prevents a proper fit, resulting in uneven pressure distribution on the limb, affects compression of underlying blood vessels, and may produce high pressure gradients.
- Use the correct limb protection technique as recommended for the selected cuff. If available, use a limb protection sleeve specifically designed to match the selected cuff. This will provide light compression and give a toning effect to loose skin without blocking venous return, will reduce the tendency of the cuff to gather up, shear, wrinkle and pinch loose skin and subcutaneous tissue. It is no longer considered to be best practice to use cast padding or unmatched stockinette beneath the cuff.
- For better cuff placement on the obese patient, draw the subcutaneous tissue and skin distally before applying the tourniquet. After the tissue is released, it will help hold the cuff in place.
- Do not readjust or rotate an already positioned tourniquet cuff. Rotation produces shearing forces which may damage the underlying tissues. If repositioning is necessary, the cuff should be removed and re-applied.
6. Digital Necrosis
Digital necrosis is the gangrenous destruction of a finger or toe as a result of prolonged ischemia/anoxia.
Digital necrosis: mechanism
The common practice of using a Penrose drain, rubber band, or a rolled finger of the surgical glove as a tourniquet is associated with this complication. Causes of digital necrosis are:
- Excessive, uncontrolled pressure. This is a major hazard associated with all non-pneumatic tourniquets.
- Failure to remove the constricting device. This is more prevalent when rubber bands or Penrose drains are used, since they can be easily overlooked.
- Prolonged tourniquet time.
Patients at increased risk include those with impaired circulation (i.e., Raynaud’s syndrome, peripheral vascular disease, diabetes, etc.), those with small limbs, and the elderly.
Digital necrosis: preventive measures
Digital necrosis can be prevented by taking the following safety measures:
- Eliminate excessive, uncontrolled pressure from the constricting device by using a modern tourniquet instrument and setting a tourniquet pressure level based on the patient’s Limb Occlusion Pressure. Click here to learn more about Limb Occlusion Pressure.
- Adhere strictly to a predetermined tourniquet time.
7. Toxic Reactions
Toxic reactions to local anesthetic agents are potential complications of Intravenous Regional Anesthesia (IVRA, also called Bier block anesthesia). Hypersensitive patients can exhibit generalized symptoms almost immediately. The greatest danger is an inadvertent bolus of local anesthetic entering the general circulation, which can affect the central nervous system and the heart. Early recognition and prompt treatment of early signs of toxicity such as dizziness, drowsiness, respiratory depression, tinnitus, and bradycardia may prevent progression to more serious complications, like grand mal seizures, coma, cardiorespiratory depression, and even cardiac arrest and death. Click here to learn more about Intravenous Regional Anesthesia (IVRA).
Toxic reactions: mechanism
The major cause of adverse effects of IVRA and/or failure of the technique is technical error. A toxic reaction may result from:
- Under-pressurization of the tourniquet cuff prior to injection of the anesthetic agent, and during the procedure. If complete occlusion is not present, leakage of the anesthetic agent may occur underneath the cuff and into systemic circulation.
- Inadequate exsanguination prior to injection of the local anesthetic agent. If the veins distal to the tourniquet cuff are not properly exsanguinated, then injection of the anesthetic agent into those veins may increase venous pressure to a level sufficient to allow the injected agent to flow beneath the cuff and into systemic circulation.
- Accidental, sudden deflation of the tourniquet after the anesthetic agent has been injected.
- Deflation of the tourniquet too soon after injection of local anesthetic; prior to tourniquet release: approximately 15-20 minutes is required for satisfactory tissue binding of the local anesthetic, thus removing the anesthetic from the circulatory system.
In general, high-risk patients may have a hypersensitivity to the anesthetic agent, a condition that makes arterial occlusion difficult (i.e., obesity, hypertension, arterial calcification, etc.), a chronic respiratory disease (e.g., chronic obstructive pulmonary disease); congestive heart failure; or CNS impairments (e.g., seizure disorders). Many of these problems are associated with advanced age; thus, elderly patients with any of these conditions are at higher risk.
One study found detectable levels of anesthetic agent in the general circulation even while the tourniquet was properly inflated. The authors suggested that the hemodynamics in the skeleton allowed endosteal (intraosseous, medullary) venous outflow from the extremity, using the bone as a tourniquet bypass while the tourniquet still effectively blocked extraosseous arterial inflow and venous return. Thus, venous blood from the extremity slowly entered the general circulation through this intraosseous skeletal bypass.
Toxic reactions: preventive measures
The following preventive measures will reduce the possibility of toxic reactions:
- Obtain a complete allergy history when IVRA is being contemplated. Of particular note is any allergic reaction to any local anesthetic agent used for dental work or another surgical procedure. Persons who have contact, inhalation, and/or food allergies are also suspect because of their hypersensitivity. Such an immunological hypersensitivity may preclude the use of IVRA unless other physical conditions rule out general anesthesia.
- Obtain a complete medical history to detect the presence of cardiopulmonary or renal disease, seizure disorders, vascular problems, morbid obesity, diabetes, and the like. The severity of such problems may eliminate administration of a general anesthetic and make IVRA the better of two poor choices.
- Select a tourniquet instrument that includes additional safety features specifically for IVRA, such as a safety interlock to help prevent inadvertent depressurization of both cuff bladders, thus preventing inadvertent and premature flow of local anesthetic agent into systemic circulation.
- Select a dual-bladder tourniquet cuff for IVRA. Use a personalized dual-bladder tourniquet cuff designed to minimize cuff pressure gradients and to match the individual patient’s limb size and shape.
- Test the tourniquet instrument and cuff thoroughly before each use, in accordance with established guidelines and manufacturer instructions.
- Exsanguinate the limb distal to the tourniquet cuff site thoroughly before cuff pressurization and before injection of the local anesthetic agent.
- Ensure that the bloodflow into limb distal to the cuff is occluded at the selected cuff pressure level by confirming absence of a distal arterial pulse. Limb Occlusion Pressure (LOP) is particularly useful in setting the cuff pressure levels in IVRA procedures due to the importance of establishing and maintaining occlusion, and due to the fact that higher tourniquet pressure levels may be required due to the use of dual-bladder cuffs with narrower bladders.
- Observe the patient’s physiological status at all times for any sign or symptom of a toxic reaction, beginning immediately after injection of the local anesthetic agent.
- Follow established guidelines and best practices regarding inflation and deflation of each bladder of the dual-bladder tourniquet cuff during the surgical procedure, and at the end of the procedure.
Deep venous thrombosis and the associated risk of pulmonary embolism are a major cause of morbidity and mortality in lower extremity orthopaedic surgery and have led to the use of various prevention modalities. Lower extremity deep venous thrombosis has been identified at autopsy as the source of pulmonary embolism in several cases of tourniquet-related cardiac arrest. Less severe episodes of venous embolism during surgery using tourniquets may not be recognized by simple clinical observation.
Thrombosis: preventive measures
To prevent dislodgement of thrombi, do not use an elastic bandage for exsanguination in a patient with a traumatic injury or in a patient who recently has been in a cast. Some experts recommend sub-therapeutic heparinization prior to the inflation of the tourniquet. Do not use a rolling elastic ring for exsanguination of any patient.
9. Other Complications
Other complications of pneumatic tourniquet use might include:
Tourniquet pain is the most common complication seen in clinical practice. Hypertension and a dull, aching pain (tourniquet pain) throughout the limb may develop during and following tourniquet use, despite otherwise adequate anesthesia. The initial sensation of pressure at the tourniquet site may be replaced by a progressive numbness and paralysis, and in extreme cases may progress to complete paralysis. Click here learn more about tourniquet-related nerve injury. A severe, aching sensation at the site of the tourniquet or distal extremity may progressively develop. After depressurization of the tourniquet cuff, a different pain sensation may be noted, associated with reperfusion of the limb. This sensation is described as being equal to or greater than the intensity of the discomfort caused by the tourniquet cuff immediately before depressurization. The average time of pain tolerance after pressurization of the tourniquet cuff has been reported to be about 30 minutes in un-sedated patients.
Heat generated by surgical lights or powered surgical instruments is not dissipated in limbs under tourniquet control, and tissue may be subject to drying or trauma. Frequent irrigation, special draping, and low-power surgical lights are recommended to reduce the risk of thermal damage to tissues.
Limb tourniquets have been associated with a progressive increase in central body temperature in pediatric patients, and the increase is significantly greater when bilateral tourniquets are used. It has been suggested that pediatric patients requiring intraoperative tourniquets should not be aggressively warmed during surgery.
Rhabdomyolysis has been described as a rare complication of prolonged ischemia resulting from prolonged tourniquet time in some patients. It is defined as the release of the cellular contents after damage to skeletal muscle and has a variable clinical presentation. Pyrexia and tachycardia develop, and affected patients may complain of pain, tenderness, edema, and hemorrhage of the limb. Classically, the urine is dark and oliguria may develop. Reduced tourniquet times have greatly reduced the incidence of rhabdomyolysis in recent years. Prompt recognition and early treatment prevent long term sequelae.
While the tourniquet is pressurized, metabolic changes occur in the ischemic limb, changes that include increased PaCO2, lactic acid, and potassium, and decreased levels of PaO2 and pH. Pathophysiologic changes due to pressure, hypoxia, hypercarbia, and acidosis of the tissue occur and become significant after about 90 minutes of tourniquet use.
Deflation of the tourniquet results in the release of these products of ischemia into the general circulation. The resultant decreases in arterial pH and PaO2 and increases in arterial lactic acid, potassium, PaCO2 and end tidal carbon dioxide are associated with significant decreases in mean arterial and central venous pressures and increases in heart rate. The clinical significance of these changes, if any, is not yet clear; in healthy individuals, no significant adverse effects have been observed. It has been hypothesized that a rapid increase in PaCO2 after thigh tourniquet release may result in a corresponding increase in cerebral blood flow (CBF), which may be hazardous in patients with increased intracranial pressure. Although this risk is hypothetical, it may be prudent to monitor the CO2 level in any such at-risk patient and treat any increase promptly by hyperventilation.
Metabolic changes are generally more pronounced when bilateral tourniquets are used, and so it has been hypothesized that the risk of Fat Embolism Syndrome (FES) upon release of the tourniquet pressure in procedures such as bilateral total knee arthroplasty may be reduced if deflation times are separated by 30-45 minutes.