Optimization of surgical tourniquet usage to improve patient outcomes: Translational cross-disciplinary implications of a surgical practice survey.

Tourniquet use is common practice in many millions of orthopaedic procedures annually. Recent reviews of risks and benefits of surgical tourniquet use have primarily involved meta-analyses, many of which have forgone a comprehensive risk-benefit analysis to simply question whether "tourniquet or no tourniquet" use produces improved patient outcomes, often leading to limited, inconclusive, or conflicting results. To investigate further, a pilot survey was undertaken to determine current practices, opinions, and understandings among orthopaedic surgeons in Canada regarding use of surgical tourniquets in total knee arthroplasties (TKAs). Results of the pilot survey showed a wide range of understanding and practice associated with tourniquet use in TKAs, especially regarding tourniquet pressures and tourniquet times, two key factors known from basic research and clinical studies to impact the safety and efficacy of tourniquet use. The wide variation of use indicated by the survey results reveals important implications for surgeons, researchers, educators, and biomedical engineers, to better understand the association between key tourniquet parameters and outcomes assessed in research, which may be factors leading to their often limited, inconclusive, and conflicting results. Lastly, we provide an overview of the overly simplified assessments of tourniquet use in meta-analyses, whose conclusions may not provide an understanding of how or whether key tourniquet parameters might be optimized to retain the benefits of tourniquet use while mitigating the associated real or perceived risks.

Tourniquet-induced nerve compression injuries are caused by high pressure levels and gradients - a review of the evidence to guide safe surgical, pre-hospital and blood flow restriction usage.

Tourniquets in orthopaedic surgery safely provide blood free surgical fields, but their use is not without risk. Tourniquets can result in temporary or permanent injury to underlying nerves, muscles, blood vessels and soft tissues. Advances in safety, accuracy and reliability of surgical tourniquet systems have reduced nerve-related injuries by reducing pressure levels and pressure gradients, but that may have resulted in reduced awareness of potential injury mechanisms. Short-term use of pre-hospital tourniquets is effective in preventing life-threatening blood loss, but a better understanding of the differences between tourniquets designed for pre-hospital vs surgical use will provide a framework around which to develop guidelines for admitting to hospital individuals with pre-applied tourniquets. Recent evidence supports the application of tourniquets for blood flow restriction (BFR) therapy to reduce muscular atrophy, increase muscle strength, and stimulate bone growth. BFR therapy when appropriately prescribed can augment a surgeon's treatment plan, improving patient outcomes and reducing recovery time. Key risks, hazards, and mechanisms of injury for surgical, BFR therapy, and pre-hospital tourniquet use are identified, and a description is given of how advances in personalized tourniquet systems have reduced tourniquet-related injuries in these broader settings, increasing patient safety and how these advances are improving treatment outcomes.

Deep venous thrombosis identification from analysis of ultrasound data.

PURPOSE: The purpose of this research was to determine whether combined ultrasound- and sensor-based compressibility and augmented blood flow measures yielded better results for DVT detection than for the individual measures alone. METHODS: Twenty-six limbs from 19 patients were scanned using a sensorized ultrasound DVT screening system, and compressibility and flow measures were obtained at 125 locations. Results from conventional compression ultrasound examination were used as gold standard, with seven vessels (four patients) positive for DVT. A classification approach was used to combine the individual DVT measures per vessel and generate an optimal feature for every possible combination of individual measures. Sensitivity and specificity were calculated for the individual measures and for all combined measures, as was a usefulness criteria [Formula: see text] for measuring class separability. RESULTS: Seven optimal combined features were found with 100% sensitivity and 100% specificity, with the best combined feature having a [Formula: see text] value over two orders of magnitude greater than the best individual DVT measure. CONCLUSIONS: The proposed approach for DVT detection combines different aspects of thrombus detection in a novel way generating a quantifiable measure and outperforms any of the individual measures when used independently. All of the combined measures included the flow measure as well as the slope compressibility measure, which uses the magnitude of the force applied by the ultrasound probe, suggesting that these measurements provide important information when characterizing DVT.

Surgical tourniquets in orthopaedics.

Higher levels of tourniquet pressure and higher pressure gradients beneath tourniquet cuffs are associated with a higher risk of nerve-related injury. Measurement of limb occlusion pressure can help to minimize tourniquet pressure levels and pressure gradients for individual patients and individual surgical procedures. Selective use of pneumatic, wider, and contoured tourniquet cuffs reduces tourniquet pressure levels and the applied pressure gradients.

Minimizing tourniquet pressure in pediatric anterior cruciate ligament reconstructive surgery: a blinded, prospective randomized controlled trial.

BACKGROUND: Tourniquet cuff pressures in pediatric patients are commonly set at standard pressures. Recent evidence on adult subjects has shown that safer and more effective cuff pressures can be achieved by measuring limb occlusion pressure (LOP) and using a wide contour cuff. There is little evidence validating these techniques in children. The primary objective of this study was to evaluate if a difference in tourniquet cuff pressure can be achieved in a pediatric population using a wide contour cuff in conjunction with measured LOP when compared with a standard cuff and pressure. METHODS: Subjects aged 10 to 17 years that underwent anterior cruciate ligament repair were included and randomized into either the control group or the experimental LOP group using variable block randomization. The tourniquet cuff was inflated to 300 mm Hg in the control group or to the recommended tourniquet pressure based on LOP measurement in the LOP group. The surgeon was blinded to cuff selection, application, and pressure throughout the surgical procedure. Immediately after the surgical procedure, the surgeon rated the quality of the bloodless field on a visual analog scale. This study was powered as an effectiveness trial, and intention to treat analysis was used. RESULTS: After a planned interim analysis at midpoint, complete data were recorded for 11 (control group) and 10 (LOP group) patients. The quality of the surgical field was not different between the groups (P = 0.053). There was a statistically significant difference in the mean cuff pressure between the control (300 mm Hg) and the LOP (151 mm Hg) groups (P < 0.001). We ran the same analysis comparing the LOP data with the hypothetical control data of 250 mm Hg, and our results remained statistically significant (P < 0.001). CONCLUSIONS: The use of an automatic LOP measurement with the use of wide contour cuffs can significantly reduce mean tourniquet cuff pressures in pediatric patients compared with the typical practice of 300 or 250 mm Hg without compromising the quality of the surgical field. LEVEL OF EVIDENCE: Level 1, prospective randomized controlled trial.

Real-time vessel segmentation and tracking for ultrasound imaging applications.

A method for vessel segmentation and tracking in ultrasound images using Kalman filters is presented. A modified Star-Kalman algorithm is used to determine vessel contours and ellipse parameters using an extended Kalman filter with an elliptical model. The parameters can be used to easily calculate the transverse vessel area which is of clinical use. A temporal Kalman filter is used for tracking the vessel center over several frames, using location measurements from a handheld sensorized ultrasound probe. The segmentation and tracking have been implemented in real-time and validated using simulated ultrasound data with known features and real data, for which expert segmentation was performed. Results indicate that mean errors between segmented contours and expert tracings are on the order of 1%-2% of the maximum feature dimension, and that the transverse cross-sectional vessel area as computed from estimated ellipse parameters a, b as determined by our algorithm is within 10% of that determined by experts. The location of the vessel center was tracked accurately for a range of speeds from 1.4 to 11.2 mm/s.

System for deep venous thrombosis detection using objective compression measures.

A system for objective vessel compression assessment for deep venous thrombosis characterization using ultrasound image data and a sensorized ultrasound probe is presented. Two new objective measures calculated from applied force and transverse vessel area are also presented and used to describe vessel compressibility. A modified star-Kalman algorithm is used for feature detection in acquired ultrasound images, and objective measures of vessel compressibility are calculated from the detected features and acquired force and location data from the sensorized probe. A three-dimensional shape model of the examined vessel that includes compressibility measures mapped as colors to its surface is presented on the user interface, as well as a virtual representation of the image plane. The compressibility measures were validated using expert segmentation of healthy and diseased vessels and compared using paired t-tests, which showed a significant difference between healthy and diseased cases for both measures. 100% sensitivity and specificity were obtained for both measures. The system was implemented in real-time (16 Hz) and evaluated using a tissue phantom and on healthy human subjects. Sensitivity was 100% and 60%, while specificity was 97% for both measures when implemented. The initial results for the system and its components are promising.

Survey of tourniquet use in orthopaedic foot and ankle surgery.

BACKGROUND: Tourniquet technique varies among foot and ankle surgeons, and to establish a standard practice guideline the current standard of care should be examined. METHODS: One hundred and forty responses were received after 253 surveys were mailed to American Orthopaedic Foot and Ankle Society (AOFAS) members, concerning type of tourniquets, location, and pressures used. RESULTS: Cuff pressures most commonly used were 301 to 350 mmHg for thigh cuffs (49% of thigh cuff users) and 201 to 250 mmHG for calf and ankle cuffs (52% of calf cuff users, 66% of ankle cuff users). A substantial number of foot and ankle surgeons who use calf and ankle cuffs frequently use pressures above 250 mmHg (41% of calf cuff users, 19% of ankle cuff users). Only 9% use limb occlusion pressure when determining cuff pressure. CONCLUSION: Based on the existing evidence-based literature these pressures may be higher than necessary for many patients, and increased adoption of optimal pressure setting techniques as reported in the literature may help reduce tourniquet pressures used and risk of tourniquet injury. Respondents reported experiencing or hearing reports of breakthrough bleeding, nerve injury, and skin injuries under the cuff.

Wide contoured thigh cuffs and automated limb occlusion measurement allow lower tourniquet pressures.

We examined the amount of thigh tourniquet pressure that can be reduced from the typical 300 to 350 mm Hg by using a new automated plethysmographic limb occlusion pressure measurement technique. We also examined how much pressure could be reduced by using a wide contoured cuff compared with a standard cuff and if limb occlusion and systolic blood pressures were well correlated. Patients having surgery with a thigh tourniquet were randomized into two groups, one group having surgery with a standard cuff and the other with a wide cuff. Pressure was set at the automatically measured limb occlusion pressure plus a safety margin. Systolic blood pressure and quality of the bloodless field were recorded. The standard cuff maintained an acceptable bloodless field for 18 of 20 patients at an average pressure of 242 mm Hg, and the wide cuff was acceptable for 19 of 20 patients at an average of 202 mm Hg. One patient in each group had a poor bloodless surgical field at the initial pressure, and one patient in each group had a poor bloodless surgical field after a sharp rise in blood pressure during surgery. Systolic blood pressure was not correlated well enough to limb occlusion pressure to be used alone to set the optimum cuff pressure. The automated limb occlusion pressure technique and the wide contoured cuff reduced average pressure by 33-42% from typical pressures.

Can a new design of pneumatic compression device reduce variations in delivered therapy for the mechanical prophylaxis of thromboembolic disease after total hip arthroplasty?

BACKGROUND: Compression devices have been shown to prevent thromboembolic disease. However, the pressures generated may not be the same as the ones recommended by the manufacturer. The purpose of this study is to investigate a new sequential compression device with feedback to maintain optimal therapy, and to determine whether therapy is improved with this new device. PATIENTS AND METHOD: A series of 50 patients undergoing elective total hip arthroplasty at a major tertiary-care hospital with a special interest in joint replacement were enrolled prospectively. In addition to pharmacological prophylaxis for thromboembolic disease, all patients received compression from a modified device. Maximum pressures generated and the rate of pressure rise in each of the 3 compartments within the device sleeves were measured and the results compared with data from historical controls. RESULTS: We considered therapy to be ideal when in a particular compression cycle all chambers of both right and left sleeves reach within 10% of their target pressures at within 10% of their target pressure rise rates. The average patient received this ideal therapy 88% of the time that the new trial sequential compression device was operating. This represents a dramatic improvement over previous devices. CONCLUSIONS: The new device allows dramatically improved pressures within the device because of a feedback loop that allows dynamic control of each chamber's pressure. Improved consistency of delivery should make it easier to accurately assess the true benefits of mechanical prophylaxis with a sequential compression device.

Survey of tourniquet use in podiatric surgery.

Tourniquet use in foot and ankle surgery is common practice; however, the technique varies among foot and ankle surgeons and there are no standard guidelines. To analyze trends in foot and ankle tourniquet use, the authors conducted an e-mail survey. One thousand six hundred sixty-five foot and ankle surgeons were sent a tourniquet-use survey via e-mail, across Canada and the United States. Nineteen percent of the recipients completed and returned the surveys. Eleven (3.4%) rarely or never use a tourniquet and 8 (2.5%) use an Esmarch bandage tourniquet at the ankle. Most use pneumatic ankle cuffs (92% use, 27% use exclusively); many also use thigh cuffs (69%) and some also use calf cuffs (15%). Most thigh-cuff users (62%) experience problems with cuff fit sometimes or often. All but 3 respondents exsanguinate the limb before tourniquet inflation. Specific devices used for exsanguination varied among surgeons. Most commonly used tourniquet pressures range from /=351 mm Hg for the thigh (64% use pressures between 301 and 350 mm Hg). Only 7% of respondents consider limb occlusion pressure when selecting tourniquet cuff pressure. Based on published studies of limb occlusion pressures, these ranges suggest that some of the more common pressure settings may be higher than necessary for many patients. Vascular disease or previous bypass (91%) and deep vein thrombosis (83%) were the most commonly listed contraindications to tourniquet use. Approximately 10% of respondents have either experienced or learned of skin and nerve injuries secondary to lower extremity tourniquet use at any level. The varied responses show a lack of overall consensus on tourniquet pressure settings. Guidelines for optimizing cuff pressure and technique should be established to minimize the risk of complications.

Tourniquet safety in lower leg applications.

PURPOSE: To reduce the chance of injury due to pneumatic tourniquet use, the minimum cuff pressure required to maintain a bloodless field should be used. The purpose of this study was to find out if Limb Occlusion Pressure (LOP--the cuff pressure required to occlude arterial flow) is lower with a wide contoured cuff than with a standard width cylindrical cuff at the calf, if cuff pressures based on measured LOP will be lower than the typical 250 mmHg used in lower leg cuffs, and if a new automatic LOP measurement method gives the same results as the standard Doppler stethoscope method. SAMPLE: 16 adult volunteers were tested in a controlled laboratory setting, and 53 clinical cases were reviewed at two centers. DESIGN: Repeated measures comparison of LOP on volunteers with the two different cuffs and measurement methods, and review of clinical cases. RESULTS: LOP was lower with the wide cuff on all volunteers (mean reduction 20 mmHg, SD 8.6, range 5-35, p < 0.001). The average difference of 1.2 mmHg between Doppler and automatic LOP readings was not significant (p = 0.43). Based on the volunteer results, using LOP plus a safety margin of 40, 60, or 80 mmHg (for LOP < 130, 131-190, or 190+ respectively) with a standard width cylindrical cuff will lead to an average cuff pressure of 223 mmHg (range 170-299, SD 36), 11% lower than typical practice and up to 80 mmHg (32%) lower on some patients. Using a wide, contoured cuff should further reduce cuff pressures to an average of 195 mmHg (range 160-280, SD 33), 22% lower than typical practice and a reduction of up to 90 mmHg (36%). At two clinics, the wide cuff maintained a bloodless field in 48 out of 53 cases (91%) when used at 200 mmHg. CONCLUSIONS: Using a wide, contoured cuff at the calf should reduce required cuff pressures compared to a standard cuff. Setting cuff pressure based on LOP should further reduce cuff pressures for most patients compared to typically used pressures. With continued development, the new automatic method may become a viable alternative to the Doppler method and may make LOP measurement more practical in the clinical setting.