Abstract [from journal]
Background: Trauma centers with low observed:expected (O:E) mortality ratios are considered high performers; however, it is unknown whether improvements in this ratio are due to a small number of unexpected survivors with high mortality risk (big saves) or a larger number of unexpected survivors with moderate mortality risk (marginal gains). We hypothesized that the highest-performing centers achieve that status via larger numbers of unexpected survivors with moderate mortality risk.
Methods: We calculated O:E ratios for trauma centers in Pennsylvania for 2016 using a risk-adjusted mortality model. We identified high and low performers as centers whose 95% CIs did not cross 1. We visualized differences between these centers by plotting patient-level observed and expected mortality; we then examined differences in a subset of patients with a predicted mortality of ≥10% using the chi-squared test.
Results: One high performer and 1 low performer were identified. The high performer managed a population with more blunt injuries (97.2% vs 93.6%, P < .001) and a higher median Injury Severity Score (14 vs 11, P < .001). There was no difference in survival between these centers in patients with an expected mortality of <10% (98.0% vs 96.7%, P = .11) or ≥70% (23.5% vs 10.8%, P = .22), but there was a difference in the subset with an expected mortality of ≥10% (77.5% vs 43.1%, P < .001).
Conclusions: Though patients with very low predicted mortality do equally well in high-performing and low-performing centers, the fact that performance seems determined by outcomes of patients with moderate predicted mortality favors a "marginal gains" theory.