Mechanism matters: mortality and endothelial cell damage marker differences between blunt and penetrating traumatic injuries across three prehospital clinical trials.

Injury mechanism is an important consideration when conducting clinical trials in trauma. Mechanisms of injury may be associated with differences in mortality risk and immune response to injury, impacting the potential success of the trial. We sought to characterize clinical and endothelial cell damage marker differences across blunt and penetrating injured patients enrolled in three large, prehospital randomized trials which focused on hemorrhagic shock. In this secondary analysis, patients with systolic blood pressure < 70 or systolic blood pressure < 90 and heart rate > 108 were included. In addition, patients with both blunt and penetrating injuries were excluded. The primary outcome was 30-day mortality. Mortality was characterized using Kaplan-Meier and Cox proportional-hazards models. Generalized linear models were used to compare biomarkers. Chi squared tests and Wilcoxon rank-sum were used to compare secondary outcomes. We characterized data of 696 enrolled patients that met all secondary analysis inclusion criteria. Blunt injured patients had significantly greater 24-h (18.6% vs. 10.7%, log rank p = 0.048) and 30-day mortality rates (29.7% vs. 14.0%, log rank p = 0.001) relative to penetrating injured patients with a different time course. After adjusting for confounders, blunt mechanism of injury was independently predictive of mortality at 30-days (HR 1.84, 95% CI 1.06-3.20, p = 0.029), but not 24-h (HR 1.65, 95% CI 0.86-3.18, p = 0.133). Elevated admission levels of endothelial cell damage markers, VEGF, syndecan-1, TM, S100A10, suPAR and HcDNA were associated with blunt mechanism of injury. Although there was no difference in multiple organ failure (MOF) rates across injury mechanism (48.4% vs. 42.98%, p = 0.275), blunt injured patients had higher Denver MOF score (p < 0.01). The significant increase in 30-day mortality and endothelial cell damage markers in blunt injury relative to penetrating injured patients highlights the importance of considering mechanism of injury within the inclusion and exclusion criteria of future clinical trials.

Missingness matters: a secondary analysis of thromboelastography measurements from a recent prehospital randomized tranexamic acid clinical trial.

Background: Tranexamic acid (TXA) has been hypothesized to mitigate coagulopathy in patients after traumatic injury. Despite previous prehospital clinical trials demonstrating a TXA survival benefit, none have demonstrated correlated changes in thromboelastography (TEG) parameters. We sought to analyze if missing TEG data contributed to this paucity of findings. Methods: We performed a secondary analysis of the Study of Tranexamic Acid During Air Medical and Ground Prehospital Transport Trial. We compared patients that received TEG (YES-TEG) and patients unable to be sampled (NO-TEG) to analyze subgroups in which to investigate TEG differences. TEG parameter differences across TXA intervention arms were assessed within subgroups disproportionately present in the NO-TEG relative to the YES-TEG cohort. Generalized linear models controlling for potential confounders were applied to findings with p<0.10 on univariate analysis. Results: NO-TEG patients had lower prehospital systolic blood pressure (SBP) (100 (78, 140) vs 125 (88, 147), p<0.01), lower prehospital Glascow Coma Score (14 (3, 15) vs 15 (12, 15), p<0.01), greater rates of prehospital intubation (39.4% vs 24.4%, p<0.01) and greater mortality at 30 days (36.4% vs 6.8%, p<0.01). NO-TEG patients had a greater international normalized ratio relative to the YES-TEG subgroup (1.2 (1.1, 1.5) vs 1.1 (1.0, 1.2), p=0.04). Within a severe prehospital shock cohort (SBP<70), TXA was associated with a significant decrease in clot lysis at 30 min on multivariate analysis (ß=-27.6, 95% CI (-51.3 to -3.9), p=0.02). Conclusions: Missing data, due to the logistical challenges of sampling certain severely injured patients, may be associated with a lack of TEG parameter changes on TXA administration in the primary analysis. Previous demonstration of TXA's survival benefit in patients with severe prehospital shock in tandem with the current findings supports the notion that TXA acts at least partially by improving clot integrity. Level of evidence: Level II.