July 11, Copyright: Assessing the potential for verification bias Because we only enrolled patients undergoing head imaging, it is possible that important injuries may have gone unrecognized among the unimaged patients. We previously developed a decision rule that appears to reliably identify patients with brain injuries, decreasing the need for CT scanning. These criteria were identified in our prior derivation study as indicators for potential candidates for our NEXUS head imaging DIs [ 8 ]. We assigned each patient to the following 3 final outcome classes: Because patients assigned low-risk classification are more prevalent than those requiring neurosurgical intervention, our final sample estimate was driven by the need to enroll patients who required neurosurgical intervention. Clinical use of our decision guide will allow physicians to reliably identify patients with serious brain injuries, while simultaneously decreasing the number of patients who require CT scanning. This approach maximized safety, ensuring that low-risk assignments were based on actual measured assessments rather than missing information.
An emergency physician at each center served as a study liaison and was charged with training participating clinicians in the criteria definitions and conduction of the study. Age 65 years or more is determined by available history. Results Between April 18, and December 10, , physicians ordered CT head imaging on 12, patients. Our primary outcome was the point measure and confidence interval CI for the sensitivity in detecting injuries that require neurosurgical intervention. Data collection At the time of enrollment, the treating clinician collected and recorded limited demographic information date of birth, sex, race, and ethnicity and documented whether DI criteria were present, absent, or could not be assessed for example coagulopathy in a comatose patient. Box 1 presents the detailed description of each criterion we provided to the treating clinicians. We also excluded patients who were transferred into a participating center with known intracranial injuries. Fig 1 presents the flow chart detailing patient enrollment, while Table 1 presents the characteristics of the enrolled patients. Author summary Why was this study done? To maximize compliance, participating centers adopted a protocol whereby CT imaging would not be performed until decision criteria had been assessed and recorded [ 19 ]. The DI assigned high-risk status to of patients with significant intracranial injuries sensitivity, Formal radiographic interpretations and outcome assignments were all completed without knowledge of the criteria assessments recorded for each patient. Outcome measures We defined our primary outcome a priori as the need for neurosurgical intervention, defined specifically as 1 death due to head injury, 2 need for craniotomy, 3 elevation of skull fracture, 4 intubation related to head injury, or 5 intracranial pressure monitoring, within 7 days of head injury [ 14 ]. The evaluation of blunt head injury patients can be challenging. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. In implementing the DI, we considered criteria that could not be assessed to be abnormal and excluded the patient from low-risk classification. We controlled all aspects of the study design, implementation, analysis, and manuscript preparation without influence from the grant funding agencies. Verifying sensitivity and NPV value at absolute levels is statistically and pragmatically impossible, but it is possible to estimate the lower confidence levels for these proportions to a Assessing the potential for verification bias Because we only enrolled patients undergoing head imaging, it is possible that important injuries may have gone unrecognized among the unimaged patients. In our study, the Canadian medium-risk rule exhibited a specificity of These criteria were identified in our prior derivation study as indicators for potential candidates for our NEXUS head imaging DIs [ 8 ]. The current assessment was specifically designed to validate this instrument in a new cohort, with sufficient precision in the measurement of the lower confidence limit for sensitivity, to ensure reliability [ 15 ]. Because most patients receive little or no benefit from imaging, while bearing the expense and radiation exposure, there has been a national push towards more selective use of head CTs in adult blunt head injury patients who are thought to be at low risk for significant injury [ 9 , 10 ]. Liaisons ensured that criterion assessments, radiographic results, and final outcomes were collected on all enrollees. Similar validation of the NPV requires assessments on patients assigned low-risk classification [ 21 ]. Neurologic deficit refers to any abnormal neurologic finding revealed by detailed testing. Medium-risk criteria [for significant brain injury]:
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