Fluoroscopic image-based behavior analysis can objectively explain subjective expert assessment of wire navigation skill.

Psychomotor skill and decision-making efficiency in surgical wire navigation can be objectively evaluated by analysis of intraoperative fluoroscopic image sequences. Prior work suggests that such image-based behavior analysis of operating room (OR) performance can predict performer experience level (R2 = 0.62) and agree with expert opinion (the current standard) on the quality of a final implant construct (R2 = 0.59). However, it is unclear how objective image-based evaluation compares with expert assessments for entire technical OR performances. This study examines the relationships between three key variables: (1) objective image-based criteria, (2) expert opinions, and (3) performing surgeon experience level. A paired-comparison survey of seven experts, based upon eight OR fluoroscopic wire navigation image sequences, shows that the experts' preferences are best explained by objective metrics that reflect psychomotor and decision-making behaviors which are counter-productive to successful implant placement, like image count (R2 = 0.83) and behavior tally (R2 = 0.74). One such behavior, adjustments away from goal, uniquely correlated well with all three key variables: a fluoroscopic image-based analysis composite score (R2 = 0.40), expert consensus (R2 = 0.76), and performer experience (R2 = 0.41). These results confirm that experts view less efficient technical behavior as indicative of lesser technical proficiency. While expert assessments of technical skill were reliable and consistent, neither individual nor consensus expert opinion appears to correlate with performer experience (R2 = 0.11).

A Dedicated Simulator Training Curriculum Improves Resident Performance in Surgical Management of Pediatric Supracondylar Humerus Fractures.

Background: The primary goal of including simulation in residency training is to improve technical skills while working outside of the operating room. Such simulation-related skill improvements have seldom been measured in the operating room. This is largely because uncontrolled variables, such as injury severity, patient comorbidity, and anatomical variation, can bias evaluation of an operating surgeon's skill. In this study, performance during the wire navigation phase of pediatric supracondylar humerus fracture fixation was quantitatively compared between 2 groups of orthopaedic residents: a standard training group consisting of residents who participated in a single simulator session of wire navigation training and an expanded training group consisting of residents who participated in a dedicated multifaceted wire navigation simulation training curriculum. Methods: To evaluate performance in the operating room, the full sequence of fluoroscopic images collected during wire navigation was quantitatively analyzed. Objective performance metrics included number of fluoroscopic images acquired, duration from placement of the first wire to that of the final wire, and wire spread at the level of the fracture. These metrics were measured from 97 pediatric supracondylar humerus fracture pinning surgeries performed by 28 different orthopaedic residents. Results: No differences were observed between the groups for wire spread in the final fluoroscopic images (t(94) = 0.75, p = 0.45), an important clinical objective of the surgery. Residents who received the expanded simulator training used significantly fewer fluoroscopic images (mean of 46 vs. 61 images, t(85) = 2.25, p < 0.03) and required less time from first to final wire placement (mean of 11.2 vs. 14.9 minutes, t(83) = 2.53, p = 0.013) than the standard training group. A post hoc review of Accreditation Council for Graduate Medical Education case logs for 24 cases from the standard training group and for 21 cases from the expanded training group indicated that, at the time of surgeries, residents who received expanded training had completed fewer comparable cases than residents in the standard training group (mean of 13 vs. 21, t(42) = 2.40 p = 0.02). Further regression analysis indicated that the expanded simulator training produced an effect comparable with that associated with completing 10.5 similar surgical case experiences. Conclusions: This study demonstrates that training on a wire navigation simulator can lead to improved performance in the operating room on a critical skill for all orthopaedic residents. By taking fewer images and less time while maintaining sufficient pin spread, simulator-trained residents were objectively measured to have improved performance in comparison with residents who had not participated in the pediatric elbow simulator curriculum. Clinical Relevance: As programs aim to provide safe and effective training for critical orthopaedic skills such as pinning a pediatric elbow, this study demonstrates a simulator curriculum that has demonstrated the transfer of skill from a learning environment to the operating room.

Establishing Construct Validity of a Novel Simulator for Guide Wire Navigation in Antegrade Femoral Intramedullary Nailing.

Background: Antegrade femoral intramedullary nailing (IMN) is a common orthopedic procedure that residents are exposed to early in their training. A key component to this procedure is placing the initial guide wire with fluoroscopic guidance. A simulator was developed to train residents on this key skill, building off an existing simulation platform originally developed for wire navigation during a compression hip screw placement. The objective of this study was to assess the construct validity of the IMN simulator. Methods: Thirty orthopedic surgeons participated in the study: 12 had participated in fewer than 10 hip fracture or IMN related procedures and were categorized as novices; 18 were faculty, categorized as experts. Both cohorts were instructed on the goal of the task, placing a guide wire for an IM nail, and the ideal wire position reference that their wire placement would be graded against. Participants completed 2 assessments with the simulator. Performance was graded on the distance from the ideal starting point, distance from the ideal end point, wire trajectory, duration, fluoroscopy image count, and other elements of surgical decision making. A two-way ANOVA analysis was used to analyze the data looking at experience level and trial number. Results: The expert cohort performed significantly better than the novice cohort on all metrics but one (overuse of fluoroscopy). The expert cohort had a more accurate starting point and completed the task while using fewer images and less overall time. Conclusion: This initial study shows that the IMN application of a wire navigation simulator demonstrates good construct validity. With such a large cohort of expert participants, we can be confident that this study captures the performance of active surgeons today. Implementing a training curriculum on this simulator has the potential to increase the performance of the novice level residents prior to their operating on a vulnerable patient. Level of Evidence: III.

Design and testing of a personalized noise monitoring system.

Agricultural workers are more prone to noise-induced hearing loss than are many other workers. Hearing protection device use among agricultural workers is low, but training can increase hearing protection device use. This work proposes a system designed to automatically inform agricultural workers when they were exposed to noises that exceed the National Institute for Occupational Safety and Health (NIOSH) recommended exposure level. The smartphone-based system worn on the arm uses a noise dosimeter to measure noise exposures throughout the day to within ±2 A-weighted decibels of a Class 2 sound level meter. The device collects location and audio data, which are transferred to a server and presented to the worker on a locally hosted website. The website details noise exposure and helps the worker identify where exposure occurred and what specific tasks exceed NIOSH's recommended exposure limit, putting them at higher risk of noise-induced hearing loss. With this understanding, the worker is expected to adopt behavior changes and better hearing protection use at critical places and times. This pilot study evaluates the accuracy of the noise dosimeter and GPS relative to gold-standard instruments. The system was tested on a farm with outputs compared with gold-standard instruments. A-weighted, 1-sec averaged sound pressure levels and position data were collected while users were performing a variety of tasks indoors and outdoors. The smartphone's external noise dosimeter read within ±2 A-weighted decibels of the Class 2 reference dosimeter 59% of the time. The positioning devices had an average error of sub-4 m. While not perfectly matching gold-standard instruments, the device is capable of identifying and collecting information relative to loud noise events that promote noise-induced hearing loss.

Minimally Trained Analysts Can Perform Fast, Objective Assessment of Orthopedic Technical Skill from Fluoroscopic Images.

Skill assessment in orthopedics has traditionally relied on subjective impressions from a supervising surgeon. The feedback derived from these tools may be limited by bias and other practical issues. Objective analysis of intraoperative fluoroscopic images offers an inexpensive, repeatable, and precise assessment strategy without bias. Assessors generally refrain from using the scores of images obtained throughout the operation to evaluate skill for practical reasons. A new system was designed to facilitate rapid analysis of this fluoroscopy via minimally trained analysts. Four expert and four novice analysts independently measured one objective metric for skill using both a custom analysis software and a commercial alternative. Analysts were able to measure the objective metric three times faster when using the custom software, and without a practical difference in accuracy in comparison to the expert analysts using the commercial software. These results suggest that a well-designed fluoroscopy analysis system can facilitate inexpensive, reliable, and objective assessment of surgical skills.

Combining physics-based and Kriging models to improve the estimation of noise exposure.

Worker exposure to occupational hazards is traditionally measured by equipping workers with wearable exposure monitors. An emerging alternative measurement first generates time-varying hazard maps from permanent monitors within the facility, then estimating worker exposure by integrating hazard levels traversed in map, following the tracked movement of workers. Complex environments may require many monitors to produce a hazard map with the necessary accuracy, but effective interpolation functions can reduce the required number of monitors needed. This work assesses the effectiveness of three models for accurately interpolating hazard levels among monitors: a traditional Kriging model, a physics-based model, and a hybrid model that combines the Kriging and physics-based models. The effectiveness of each interpolation function was tested with sound levels collected in four environmental settings. These detailed experimental data were used to generate over 10,000 simulation trials, where each trial configured the experimental data into a unique arrangement of simulated monitoring and sampling positions. For each simulation trial, the effectiveness of the three models was assessed with the root mean square error of the sound levels at the simulated sampling positions, using the simulated monitoring positions as input. The interpolated values between the monitored positions were analyzed separately from the extrapolated values beyond the monitored positions. The hybrid model consistently reported among the lowest errors in each trial. The Kriging model performed best for the densest networks (those with the most monitors). Even in these cases, the hybrid model performed within 10% of the Kriging model with less than a third of the monitors. The experiment demonstrates that the hybrid model is highly effective at estimating hazardous sound levels; future work may demonstrate similar advantages for gas and aerosol hazards.

Failure of Orthopaedic Residents to Voluntarily Participate in a Laboratory Skills Training.

INTRODUCTION: Arthroscopy simulation is increasingly used in orthopaedic residency training. The implementation of a curriculum to accommodate these new training tools is a point of interest. We assessed the use of a high-fidelity arthroscopy simulator in a strictly voluntary curriculum to gauge resident interest and educational return. METHODS: Fifty-eight months of simulator use data were collected from a single institution to analyze trends in resident use. Comparable data from two additional residency programs were analyzed as well, for comparison. Orthopaedic residents were surveyed to gauge interest in continued simulation training. RESULTS: Average annual simulator use at the study institution was 27.7 hours (standard deviation = 26.8 hours). Orthopaedic residents spent an average of 1.7 hours practicing on the simulation trainer during the observation period. A total of 21% of residents met or exceeded a minimum of 3 hours of simulation time required for skill improvement defined by literature. Most (86%) of the residents agreed that the simulator in use should become a mandated component of a junior resident training. CONCLUSION: Although surgical simulation has a role in orthopaedic training, voluntary simulator use is sporadic, resulting in many residents not receiving the full educational benefits of such training. Implementation of a mandated simulation training curriculum is desired by residents and could improve the educational return of surgical simulators in residency training.

Surgical Skill Can be Objectively Measured From Fluoroscopic Images Using a Novel Image-based Decision Error Analysis (IDEA) Score.

BACKGROUND: To advance orthopaedic surgical skills training and assessment, more rigorous and objective performance measures are needed. In hip fracture repair, the tip-apex distance is a commonly used summative performance metric with clear clinical relevance, but it does not capture the skill exercised during the process of achieving the final implant position. This study introduces and evaluates a novel Image-based Decision Error Analysis (IDEA) score that better captures performance during fluoroscopically-assisted wire navigation. QUESTIONS/PURPOSES: (1) Can wire navigation skill be objectively measured from a sequence of fluoroscopic images? (2) Are skill behaviors observed in a simulated environment also exhibited in the operating room? Additionally, we sought to define an objective skill metric that demonstrates improvement associated with accumulated surgical experience. METHODS: Performance was evaluated both on a hip fracture wire navigation simulator and in the operating room during actual fracture surgery. After examining fluoroscopic image sequences from 176 consecutive simulator trials (performed by 58 first-year orthopaedic residents) and 21 consecutive surgical procedures (performed by 19 different orthopaedic residents and one attending orthopaedic surgeon), three main categories of erroneous skill behavior were identified: off-target wire adjustments, out-of-plane wire adjustments, and off-target drilling. Skill behaviors were measured by comparing wire adjustments made between consecutive images against the goal of targeting the apex of the femoral head as part of our new IDEA scoring methodology. Decision error metrics (frequency, magnitude) were correlated with other measures (image count and tip-apex distance) to characterize factors related to surgical performance on both the simulator and in the operating room. An IDEA composite score integrating decision errors (off-target wire adjustments, out-of-plane wire adjustments, and off-target drilling) and the final tip-apex distance to produce a single metric of overall performance was created and compared with the number of hip wire navigation cases previously completed (such as surgeon experience levels). RESULTS: The IDEA methodology objectively analyzed 37,000 images from the simulator and 688 images from the operating room. The number of decision errors (7 ± 5 in the operating room and 4 ± 3 on the simulator) correlated with fluoroscopic image count (33 ± 14 in the operating room and 20 ± 11 on the simulator) in both the simulator and operating room environments (R2 = 0.76; p < 0.001 and R2 = 0.71; p < 0.001, respectively). Decision error counts did not correlate with the tip-apex distance (16 ± 4 mm in the operating room and 12 ± 5 mm on the simulator) for either the simulator or the operating room (R2 = 0.08; p = 0.15 and R2 = 0.03; p = 0.47, respectively), indicating that the tip-apex distance is independent of decision errors. The IDEA composite score correlated with surgical experience (R2 = 0.66; p < 0.001). CONCLUSION: The fluoroscopic images obtained in the course of placing a guide wire contain a rich amount of information related to surgical skill. This points the way to an objective measure of skill that also has potential as an educational tool for residents. Future studies should expand this analysis to the wide variety of procedures that rely on fluoroscopic images. CLINICAL RELEVANCE: This study has shown how resident skill development can be objectively assessed from fluoroscopic image sequences. The IDEA scoring provides a basis for evaluating the competence of a resident. The score can be used to assess skill at key timepoints throughout residency, such as when rotating onto/off of a new surgical service and before performing certain procedures in the operating room, or as a tool for debriefing/providing feedback after a procedure is completed.

A Vision for Using Simulation & Virtual Coaching to Improve the Community Practice of Orthopedic Trauma Surgery.

Background: Many orthopedic surgeries involve the challenging integration of fluoroscopic image interpretation with skillful tool manipulation to enable procedures to be performed through less invasive approaches. Simulation has proved beneficial for teaching and improving these skills for residents, but similar benefits have not yet been realized for practicing orthopedic surgeons. A vision is presented to elevate community orthopedic practice and improve patient safety by advancing the use of simulators for training and assessing surgical skills. Methods: Key elements of this vision that are established include 1) methods for the objective and rigorous assessment of the performance of practicing surgeons now exist, 2) simulators are sufficiently mature and sophisticated that practicing surgeons will use them, and 3) practicing surgeons can improve their performance with appropriate feedback and coaching. Results: Data presented indicate that surgical performance can be adequately and comparably measured using structured observations made by experts or non-expert crowds, with the crowdsourcing approach being more expedient and less expensive. Rigorous measures of the surgical result and intermediate objectives obtained semi-automatically from intra-operative fluoroscopic image sequences can distinguish performances of experts from novices. Experience suggests that practicing orthopedic surgeons are open to and can be constructively engaged by a family of mature simulators as a means to evaluate and improve their surgical skills. Conclusions: The results presented support our contention that new objective assessment measures are sufficient for evaluating the performance of working surgeons. The novel class of orthopedic surgical simulators available were tested and approved by practicing physicians. There exists a clear opportunity to combine purpose-designed simulator exercises with virtual coaching to help practicing physicians retain, retrain, and improve their technical skills. This will ultimately reduce cost, increase the quality of care, and decrease complication rates. Clinical Relevance: This vision articulates a means to boost the confidence of practitioners and ease their anxiety so that they perform impactful procedures more often in community hospitals, which promises to improve treatment and reduce the cost of care while keeping patients closer to their homes and families.

Estimating personal exposures from a multi-hazard sensor network.

Occupational exposure assessment is almost exclusively accomplished with personal sampling. However, personal sampling can be burdensome and suffers from low sample sizes, resulting in inadequately characterized workplace exposures. Sensor networks offer the opportunity to measure occupational hazards with a high degree of spatiotemporal resolution. Here, we demonstrate an approach to estimate personal exposure to respirable particulate matter (PM), carbon monoxide (CO), ozone (O3), and noise using hazard data from a sensor network. We simulated stationary and mobile employees that work at the study site, a heavy-vehicle manufacturing facility. Network-derived exposure estimates compared favorably to measurements taken with a suite of personal direct-reading instruments (DRIs) deployed to mimic personal sampling but varied by hazard and type of employee. The root mean square error (RMSE) between network-derived exposure estimates and personal DRI measurements for mobile employees was 0.15 mg/m3, 1 ppm, 82 ppb, and 3 dBA for PM, CO, O3, and noise, respectively. Pearson correlation between network-derived exposure estimates and DRI measurements ranged from 0.39 (noise for mobile employees) to 0.75 (noise for stationary employees). Despite the error observed estimating personal exposure to occupational hazards it holds promise as an additional tool to be used with traditional personal sampling due to the ability to frequently and easily collect exposure information on many employees.

Advancing Simulation-Based Orthopaedic Surgical Skills Training: An Analysis of the Challenges to Implementation.

Simulation-based surgical skills training is recognized as a valuable method to improve trainees' performance and broadly perceived as essential for the establishment of a comprehensive curriculum in surgical education. However, there needs to be improvement in several areas for meaningful integration of simulation into surgical education. The purpose of this focused review is to summarize the obstacles to a comprehensive integration of simulation-based surgical skills training into surgical education and board certification and suggest potential solutions for those obstacles. First and foremost, validated simulators need to be rigorously assessed to ensure their feasibility and cost-effectiveness. All simulation-based courses should include clear objectives and outcome measures (with metrics) for the skills to be practiced by trainees. Furthermore, these courses should address a wide range of issues, including assessment of trainees' problem-solving and decision-making abilities and remediation of poor performance. Finally, which simulation-based surgical skills courses will become a standard part of the curriculum across training programs and which will be of value in board certification should be precisely defined. Sufficient progress in these areas will prevent excessive development of training and assessment tools with duplicative effort and large variability in quality.

An Extensible Orthopaedic Wire Navigation Simulation Platform.

The demand for simulation-based skills training in orthopaedics is steadily growing. Wire navigation, or the ability to use 2D images to place an implant through a specified path in bone, is an area of training that has been difficult to simulate given its reliance on radiation based fluoroscopy. Our group previously presented on the development of a wire navigation simulator for a hip fracture module. In this paper, we present a new methodology for extending the simulator to other surgical applications of wire navigation. As an example, this paper focuses on the development of an iliosacral wire navigation simulator. We define three criteria that must be met to adapt the underlying technology to new areas of wire navigation; surgical working volume, system precision, and tactile feedback. The hypothesis being that techniques which fall within the surgical working volume of the simulator, demand a precision less than or equal to what the simulator can provide, and that require the tactile feedback offered through simulated bone can be adopted into the wire navigation module and accepted as a valid simulator for the surgeons using it. Using these design parameters, the simulator was successfully configured to simulate the task of drilling a wire for an iliosacral screw. Residents at the University of Iowa successfully used this new module with minimal technical errors during use.

Sources of error and variability in particulate matter sensor network measurements.

The quality of mass concentration estimates from increasingly popular networks of low-cost particulate matter sensors depends on accurate conversion of sensor output (e.g., voltage) into gravimetric-equivalent mass concentration, typically using a calibration procedure. This study evaluates two important sources of variability that lead to error in estimating gravimetric-equivalent mass concentration: the temporal changes in sensor calibration and the spatial and temporal variability in gravimetric correction factors. A 40-node sensor network was deployed in a heavy vehicle manufacturing facility for 8 months. At a central location in the facility, particulate matter was continuously measured with three sensors of the network and a traditional, higher-cost photometer, determining the calibration slope and intercept needed to translate sensor output to photometric-equivalent mass concentration. Throughout the facility, during three intensive sampling campaigns, respirable mass concentrations were measured with gravimetric samplers and photometers to determine correction factors needed to adjust photometric-equivalent to gravimetric-equivalent mass concentration. Both field-determined sensor calibration slopes and intercepts were statistically different than those estimated in the laboratory (α = 0.05), emphasizing the importance of aerosol properties when converting voltage to photometric-equivalent mass concentration and the need for field calibration to determine slope. Evidence suggested the sensors' weekly field calibration slope decreased and intercept increased, indicating the sensors were deteriorating over time. The mean correction factor in the cutting and shot blasting area (2.9) was substantially and statistically lower than that in the machining and welding area (4.6; p = 0.01). Therefore, different correction factors should be determined near different occupational processes to accurately estimate particle mass concentrations.

Do Skills Acquired from Training with a Wire Navigation Simulator Transfer to a Mock Operating Room Environment?

BACKGROUND: Skills training and simulation play an increasingly important role in orthopaedic surgical education. The intent of simulation is to improve performance in the operating room (OR), a trait known as transfer validity. No prior studies have explored how simulator-based wire navigation training can transfer to higher-level tasks. Additionally, there is a lack of knowledge on the format in which wire navigation training should be deployed. QUESTIONS/PURPOSES: (1) Which training methods (didactic content, deliberate practice, or proficiency-based practice) lead to the greatest improvement in performing a wire navigation task? (2) Does a resident's performance using a wire navigation simulator correlate with his or her performance on a higher-level simulation task in a mock OR involving a C-arm, a radiopaque femur model, and a large soft tissue surrogate surrounding the femur? METHODS: Fifty-five residents from four different medical centers participated in this study over the course of 2 years. The residents were divided into three groups: traditional training (included first-year residents from the University of Iowa, University of Minnesota, and the Mayo Clinic), deliberate practice (included first-year residents from the University of Nebraska and the University of Minnesota), and proficiency training (included first-year residents from the University of Minnesota and the Mayo Clinic). Residents in each group received a didactic introduction covering the task of placing a wire to treat an intertrochanteric fracture, and this was considered traditional training. Deliberate practice involved training on a radiation-free simulator that provided specific feedback throughout the practice sessions. Proficiency training used the same simulator to train on specific components of wire navigation, like finding the correct starting point, to proficiency before moving to assessment. The wire navigation simulator uses a camera system to track the wire and provide computer-generated fluoroscopy. After training, task performance was assessed in a mock OR. Residents from each group were assessed in the mock OR based on their use of fluoroscopy, total time, and tip-apex distance. Correlation analysis was performed to examine the relationship between resident performance on the simulator and in the mock OR. RESULTS: Residents in the two simulation-based training groups had a lower tip-apex distance than those in the traditional training group (didactic training tip-apex distance: 24 ± 7 mm, 95% CI, 20-27; deliberate practice tip-apex distance: 16 ± 5 mm, 95% CI, 13-19, p = 0.001; proficiency training tip-apex distance: 15 ± 4 mm, 95% CI, 13-18, p < 0.001). Residents in the proficiency training group used more images than those in the other groups (didactic training: 22 ± 12 images, p = 0.041; deliberate practice: 19 ± 8 images; p = 0.012, proficiency training: 31 ± 14 images). In the two simulation-based training groups, resident performance on the simulator, that is, tip-apex distance, image use, and overall time, was correlated with performance in the mock OR (r-square = 0.15 [p = 0.030], 0.61 [p < 0.001], and 0.43 [p < 0.001], respectively). CONCLUSIONS: As residency programs are designing their curriculum to train wire navigation skills, emphasis should be placed on providing an environment that allows for deliberate practice with immediate feedback about their performance. Simulators such as the one presented in this study offer a safe environment for residents to learn this key skill. LEVEL OF EVIDENCE: Level II, therapeutic study.

Mapping Occupational Hazards with a Multi-sensor Network in a Heavy-Vehicle Manufacturing Facility.

Due to their small size, low-power demands, and customizability, low-cost sensors can be deployed in collections that are spatially distributed in the environment, known as sensor networks. The literature contains examples of such networks in the ambient environment; this article describes the development and deployment of a 40-node multi-hazard network, constructed with low-cost sensors for particulate matter (SHARP GP2Y1010AU0F), carbon monoxide (Alphasense CO-B4), oxidizing gases (Alphasense OX-B421), and noise (developed in-house) in a heavy-vehicle manufacturing facility. Network nodes communicated wirelessly with a central database in order to record hazard measurements at 5-min intervals. Here, we report on the temporal and spatial measurements from the network, precision of network measurements, and accuracy of network measurements with respect to field reference instruments through 8 months of continuous deployment. During typical production periods, 1-h mean hazard levels ± standard deviation across all monitors for particulate matter (PM), carbon monoxide (CO), oxidizing gases (OX), and noise were 0.62 ± 0.2 mg m-3, 7 ± 2 ppm, 155 ± 58 ppb, and 82 ± 1 dBA, respectively. We observed clear diurnal and weekly temporal patterns for all hazards and daily, hazard-specific spatial patterns attributable to general manufacturing processes in the facility. Processes associated with the highest hazard levels were machining and welding (PM and noise), staging (CO), and manual and robotic welding (OX). Network sensors exhibited varying degrees of precision with 95% of measurements among three collocated nodes within 0.21 mg m-3 for PM, 0.4 ppm for CO, 9 ppb for OX, and 1 dBA for noise of each other. The median percent bias with reference to direct-reading instruments was 27%, 11%, 45%, and 1%, for PM, CO, OX, and noise, respectively. This study demonstrates the successful long-term deployment of a multi-hazard sensor network in an industrial manufacturing setting and illustrates the high temporal and spatial resolution of hazard data that sensor and monitor networks are capable of. We show that network-derived hazard measurements offer rich datasets to comprehensively assess occupational hazards. Our network sets the stage for the characterization of occupational exposures on the individual level with wireless sensor networks.

Efficacy of Paired Electrochemical Sensors for Measuring Ozone Concentrations.

Typical low-cost electrochemical sensors for ozone (O3) are also highly responsive to nitrogen dioxide (NO2). Consequently, a single sensor's response to O3 is indistinguishable from its response to NO2. Recently, a method for quantifying O3 concentrations became commercially available (Alphasense Ltd., Essex, UK): collocating a pair of sensors, a typical oxidative gas sensor that responds to both O3 and NO2 (model OX-B431) and a second similar sensor that filters O3 and responds only to NO2 (model NO2-B43F). By pairing the two sensors, O3 concentrations can be calculated. We calibrated samples of three NO2-B43F sensors and three OX-B431 sensors with NO2 and O3 exclusively and conducted mixture experiments over a range of 0-1.0 ppm NO2 and 0-125 ppb O3 to evaluate the ability of the paired sensors to quantify NO2 and O3 concentrations in mixture. Although the slopes of the response among our samples of three sensors of each type varied by as much as 37%, the individual response of the NO2-B43F sensors to NO2 and OX-B431 sensors to NO2 and O3 were highly linear over the concentrations studied (R2 ≥ 0.99). The NO2-B43F sensors responded minimally to O3 gas with statistically non-significant slopes of response. In mixtures of NO2 and O3, quantification of NO2 was generally accurate with overestimates up to 29%, compared to O3, which was generally underestimated by as much as 187%. We observed changes in sensor baseline over 4 days of experiments equivalent to 34 ppb O3, prompting an alternate method of calculating concentrations by baseline-correcting sensor signal. The baseline-correction method resulted in underestimates of NO2 up to 44% and decreases in the underestimation of O3 up to 107% for O3. Both methods for calculating gas concentrations progressively underestimated O3 concentrations as the ratio of NO2 signal to O3 signal increased. Our results suggest that paired NO2-B43F and OX-B431 sensors permit quantification of NO2 and O3 in mixture, but that O3 concentration estimates are less accurate and precise than those for NO2.

Sensor Selection to Improve Estimates of Particulate Matter Concentration from a Low-Cost Network.

Deployment of low-cost sensors in the field is increasingly popular. However, each sensor requires on-site calibration to increase the accuracy of the measurements. We established a laboratory method, the Average Slope Method, to select sensors with similar response so that a single, on-site calibration for one sensor can be used for all other sensors. The laboratory method was performed with aerosolized salt. Based on linear regression, we calculated slopes for 100 particulate matter (PM) sensors, and 50% of the PM sensors fell within ±14% of the average slope. We then compared our Average Slope Method with an Individual Slope Method and concluded that our first method balanced convenience and precision for our application. Laboratory selection was tested in the field, where we deployed 40 PM sensors inside a heavy-manufacturing site at spatially optimal locations and performed a field calibration to calculate a slope for three PM sensors with a reference instrument at one location. The average slope was applied to all PM sensors for mass concentration calculations. The calculated percent differences in the field were similar to the laboratory results. Therefore, we established a method that reduces the time and cost associated with calibration of low-cost sensors in the field.

Developing an objective assessment of surgical performance from operating room video and surgical imagery.

An unbiased, repeatable process for assessing operating room performance is an important step toward quantifying the relationship between surgical training and performance. Hip fracture surgeries offer a promising first target in orthopedic trauma because they are common and they offer quantitative performance metrics that can be assessed from video recordings and intraoperative fluoroscopic images. Hip fracture repair surgeries were recorded using a head-mounted point-of-view camera. Intraoperative fluoroscopic images were also saved. The following performance metrics were analyzed: duration of wire navigation, number of fluoroscopic images collected, degree of intervention by the surgeon's supervisor, and the tip-apex distance (TAD). Two orthopedic traumatologists graded surgical performance in each video independently using an Objective Structured Assessment of Technical Skill (OSATS). Wire navigation duration correlated with weeks into residency and prior cases logged. TAD correlated with cases logged. There was no significant correlation between the OSATS total score and experience metrics. Total OSATS score correlated with duration and number of fluoroscopic images. Our results indicate that two metrics of hip fracture wire navigation performance, duration and TAD, significantly differentiate surgical experience. The methods presented have the potential to provide truly objective assessment of resident technical performance in the OR.

Low-Cost, Distributed Environmental Monitors for Factory Worker Health.

An integrated network of environmental monitors was developed to continuously measure several airborne hazards in a manufacturing facility. The monitors integrated low-cost sensors to measure particulate matter, carbon monoxide, ozone and nitrogen dioxide, noise, temperature and humidity. The monitors were developed and tested in situ for three months in several overlapping deployments, before a full cohort of 40 was deployed in a heavy vehicle manufacturing facility for a year of data collection. The monitors collect data from each sensor and report them to a central database every 5 min. The work includes an experimental validation of the particle, gas and noise monitors. The R² for the particle sensor ranges between 0.98 and 0.99 for particle mass densities up to 300 μg/m³. The R² for the carbon monoxide sensor is 0.99 for concentrations up to 15 ppm. The R² for the oxidizing gas sensor is 0.98 over the sensitive range from 20 to 180 ppb. The noise monitor is precise within 1% between 65 and 95 dBA. This work demonstrates the capability of distributed monitoring as a means to examine exposure variability in both space and time, building an important preliminary step towards a new approach for workplace hazard monitoring.