Chapter 5: Injury Severity Scoring and Outcomes Research

INTRODUCTION

Injuries have long been classified in terms of 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 injury, are today the realm of more than 50 published injury severity scores, scales, and models.

Injury severity scoring quantifies the risk of an outcome following trauma and provides metrics based on elements of clinical acumen and statistical modeling to describe aspects of the patient condition post-injury. The primary outcome of interest is commonly survival or a measure of morbidity (eg, complications) or resource use (eg, hospital or intensive care unit [ICU] length of stay [LOS]), but may be any primary endpoint of interest (eg, compliance to an evidence-based procedure).

The injury scores and models discussed here are generally applied using retrospectively collected data. They are therefore suitable for case mix adjustment or risk prediction in groups of patients but are not appropriate for individual patient predictions to guide clinical management decisions. They have a host of applications including quality improvements in patient care, trauma systems and health care delivery, injury prevention initiatives, and epidemiological studies of injury. Patient-specific clinical prediction applications are more simple, requiring decision rules to categorize patients into low-risk/high-risk “bins” and present less sophisticated statistical demand.

DEFINITIONS

This chapter provides a concise description of injury severity scoring and modeling, with particular emphasis on application to outcomes research and quality improvement. Because there can be confusion about the precise meaning of terminologies used in this process, a few definitions are warranted to distinguish the qualitative from the quantitative.

Scores: Injury severity scores place numerical values on injury descriptions, thus enabling standardized communication about the injury state. Scores should be as objective as possible and their assignment should be supported by inter- and intrarater reliability studies.

Scales: Scales are a ranking, based on consensus, assessment, or mathematics and statistics, of risk or severity. Examples include the Glasgow Coma Scale (GCS), which ranges from 3 (deep coma) to 15 (full consciousness) and the Abbreviated Injury Scale (AIS) score, which generally ranks severity from 1 (minor) to 6 (virtually unsurvivable, Table 5-1).

Scales can be

• Nominal: the values of the score are not numerical and have no order

• Ordinal: the values of the score are not numerical but have an order (eg, increasing or decreasing injury severity)

• Interval: the values of the ...