Sudden survival improvement in critical neurotrauma: An exploratory analysis using a stratified statistical process control technique

Abstract

Background: Outcome after trauma depends on patient characteristics, quality of care, and random events. The TRISS model predicts probability of survival (Ps) adjusted for Injury Severity Score (ISS), Revised Trauma Score (RTS), mechanism of injury, and age. Quality of care is often evaluated by calculating the number of "excess" survivors, year by year. In contrast, the Variable Life-Adjusted Display (VLAD) technique allows rapid detection of altered survival. VLAD adjusts each death or survival by the patient's risk status and graphically displays accumulated number of unexpected survivors over time. We evaluated outcome changes and their time relation to trauma service improvements.

Methods: Observational, retrospective study of the total 2001-2011 trauma population from a Level I trauma centre. Outcome was 30-day survival. Ps was calculated with the TRISS model, 2005 coefficients. VLAD graphs were created for the entire population and for subpopulations stratified by ISS level, ISS body region (Head/Neck, Face, Chest, Abdomen/Pelvic contents, Extremities/Pelvic girdle, External), and maximum Abbreviated Injury Scale (maxAIS) score in each region. Piecewise linear regression identified VLAD graph breakpoints.

Results: 12,191 consecutive trauma patients (median age 35 years, 72% males, 91% blunt injury, 41% ISS≥16) formed the dataset. Their VLAD graph indicated performance equal to TRISS predicted survival until a sudden improvement in late 2004. From then survival remained improved but unchanged through 2011. Total number of excess survivors was 141. Inspection of subgroup VLAD graphs showed that the increased survival mainly occurred in patients having at least one Head/Neck AIS 5 injury. The effect was present in both isolated and multitraumatised maxAIS 5 Head/Neck trauma. The remaining trauma population showed unchanged survival, superior to TRISS predicted, throughout the study period. Important general and neurotrauma-targeted improvements in our trauma service could underlie our findings: A formalised trauma service, damage control resuscitation protocols, structured training, increased helicopter transfer capacity, consultant-based neurosurgical assessment, a doubling of emergency neurosurgical procedures, and improved neurointensive care.

Conclusions: Stratified VLAD enables continuous, high-resolution system analysis. We encourage trauma centres to explore their data and to monitor future system changes.

Keywords: CUSUM technique; Outcome monitoring; Quality of care; Trauma system; Variable Life-Adjusted Display.