Abstract 230: Differential Effects of Prehospital Hypotension and Injury Severity in Isolated vs. Multisystem Major Traumatic Brain Injury

Abstract

Background: In hospital-based studies, hypotension (HT, SBP <90) is more likely to occur in multisystem traumatic brain injury (MTBI) than isolated (ITBI). However, there are few EMS studies on this issue. Hypothesis: Prehospital HT is associated with differential effects in MTBI and ITBI and these effects are influenced by the severity of primary brain injury. Methods: Inclusion: TBI cases in the EPIC Study (NIH 1R01NS071049) before TBI guideline implementation (1/07-3/14). ITBI: Major TBI cases (CDC Barell Matrix Type 1) that had no injury with ICD9-based Regional Severity Score [RSS (AIS equivalent)] ≥3 in any other body region. MTBI: Type 1 TBI plus at least one non-head region injury with RSS ≥3. Results: Included were 13,435 cases [Excl: age <10 (5.9%), missing data (6.2%)]. 10,374 (77.2%) were ITBI, 3061 (22.8%) MTBI. Mortality: ITBI: 7.7% (797/10,374), MTBI: 19.2% (587/3061, p<0.0001). Prehospital HT occurred 3.5 times more often in MTBI (14.8%, 453/3061 vs 4.2%, 437/10,374; p<0.0001). Among HT cases, 40.8% (185/453) with MTBI died vs 30.9% with ITBI (135/437; p<0.0001). In the hypotensive moderate/severe TBI cohort (RSS-Head 3/4), MTBI mortality was 2.4 times higher (17.2%, 40/232) than ITBI (7.1%, 17/240, p = 0.001). However, in the hypotensive very/extremely severe TBI group (RSS-Head 5/6), mortality was almost identical in MTBI (73.4%, 141/192) and ITBI (72.1%, 116/161, p = 0.864). Conclusion: Among major TBI patients with prehospital HT, those with MTBI were much more likely to die than those with ITBI. However, this association varied dramatically with TBI severity. In mod/severe TBI cases with HT, MTBI mortality was 2.4 times higher than in ITBI. In contrast, in very/extremely severe TBI with HT, there was no identifiable mortality difference. Thus, in cases with substantial potential to survive the primary brain injury (mod/severe), outcome is markedly worse in patients with multisystem injuries. However, in very/extremely severe TBI, non-head region injuries have no apparent association with mortality. This may be because the TBI is the primary factor leading to death in these cases. The main EPIC study is evaluating whether this severity-based difference in “effect” has implications for TBI guideline treatment effectiveness.