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.

Black carbon particulate matter emission factors for buoyancy-driven associated gas flares.

Flaring is a technique used extensively in the oil and gas industry to burn unwanted flammable gases. Oxidation of the gas can preclude emissions of methane (a potent greenhouse gas); however, flaring creates other pollutant emissions such as particulate matter (PM) in the form of soot or black carbon (BC). Currently available PM emissionfactors for flares were reviewed and found to be questionably accurate, or based on measurements not directly relevant to open-atmosphere flares. In addition, most previous studies of soot emissions from turbulent diffusion flames considered alkene or alkyne based gaseous fuels, and few considered mixed fuels in detail and/or lower sooting propensity fuels such as methane, which is the predominant constituent of gas flared in the upstream oil and gas industry. Quantitative emission measurements were performed on laboratory-scale flares for a range of burner diameters, exit velocities, and fuel compositions. Drawing from established standards, a sampling protocol was developed that employed both gravimetric analysis of filter samples and real-time measurements of soot volume fraction using a laser-induced incandescence (LII) system. For the full range of conditions tested (burner inner diameter [ID] of 12.7-76.2 mm, exit velocity 0.1-2.2 m/sec, 4- and 6-component methane-based fuel mixtures representative of associated gas in the upstream oil industry), measured soot emission factors were less than 0.84 kg soot/10(3) m3 fuel. A simple empirical relationship is presented to estimate the PM emission factor as a function of the fuel heating value for a range of conditions, which, although still limited, is an improvement over currently available emission factors.

Investigation of clinically acceptable agreement between two methods of automatic measurement of limb occlusion pressure: a randomised trial.

BACKGROUND: Development of automatic, pneumatic tourniquet technology and use of personalised tourniquet pressures has improved the safety and accuracy of surgical tourniquet systems. Personalisation of tourniquet pressure requires accurate measurement of limb occlusion pressure (LOP), which can be measured automatically through two different methods. The 'embedded LOP' method measures LOP using a dual-purpose tourniquet cuff acting as both patient sensor and pneumatic effector. The 'distal LOP' method measures LOP using a distal sensor applied to the patient's finger or toe of the operating limb, using photoplethysmography to detect volumetric changes in peripheral blood circulation. The distal LOP method has been used clinically for many years; the embedded LOP method was developed recently with several advantages over the distal LOP method. While both methods have clinically acceptable accuracy in comparison to LOP measured using the manual Doppler ultrasound method, these two automatic methods have not been directly compared. The purpose of this study is to investigate if the embedded and distal methods of LOP measurement have clinically acceptable agreement. The differences in pairs of LOP measurement in the upper and lower limbs of 81 healthy individuals were compared using modified Bland and Altman analysis. In surgery, it is common for cuff pressure to deviate from the pressure setpoint due to limb manipulation. Surgical tourniquet systems utilise a ± 15 mmHg pressure alarm window, whereby if the cuff pressure deviates from the pressure setpoint by > 15 mmHg, an audiovisual alarm is triggered. Therefore, if the difference (bias) ± SE, 95% CI of the bias and SD of differences ± SE in LOP measurement between the embedded and distal methods were all within ±15 mmHg, this would demonstrate that the two methods have clinically acceptable agreement. RESULTS: LOP measurement using the embedded LOP method was - 0.81 ± 0.75 mmHg (bias ± standard error) lower than the distal LOP method. The 95% confidence interval of the bias was - 2.29 to 0.66 mmHg. The standard deviation of the differences ± standard error was 10.35 ± 0.49 mmHg. These results show that the embedded and distal methods of LOP measurement demonstrate clinically acceptable agreement. CONCLUSIONS: The findings of this study demonstrate clinically acceptable agreement between the embedded and distal methods of LOP measurement. The findings support the use of the embedded LOP method of automatic LOP measurement using dual-purpose tourniquet cuffs to enable accurate, effective and simple prescription of personalised tourniquet cuff pressures in a clinical setting.

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.

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.

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.

Does knowledge of cancer diagnosis affect quality of life? A methodological challenge.

BACKGROUND: As part of an assessment of quality of life in lung cancer patients an investigation was carried out to examine whether the knowledge of their diagnosis affected their quality of life. METHODS: Every patient in a defined geographical area with a potential diagnosis of lung cancer was interviewed at first consultation and after a definitive treatment has been given. Quality of life was assessed using three standard measures: the Nottingham Health Profile (NHP), the EORTC quality of life questionnaire (QLQ-C30) and its lung cancer supplementary questionnaire (QLQ-LC13). Comparison was made in quality of life scores between patients who knew their cancer diagnosis and those who did not. RESULTS: In all, 129 lung cancer patients were interviewed. Of these, 30 patients (23%) knew and 99 (78%) did not know their cancer diagnosis at the time of baseline assessment. The patient groups were similar in their characteristics except for age (P = 0.04) and cell type (P < 0.0001). Overall, there were no significant differences between these two groups with regard to their scores on the three instruments used. A major finding was that both group scored almost the same on emotional reactions (P = 0.8) and social isolation (P = 1.0) as measured by the NHP, and emotional (P = 0.7) and social functioning (P = 1.0) as measured by the EORTC QLQ-C30. In addition there were no significant differences in patients' symptom scores between those who knew their diagnosis and those who did not, nor did any consistent pattern emerge. The only significant difference was for sleep difficulties (P = 0.02). CONCLUSION: The findings suggest that the knowledge of cancer diagnosis does not affect the way in which patients respond to quality of life questionnaires.

Quality of life in lung cancer patients: does socioeconomic status matter?

BACKGROUND: As part of a prospective study on quality of life in newly diagnosed lung cancer patients an investigation was carried out to examine whether there were differences among patients' quality of life scores and their socioeconomic status. METHODS: Quality of life was measured at two points in time (baseline and three months after initial treatment) using three standard instruments; the Nottingham Health Profile (NHP), the European Organization for Research and Cancer Treatment Quality of Life Questionnaire (EORTC QLQ-C30) and its lung cancer supplement (QLQ-LC13). Socioeconomic status for each individual patient was derived using Carstairs and Morris Deprivation Category ranging from 1 (least deprived) to 7 (most deprived) on the basis of the postcode sector of their address. RESULTS: In all, 129 lung cancer patients entered into the study. Of these data for 82 patients were complete (at baseline and follow-up). 57% of patients were of lower socioeconomic status and they had more health problems, less functioning, and more symptoms as compared to affluent patients. Of these, physical mobility (P = 0.05), energy (P = 0.01), role functioning (P = 0.04), physical functioning (P = 0.03), and breathlessness (P = 0.02) were significant at baseline. However, at follow-up assessment there was no significant difference between patient groups nor did any consistent pattern emerge. CONCLUSION: At baseline assessment patients of lower socioeconomic status showed lower health related quality of life. Since there was no clear trend at follow-up assessment this suggests that patients from different socioeconomic status responded to treatment similarly. In general, the findings suggest that quality of life is not only the outcome of the disease and its treatment, but is also highly dependent on each patients' socioeconomic characteristics.

Association between course of study at university and cause-specific mortality.

Although socioeconomic position is clearly related to mortality and one measure of this is length of education, it is not known whether the choice of course at university determines future health. We therefore investigated the association between faculty of study and all-cause and cause-specific mortality in a prospective follow-up of male students who underwent health examinations while attending Glasgow University from 1948 to 1968. Among the 9887 (84%) alumni traced by means of the NHS Central Register, 8367 (85%) had full data on important potential confounding variables; 939 of these men had died. Physiological variables differed little between students from the various faculties. Medical students were most likely to come from affluent social backgrounds and, after law students, were most likely to be smokers. Compared with former medical students, former arts and law students had excess all-cause and cardiovascular disease mortality, while science and engineering alumni had similar risks. Former medical students had lower lung cancer mortality than other alumni but higher mortality from alcohol-related causes including accidents, suicide and violence. The lower mortality risks observed among former medical and engineering students may be due to their better employment prospects and healthier lifestyle behaviours, although the high mortality from alcohol-related causes among former medical students underscores the complexity of choice of health behaviour. The findings point to the potential for disease prevention among the large proportion of the population who now have third-level education.

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.

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.

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.

Height in young adulthood and risk of death from cardiorespiratory disease: a prospective study of male former students of Glasgow University, Scotland.

To investigate the association between height in young, socially homogeneous males and cause-specific mortality, the authors conducted a prospective study of 8,361 male former students who underwent medical examinations while attending Glasgow University, Scotland, from 1948 to 1968. The mean age at examination was 20.5 (range, 16.1-30.0) years. The median follow-up time was 41.3 years. There were 863 deaths. In Cox proportional hazards modeling, there was no association between height and all-cause mortality with age-adjusted hazard ratios per 10-cm increase in height (hazard ratio = 0.92, 95% confidence interval: 0.83, 1.02). Height was inversely associated with all cardiovascular disease and coronary heart disease mortality, with hazard ratios per 10-cm increase in height of 0.78 (95% confidence interval: 0.66, 0.93) and 0.76 (95% confidence interval: 0.62, 0.93), respectively. Sizeable inverse associations with stroke and respiratory disease were also found, although these did not reach conventional levels of significance. There was no association with cancer or noncardiorespiratory disease mortality. There was a positive, although nonsignificant, association between height and mortality from aortic aneurysm. Controlling for confounding variables had little effect on these results. The findings suggest that factors operating in early life, and which influence height, also influence future cardiovascular health in men.

How quality of life data contribute to our understanding of cancer patients' experiences? A study of patients with lung cancer.

A prospective study was conducted to measure quality of life in newly diagnosed lung cancer patients attending a chest clinic in a large teaching and district general hospital in a geographically defined area (northern sector of Glasgow, Scotland). Quality of life was assessed at two points in time, pre-diagnosis (baseline) and 3 months after diagnosis (follow-up) using three standard measures; the Nottingham Health Profile (NHP); the European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ-C30), and its lung cancer supplement (QLQ-LC13). Out of 133 lung cancer patients diagnosed during the study period, 129 patients (97%) were interviewed pre-diagnosis. Of these, only 63% of the patients had an active treatment. Ninety-six patients were alive at follow-up, of whom 82 patients were re-interviewed. Thus, only 82 patients who had complete data were used in the analysis. Comparing patients' pre-diagnosis and follow-up scores on the NHP, only sleep difficulties improved slightly. Patients reported increased perceived health problems of all other characteristics studied (energy, p = 0.0004; physical mobility, p = 0.0008). Similar results were observed on the EORTC questionnaires indicating that patients' functioning and global quality of life had decreased. The only significant improvement after 3 months was seen in patients' cough (p = 0.006). There were marked increases in hair loss (p < 0.0001), constipation (p = 0.007), and sore mouth (p = 0.0004). The findings suggest that patient-centred variables should receive sufficient consideration in the treatment of lung cancer. The study results clearly indicate that information on quality of life contributes to our understanding of patients' experiences of their cancer treatment.

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.