Evacuation Strategies for U.S. Casualties with Traumatic Brain Injury (TBI) with and without Polytrauma

ABSTRACT

Introduction

According to the Military Health System Traumatic Brain Injury (TBI) Center of Excellence, 51,261 service members suffered moderate to severe TBI in the last 21 years. Moderate to severe TBI in service members is usually related to blast injury in combat operations, which necessitates medical evacuation to higher levels of care. Prevention of secondary insult, and mitigation of the unique challenges associated with the transport of TBI patients in a combat setting are important in reducing the morbidity and mortality associated with this injury. The primary goal of this study was a secondary analysis comparing the impact of time to transport on clinical outcomes for TBI patients without polytrauma versus TBI patients with polytrauma transported out of the combat theater via Critical Care Air Transport Teams (CCATT). Our secondary objective was to describe the occurrence of in-flight events and interventions for TBI patients without polytrauma versus TBI with polytrauma to assist with mission planning for future transports.

Materials and Methods

We performed a secondary analysis of a retrospective cohort of 438 patients with TBI who were evacuated out of theater by CCATT from January 2007 to May 2014. Polytrauma was defined as abbreviated injury scale (AIS) of at least three to another region in addition to head/neck. Time to transport was defined as the time (in days) from injury to CCATT evacuation out of combat theater. We calculated descriptive statistics and examined the associations between time to transport and preflight characteristics, in-flight interventions and events, and clinical outcomes for TBI patients with and without polytrauma.

Results

We categorized patients into two groups, those who had a TBI without polytrauma (n = 179) and those with polytrauma (n = 259). Within each group, we further divided those that were transported within 1 day of injury, in 2 days, and 3 or more days. Patients with TBI without polytrauma transported in 1 or 2 days were more likely to have a penetrating injury, an open head injury, a preflight Glascow Coma Score (GCS) of 8 or lower, and be mechanically ventilated compared to those transported later. Patients without polytrauma who were evacuated in 1 or 2 days required more in-flight interventions compared to patients without polytrauma evacuated later. Patients with polytrauma who were transported in 2 days were more likely to receive blood products, and patients with polytrauma who were evacuated within 1 day were more likely to have had at least one episode of hypotension en route. Polytrauma patients who were evacuated in 2–3 days had higher hospital days compared to polytrauma with earlier evacuations. There was no significant difference in mortality between any of the groups.

Conclusions

In patients with moderate to severe TBI transported via CCATT, early evacuation was associated with a higher rate of in-flight hypotension in polytrauma patients. Furthermore, those who had TBI without polytrauma that were evacuated in 1–2 days received more in-flight supplementary oxygen, blood products, sedatives, and paralytics. Given the importance of minimizing secondary insults in patients with TBI, recognizing this in this subset of the population may help systematize ways to minimize such events. Traumatic Brain Injury patients with polytrauma may benefit from further treatment and stabilization in theater prior to CCATT evacuation.

INTRODUCTION

Traumatic Brain Injury (TBI) is a leading cause of morbidity and mortality.¹ According to the Military Health System (MHS) Traumatic Brain Injury Center of Excellence, 51,261 service members suffered moderate to severe TBI in the last 21 years.² Moderate to severe TBI in service members is usually related to blast injury in combat operations, which necessitates medical evacuation to higher levels of care.^2,3 Prevention of secondary insult, and mitigation of the unique challenges associated with the transport of TBI patients in a combat setting are important in reducing the morbidity and mortality associated with this injury.^4,5 The combat injured are moved on various platforms across the continuum of military care, and the optimal timing of transport and its implications on secondary insult to patients with TBI is poorly understood.⁶

Exposure to altitude during aeromedical evacuation (AE) may impose additional physiologic risk to patients with TBI.^6,7 Events that may be associated with secondary injury in TBI patients were identified at the following rates in an earlier CCATT study: temperature > 99.5°F (61%), sodium levels < 145 mmol/L (46%), partial pressure of oxygen (PaO₂) < 80 mmHg (19%), PCO₂ > 40 mmHg (49%), and systolic blood pressure (SBP) < 110 mm Hg (44%).⁶ Some patients may benefit from delayed evacuation from theater to mitigate potential secondary insults. However, TBI is a heterogeneous injury and some injury patterns may benefit from expedited transport to a higher level of care. The survival of combat-related traumatically injured patients has improved in part due to the use of AE platforms. However, the physiologic effects of AE are not well understood and have the potential to contribute to secondary injury for some patient populations, particularly patients with TBI.^4–6

Prevention of secondary injury and prehospital management of TBI have been studied.^7–12 The goals of treatment should be the prevention of hypoxia, hypocapnia, hypercapnia, and hypotension. Better outcomes are associated with PaO₂ > 90%, SBP > 90 mmHg, and an end-tidal carbon dioxide of 35-40 mmHg.^7–12 There is limited data on whether or not patients with TBI would benefit from delayed evacuation.^6,12 Additionally, the implications of concomitant injuries may necessitate expedited AE to improve overall outcomes. Maddry et al. concluded in patients with moderate to severe TBI, delayed evacuation from the combat theater was associated with improved outcomes.⁶ Our study builds on those findings with a secondary analysis of the same population to further inform evacuation strategies for different types of TBI and when there is associated polytrauma. Clinical interventions may need to vary depending on the etiology and type of brain injury (penetrating vs blunt), and the presence or absence of other concomitant injuries. Clinical care for brain injury in conjunction with other injury types may make decisions for interventions and timing of transport more challenging. Further understanding the implications of these other injuries can help mitigate some of those challenges. Characterizing traumatic brain injury types may further elucidate strategic recommendations for patient movement.

The primary goal of this study was a secondary analysis comparing the impact of time to transport on clinical outcomes for TBI patients without polytrauma, versus TBI patients with polytrauma, transported out of the combat theater via Critical Care Air Transport Teams (CCATT). Our secondary objective was to describe the occurrence of in-flight events and interventions for TBI patients without polytrauma versus TBI with polytrauma to assist with mission planning for future transports.

METHODS

We performed a secondary analysis of a retrospective cohort of patients with TBI who were evacuated out of theater by CCATT from January 2007 to May 2014. Data abstractors collected preflight and in-flight information including, laboratory values, vital signs, procedures, and clinical assessments. Outcomes were obtained from the Department of Defense Trauma Registry (DoDTR). Polytrauma was defined as abbreviated injury scale (AIS) of at least three to another region in addition to head/neck. Time to transport was defined as the time (in days) from injury to CCATT evacuation out of combat theater. We calculated descriptive statistics and examined the associations between time to transport and preflight characteristics, in-flight interventions and events, and clinical outcomes for TBI patients with and without polytrauma. Additional details of methodology have been previously published.⁶ This study was approved by the U.S. Air Force 59th Medical Wing Institutional Review Board.

RESULTS

We reviewed the records of 438 patients transported via CCATT from a Role III facility to Landstuhl Regional Medical Center (LRMC). We categorized patients into two groups, those that had a TBI without polytrauma (n = 179) and those with polytrauma (n = 259). Within each group, we further divided those that were transported on the same day of injury, within 2 days of injury, and 3 or more days of injury.

Most patients were male with a median age of 25 years [IQR 21-30] (Table I). Patients with TBI without polytrauma who were transported within 2 days of injury were more likely to have a penetrating injury, an open head injury, a preflight GCS of 8 or lower, and were more likely to be mechanically ventilated compared to those transported in 3 or more days. Those who had polytrauma and were transported within 1 day were less likely to have received blood products prior to flight compared to those evacuated after 2 days.

Patients with TBI without polytrauma who were evacuated within 2 days of injury were more likely to have been mechanically ventilated and more likely to have received blood products, paralytics and sedation compared to patients with TBI without polytrauma evacuated after 3  days (Table II). TBI patients with polytrauma who were transported in 2 days were more likely to receive blood products than those transported within one day or after 3 or more days.

Patients with polytrauma that were evacuated in 1 day or less were more likely to have had at least one episode of hypotension en route (P = 0.0029) compared to polytrauma with later (2–3 days) evacuations (Table III). Polytrauma patients who were evacuated later (2–3 days) had higher hospital days (P = 0.0008) compared to polytrauma with earlier evacuations (Table IV). There was no significant difference in mortality between the groups.

DISCUSSION

In patients with moderate to severe TBI transported via CCATT, early evacuation was associated with a higher rate of in-flight hypotension in polytrauma patients. Preventing secondary injury, such as hypotension, is important in TBI management and treatment. Transport decisions that may mitigate the risk of secondary insults can have a positive impact on outcomes. Previously, Maddry et al. reported a study targeted to characterize the effects of AE on mortality and secondary injury.⁶ They found that in patients with moderate to severe TBI, delayed AE was associated with lower odds of mortality, ventilation at transfer or discharge, and a higher likelihood of discharge to home and return to duty dispositions. In this study, we further characterize this population to understand the implications of having sustained other injuries in addition to TBI on transport time and need for interventions during en route care.

We found that those with polytrauma were evacuated later and had longer hospital stays than patients with TBI and no polytrauma. Those with polytrauma evacuated earlier may be subject to secondary insult, as those patients with early evacuation and polytrauma were more likely to become hypotensive during the en route care continuum. In Maddry et al., 44% of CCATT patients experienced SBP < 110 mmHg.⁶ Our study is not able to determine whether there is an increase in secondary insults due to early transport or whether these insults would have occurred at the ground intensive care unit (ICU) regardless of transport time. However, TBI patients with polytrauma may benefit from further treatment and stabilization in theater prior to CCATT evacuation.

In 2019, Patel et al. reported on a retrospective case series characterizing TBI in patients from Operation Enduring Freedom. 18.5% of their study population sustained penetrating brain injuries and 41% of their study population sustained comorbid injuries.¹³ In 2011, DuBose et al. compared patients sustaining severe TBI on the battlefield to the civilian population using the National Trauma Data Bank.¹⁴ They found that the patients who sustained a penetrating injury on the battlefield had a higher rate of neurosurgical intervention compared to civilian counterparts. They highlighted the need for further research to understand the optimal treatment of penetrating brain injuries on the battlefield. In our study, 59% of the patients had polytrauma. There were 285 penetrating injuries in our study population. We found that those who had a brain injury with a penetrating injury were more likely to have been evacuated from theater early. Furthermore, we found that those patients with polytrauma that were evacuated earlier were more likely to become hypotensive in flight.

In 2020, Maddry et al. reported on the effects of cabin altitude restriction (CAR) on outcomes in patients with moderate or severe TBI.¹⁰ They found that the groups flown with CAR and those without CAR did not have a significant difference in mortality rates, hospital days, ICU days or ventilator days. In our study, we found patients with a TBI without polytrauma who were evacuated early were more likely to have been on a ventilator and less likely to receive supplemental oxygen, and early evacuations with polytrauma were more likely to have had at least one episode of hypotension en route (P = 0.0029) compared to polytrauma with later evacuation. Anticipating hypotension in this patient population can help develop preventative measures to prevent potential secondary injury in this patient population.

LIMITATIONS

Due to the retrospective nature of our study, we are able to identify associations but not causation. A prospective study may help compliment the data reported to help understand the implications of various injuries and transport times on patients with TBI with or without other injuries. Additionally, the data were extracted from medical records that may have missing data secondary to incomplete documentation, difficulty accessing certain parts of the records, and/or illegibility. Such missing data could have implications on the interpretation of the data in regards to Type I and Type II errors. Furthermore, the combat setting is complex and there are other factors that affect patient transport such as medical specialty availability, availability of transport platforms, availability of resources for medical intervention, and weather conditions. These variables were not described in this study.

CONCLUSION

In patients with moderate to severe TBI transported via CCATT, early evacuation was associated with a higher rate of in-flight hypotension in polytrauma patients. Given the importance of minimizing secondary insults in patients with TBI, recognizing this in this subset of the population may help systematize ways to minimize such events. Furthermore, those who had TBI without polytrauma that were evacuated sooner received more in-flight supplementary oxygen, blood products, sedatives, and paralytics. Critical Care Air Transport Teams can use this data to anticipate and plan for such interventions in patients with TBI, which can help to minimize secondary insults. Furthermore, the data can be used by transport teams to decide if further resuscitation should take place before transport, to minimize in-flight events. Traumatic Brain Injury patients with polytrauma may benefit from further treatment and stabilization in theater prior to CCATT evacuation.

ACKNOWLEDGMENTS

ERCC Pilot Unit (Andre Gholson, RN), provision of patient records; En route Care Research Center nurses, data abstraction.

FUNDING

The study was funded by the Defense Health Agency Research and Development (J-9) - Project # J917EC05.

CONFLICT OF INTEREST STATEMENT

None declared.

REFERENCES

Author notes