Traumatic accidents have long been classified in terms of their severity. The world’s oldest known surgical document, the Edwin Smith Surgical Papyrus (ca. 17th century bc), classified 48 traumatic injuries from ancient Egyptian battlefields and construction sites as successfully treatable, possibly curable, or untreatable.1 Such predictions about patient outcomes, and attempts to quantify the severity of traumatic accidents, are today the realm of injury severity scores (ISSs).
Trauma injury severity scoring quantifies the risk of an outcome following trauma. Injury scoring provides a single metric based on elements of clinical acumen and statistical theory to describe aspects of the patient condition after a traumatic incident. The primary outcome of interest is usually survival, though the outcome can be whatever one wants to measure: hospital or ICU length of stay (LOS), a vital sign such as blood pressure, performance of a procedure, or any other endpoint of interest.
Clinically, these “scores” assist in the prehospital triage of trauma patients and can help to more accurately predict patient outcomes to assist with clinical decision making, especially at the end of life. In the outcomes research setting, ISSs allow valid comparisons between disparate groups, which in turn can be translated into myriad applications: quality improvements in patient care, advancements in trauma systems and health care delivery, enhancements in injury prevention, valid benchmarking and quality control “report cards,” and epidemiological studies of trauma, among others.
Outcomes research is defined as a method of creating “empirically verified information” to better understand how variables in the real-world setting (from injury to treatment) affect a wide range of outcome variables (from mortality to satisfaction with care).2 Because outcomes are the product of many influences, the outcomes researcher must isolate the effects he or she wants to study from the effects of other “noisy” factors that can influence the outcome. This is called risk adjustment, or “case mix” adjustment, and is essential for proper outcomes analysis.
In trauma outcomes research, trauma ISSs are the essential tools for stratified risk adjustment, thereby allowing accurate comparisons among disparate patient populations with varied degrees of risk. The goal is to compare populations with similar degrees of traumatic injury so that other risk factors (time to treatment, mechanism, injury prevention equipment, etc.) may be properly isolated to examine their relationship to particular outcomes. Risk adjustment might be as simple as defining classes of a variable to stratify risk groups or as complicated as using a risk adjustor in a multivariable regression model.3
This chapter provides a background into injury severity scoring and outcomes research, reviewed in three sections. The first section, Injury Coding, discusses the two major schemes used to classify traumatic injury in the United States, the Abbreviated Injury Scale (AIS) and the International Classification of Diseases (ICD). The second section, Injury Severity Scoring, highlights the major trauma scoring systems used for outcome prediction and risk adjustment. The final ...