Journal Watch: The Best Blood Pressures for TBI

Reviewed This Month

• Optimal Out-of-Hospital Blood Pressure in Major Traumatic Brain Injury: A Challenge to the Current Understanding of Hypotension
• Authors: Spaite DW, Hu C, Bobrow BJ, et al.
• Published in: Annals of Emergency Medicine, March 2022

This month we review an interesting study that sought to identify systolic blood pressure (SBP) ranges associated with “optimal” outcomes in patients suffering major traumatic brain injury (TBI). The authors of this study described the tremendous societal burden of TBI, which results in more than 2 million emergency department visits, more than a quarter-million hospitalizations, and more than 50,000 deaths in the US annually. Further, the authors noted, more than 5 million Americans have long-term disabilities due to TBIs. 

Recently published evidence-based guidelines have been shown to improve the odds of survival among patients with TBI. These guidelines use an SBP of 90 mmHg as a threshold for treating hypotension but acknowledge “it is possible that SBP higher than 90 mmHg would be desirable during the out-of-hospital and resuscitation phase.” However, at the time the guidelines were published, no large-scale studies had been performed that evaluated SBP on a continuous scale. Rather, most used predefined thresholds for hypotension, normotension, and hypertension. 

The objective of this study was to analyze the association between out-of-hospital blood pressure and outcomes across the entire range of values. This was a preplanned secondary analysis from the Excellence in Prehospital Injury Care (EPIC) TBI study. EPIC was a statewide collaboration between Arizona fire departments, ground and air EMS transport agencies, the University of Arizona, and the Arizona Department of Health Services. The goal of EPIC was to “dramatically increase the number of severe TBI victims who survive with good neurologic outcome by thoroughly implementing the national EMS TBI guidelines.” The EPIC study database contained nearly 22,000 major TBI cases with linked out-of-hospital and hospital data. This database provided a unique opportunity to perform the analyses needed to meet the study objective. 

Parameters

To be included in this study, patients had to be enrolled in the EPIC study. Inclusion criteria for the EPIC study were that the patient suffered from physical trauma and was transported directly or transferred to a Level I trauma center by a participating EMS agency and had hospital-diagnosed TBI. Additionally, patients had to meet one of the following criteria: an Abbreviated Injury Scale head score of 3 or more, a Barell Matrix type 1 evaluation, and out-of-hospital positive-pressure ventilation by BVM, endotracheal intubation, supraglottic airway, nasal intubation, or cricothyrotomy. 

Additionally, both patients with isolated TBIs and TBIs with multisystem injury were included. Patients were excluded from this secondary analysis if they were less than 10 years or had an SBP of less than 40 mmHg. Interfacility transfers were also excluded. Finally, cases that were missing age, SBP, or trauma type (blunt vs. penetrating) were excluded. The authors explained that patients younger than 10 were excluded because the guideline-based threshold for defining hypotension changes with each year of age from 0–9 but remains constant for patients 10 or older. 

The analysis included regression models adjusted for age, sex, race, ethnicity, out-of-hospital hypoxia, out-of-hospital airway management, Injury Severity Score, head-region injury score matched to AIS score, trauma type (blunt vs. penetrating), payment source, multisystem injury, out-of-hospital CPR, and treating trauma center. 

Results

There were 21,852 patients included in the initial EPIC study. After exclusions there were 12,169 included in this analysis. There were 12% of patients who died. This high percentage of death was due to the focus of the EPIC study on major TBI. 

The study population was mostly male (70%). There were 78% that had their race documented as White, 4% Black, 5% American Indian/Alaska Native, 1% Asian, 1% unknown, and 11% other. There were 22% that had their ethnicity documented as Hispanic. Almost three-quarters (72%) were isolated TBI patients. About 2% had out-of-hospital CPR performed. Most (78%) had no airway management performed out-of-hospital, while 17% had an advanced airway placed, and 5% had positive pressure provided by BVM. 

With respect to secondary outcomes of interest, 10% of patients had out-of-hospital hypoxia. There were 2% who died before hospital admission. Among those who were admitted, 81% were admitted to the ICU. There were 56% discharged home. 

When describing the adjusted mortality plot of SBP and death, the authors identified 3 distinct attributes. First, they noted that the probability of death rapidly decreased with out-of-hospital SBPs from 40–130 mmHg. The curve then flattened at a low probability of death until about 180 mmHg, at which point there was a rapid increase in the probability of death. The SBP ≥180 group was also much more likely to have severe brain injury compared to patients with SBPs from 120–179 mmHg. These plots of secondary outcomes showed significant similarities in the slopes of the lines when compared to the mortality plot. Interestingly, the plots were almost identical when only evaluating blunt injuries as well as in a sensitivity analysis that only included patients 18 or older. 

Limitations

There are a few important limitations to discuss. First, this was an observational study and therefore cannot address cause and effect. In other words, this study does not prove targeting an SBP higher than current recommendations is warranted. The authors are clear that this study should lead to clinical trials to definitively evaluate this relationship. The results of this study definitely support future studies in this area, including clinical trials. 

Nevertheless, this study does suggest the SBP levels that are currently considered normal may lead to negative patient outcomes. Moreover, optimal blood pressure may be higher than what is currently described in the literature. 

Congratulations to the authors on publishing this important work. The best research often leads to more questions. I think it is fair to say that is the case with this study. Further study is needed, including clinical trials.  

Antonio R. Fernandez, PhD, NRP, FAHA, is a research scientist at ESO and serves on the board of advisors of the Prehospital Care Research Forum at UCLA.