The Epidemiology of Critical Care Air Transport Team Operations in Contemporary Warfare

MILITARY MEDICINE, 179, 6:612, 2014 The Epidemiology of Critical Care Air Transport Team Operations in Contemporary Warfare Lt Col Samuel M. Galvagno, USAFR MC SFS* ; Lt Col Joseph J. Dubose, USAF MC FS ; Col Thomas E. Grissom, USAF MC (Ret.)* ; Col Raymond Fang, USAF MC ; Col Richard Smith, USAF MC (Ret.) ; Lt Col Vikhyat S. Bebarta, USAF MC, FS ; Col Stacy Shackelford, USAF MC ; Thomas M. Scalea, MD, FACS, FCCM ABSTRACT Critical Care Air Transport Teams (CCATTs) have evolved as a vital component of the U.S. Air Force s aeromedical evacuation system. Previous epidemiological research in this area is limited. The objective of this commentary is to highlight the importance of obtaining robust epidemiological data regarding patients transported by CCATTs. A limited epidemiological analysis was performed to describe CCATT patients transported during Operation Enduring Freedom and the waning months of Operation Iraqi Freedom. CCATT transports for the calendar year 2011 were examined as recorded in the U.S. Transportation Command Regulating and Command and Control (C2) Evacuation System database. As many as 290 CCATT primary patient transport records were reviewed. Of these, 58.6% of patients had multiple injuries, 15.9% of patients had traumatic brain injury, 7% had acute coronary syndromes, and 24.8% of all transports were for nonbattle-related injuries. The most common International Classification of Disease, 9th Edition, Clinical Modification coded injury was bilateral lower extremity amputation (40%). Explosive blasts were the top mechanism of injury for patients requiring CCAT. The distribution of injuries and illnesses requiring CCAT appear to have changed compared to previous conventional conflicts. Understanding the epidemiology of casualties evacuated by CCATT during modern warfare is a prerequisite for the development of effective predeployment training to ensure optimal outcomes for critically ill and injured warriors. INTRODUCTION Critical Care Air Transport Teams (CCATTs) are an essential component of the United States Air Force (USAF) aeromedical evacuation system, facilitating transportation of critically ill and injured patients. The capability to transport the critically injured patient in the early days after injury has altered the entire structure of the military medical system, minimizing forward deployed medical resources and allowing transfer to definitive care outside the theater of conflict. Understanding the epidemiology of casualties evacuated by CCATT in modern warfare is essential for developing effective predeployment training and choosing the appropriate equipment to ensure optimal outcomes for critically ill and injured warriors. The post Cold War environment was characterized by an increase in the scope and complexity of worldwide military *Divisions of Trauma Anesthesiology, Department of Anesthesiology, Program in Trauma, Shock Trauma Center, University of Maryland School of Medicine, T1R83, 22 South Greene Street, Baltimore, MD 21201. Divisions of Critical Care Medicine, Department of Anesthesiology, Program in Trauma, Shock Trauma Center, University of Maryland School of Medicine, T1R83, 22 South Greene Street, Baltimore, MD 21201. Program in Trauma, Shock Trauma Center, University of Maryland School of Medicine, 22 South Greene Street, Baltimore, MD 21201. Center for Sustainment of Trauma and Readiness Skills (CSTARS), United States Air Force, 22 South Greene Street, Baltimore, MD 21201. kair University, Maxwell Air Force Base, Montgomery, AL 36112-6335. En Route Care Research Center, U.S. Army Institute of Surgical Research, Fort Sam Houston, TX. doi: 10.7205/MILMED-D-13-00474 operations necessitating... an agile medical system that could deploy and redeploy rapidly with a reduced medical footprint. 1 Attaining this capability required an organizational change in the Joint Service casualty management system resulting in the establishment of the USAF CCATT program in 1994. 2 4 These teams are composed of three specially trained critical care providers: a critical care physician, a critical care nurse, and a respiratory therapist. The critical care physicians primary specialty training may be emergency medicine, surgery, anesthesiology, and/or pulmonary medicine, and the nurses may practice in medical, surgical, and/or cardiac intensive care units. CCATTs are tasked to simultaneously manage multiple high-severity casualties, and each team is trained to manage multisystem trauma, burns, shock, respiratory failure, and other serious illnesses and injuries. 4,5 CCATTs are a high-demand, low-density resource designed for utilization within a full spectrum of operations, including disaster response, small-scale contingencies, homeland security, and major theater war. 6 Limited published data exist regarding the epidemiology of patients transported by CCATTs. Mason et al 7 reported on 133 patients transported from Balad Air Base, Iraq, over a 1-year period. One of the startling findings from this study was a high prevalence of burns (21%), considerably higher than the prevalence of 2 to 10% reported in previous wars. 8 In 2009, Bridges and Evers 9 performed the largest retrospective epidemiologic analysis of CCATT patients to date, reporting on 1,418 patients from Operation Iraqi Freedom/ Operation Enduring Freedom (OIF/OEF). This analysis revealed a high prevalence of traumatic brain injuries, soft 612

tissue trauma, and burns. Because of this analysis, several troop surges have occurred, and mortality and morbidity rates have changed. The epidemiology reported in these studies suggests different injury patterns compared to previous wars. This is likely due to the changing nature of contemporary warfare, but may also be because of sampling during different stages in an ongoing armed conflict. As the role of CCATTs evolves, continual refinement of predeployment training is vital. The principal aim of this commentary is to use a limited epidemiological analysis of patients transported by CCATTs during OEF, and during the waning months of OIF to understand the distribution of injuries and illnesses and lessons learned throughout this period of intense operations. An examination of CCATT data has direct implications for clinical training and medical planning for future conflicts. Understanding the concurrent epidemiology of contemporary utilization may affirm current curricula or provide the impetus for revisions in an effort to improve patient outcomes. METHODS The epidemiology of CCATT patients transported during OIF/OEF was examined using a case series study design that included all transports during the calendar year 2011. All CCATT patients had stabilizing treatment in a forwarddeployed medical facility before transport. Definitive treatment was deferred in most cases in accordance with the CCATT paradigm, which is to deliver critically ill patients to definitive care. 6 The primary data source was the U.S. Transportation Command Regulating and Command and Control (C2) Evacuation System (TRAC2ES). TRAC2ES is a web-based system that coordinates the Department of Defense s movement of sick or injured Service members worldwide. For every patient, TRAC2ES contains data regarding primary and secondary diagnosis codes, as categorized according to the International Classification of Disease, 9th Edition, Clinical Modification (ICD-9-CM). The ICD-9- CM is an adaption of the generalized ICD system used for inpatient data and includes additional morbidity data and procedure codes. In the USAF CCATT program, these codes are assigned to the patient in TRAC2ES before transport. In addition, a mandatory text field is required for CCATT patients containing additional information regarding the patient s condition, age, gender, mechanism of injury, and in-flight critical care requirements. TRAC2ES data were only examined for the calendar year 2011. Secondary sources were reviewed and data abstracted to compare injury patterns throughout OEF and OIF. 1,7 10 Descriptive statistics were calculated. Percentages for the leading causes of injuries were calculated and compared. Means (with standard deviation) and medians (with interquartile ranges) were calculated based on the nature of the data. No inferential statistics were performed. All statistical analyses were performed in Stata Version 11.2 (Stata Corporation, College Station, Texas). The University of Maryland School of Medicine Institutional Review Board determined that this research activity qualified as an exempt study and waived additional review. RESULTS Final analysis of 2011 TRAC2ES data identified 396 CCATT patient transports, representing 290 patients after duplicate transports were removed (patients with multiple CCATT transports). Patients were counted twice only if the primary and secondary ICD-9-CM codes differed from the preceding transport. Median age was 25 years (interquartile range: 22 to 33) and casualties were predominantly male (97.6 %). Table I lists the demographics for this cohort. Army (N = 121) and Marine Corps (N = 79) casualties were the most frequently transported. The 15 most common ICD-9-CM diagnoses in 2011 are listed in Table II. One hundred twenty cases had a single ICD- 9-CM diagnosis, whereas the remaining 170 cases had multiple ICD-9-CM diagnoses. The most common ICD-9-CM diagnosis TABLE I. Demographic Information for Casualties Evacuated by CCATTs During 2011 (N = 290) Variables Total (%) Gender Male 283 (97.6) Female 7 (2.4) Service/Status Army 121 (41.7) Marine Corps 79 (27.2) Air Force 6 (2.1) Navy 8 (2.8) Foreign Military 23 (7.9) Civilian Contractors 27 (9.3) Dependents 6 (2.1) Unknown 19 (6.6) Pediatric Patients a 3 (1) a Age < 15. TABLE II. The 15 Most Common ICD-9-CM Diagnoses (N = 290) ICD-9-CM Code Diagnosis Total 897.6 Bilateral Lower Extremity Amputation 40 E991.3 Injury From Bomb Fragments 29 410.9 Myocardial Infarction/Acute 19 Coronary Syndrome 878.0 8 Open Wound to Groin/Testes/Penis 17 805.4 Lumbar Fracture 16 896 Foot Amputation (Unilateral) 14 897 Lower Extremity Amputation 13 887 Hand Amputation 10 821 Femur Fracture 9 805 Cervical Fracture 7 860 Pneumothorax 7 864 Liver Injury 5 896.2 Foot Amputation (Bilateral) 5 821.1 Femur Fracture (Open) 5 860.1 Pneumothorax (Open) 4 613

FIGURE 1. Mechanisms of injury: comparison of data reported previously by Bridges and Evers 9 to 2011 TRAC2ES data. N = 1,418 patients in 2001 2006 and 290 patients in 2011. Toxic exposure includes intentional and accidental drug overdoses and exposure to chemicals. Numbers represent percentages reported. For the 2001 2006 data, the sum of percentages exceeds 100 because of more than one mechanism of action. For the 2011 TRAC2Es data, the sum of percentages is less than 100 due to missing data and a higher prevalence of medical conditions. was bilateral lower extremity amputation (40%). Forty-six cases of traumatic brain injury were reported (15.9%), although reporting for this injury was inconsistent, and ICD-9-CM codes were not reliably reported in the TRAC2ES database. Only two patients (0.7%) with a primary diagnosis of burns were reported. Nineteen cases of acute coronary syndromes, including five ICD-9-CM coded cases of myocardial infarction, were reported, representing 6.6% of the CCATT disease burden. Nine patients with stroke were transported (3.1%). Mechanism of injury patterns in 2011 were compared to previously published data by Bridges and Evers 9 (Fig. 1). Explosive explosions remained the most common cause of injury throughout both the periods, although due to different injury classifications, the number of injuries directly related to fragmentation from improvised explosive devices (IEDs) in 2011 was likely underreported in TRAC2ES. One hundred twenty-five subjects were injured by an IED explosion (43%), of which 87 (66%) occurred while patients were reported to be dismounted from vehicles. Sixty-seven CCATT patients injured by IEDs (53.6%) required lower extremity amputations; 37 of these amputations were bilateral (55.2%). In 2001 2006, only 29 of 1,491 CCAT patients (1.9%) had severe bilateral lower extremity amputations. These data were also compared to a study by Belmont et al 11 that reported the epidemiology of orthopedic injuries during OIF/OEF from 2001 to 2009. During surge operations in OIF from 2006 to 2007, 54% of all soldiers sustained a musculoskeletal injury. Although Belmont et al 11 did not describe CCATT patients, the overall incidence of IED-related injuries increased from 38% during 2001 2005 to 78% during 2006 2007. Sixteen patients (5.5%) from 2011 were described as being injured solely by fragmentation. This was a lower figure than reported from Bridges 2001 2006 data, 9 which described an incidence of 28%. Among 132 patients injured by IEDs, 14 (10.6%) had severe perineal wounds. Compared to the mechanism of injury patterns reported for CCATT patients in 2001 2006, the 2011 CCATT patients had a slightly lower proportion of injuries caused by gunshot wounds (15.2% in 2011 compared to 17% in 2001 2006). In 2001 2006, battlerelated injuries represented 90.3% of all injuries that required CCATT transport, whereas in 2011, nearly one quarter of all CCATT transports were for nonbattle-related injuries (N = 72) (Fig. 2). In a smaller single-center study that reported the injury and illness distribution for 133 CCAT patients transported FIGURE 2. Incidence of battle-related and nonbattle-related injuries requiring CCATT transport, 2001 2006 compared to 2011. Data from 2001 to 2006 from Bridges and Evers 9 (N = 1,418); data from 2011 from the TRAC2ES database. 614

from 2005 to 2006, 35% of patients had primary medical diagnoses including acute stroke, congestive heart failure, and myocardial infarction. 7 In the same study, 73% of all trauma patients had injuries from IEDs. These results confirm the existence of changing wounding pattern trends from those encountered in previous conflicts. The prevalence of gunshot wounds has decreased from 65% in World War I, to 35% in Vietnam, to as low as 16% in OIF/ OEF. 11 Among patients requiring CCATT, gunshot wounds were the primary diagnosis for 17% of all CCAT patients in 2001 2006 and 15% in 2011. 9 The lethality of gunshot wounds has also significantly decreased since World War II, Korea, Vietnam, and the initial stages of OEF/OIF. 11 In prior wars, up to 33% of all gunshot casualties died compared to a 4.6% mortality rate in OIF. 11 Because of the prevalence of explosion-related injuries in OIF/OEF, the TRAC2ES text fields were examined for descriptions of pulmonary explosion injuries. These injuries were not reliably reported by ICD-9-CM coding. Patients with lung contusions, pneumothoraxes, or other injuries described as being caused by an explosion were tabulated. Six cases (2.1%) were found in the 2011 TRAC2ES data. Dorlac et al 10 reported that 2 of 11 patients requiring an Acute Lung Rescue Team (ALRT) transport sustained a pulmonary explosion injury from an IED. The TRAC2ES data did not specify ALRT requirements for the 6 patients with explosion lung injuries from IED attacks. Nine CCATT patients in 2011 (3.1%) had a documented diagnosis of acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). The requirement for an ALRT was not described for these patients. Although Bridges and Evers 9 did not describe ALI or ARDS in their study, 24% of all patients with medical disease had a primary pulmonary disease. Dorlac et al 10 reported that 15 of 524 mechanically ventilated patients transported in 2005 2007 had a documented diagnosis of ALI/ARDS (3%). DISCUSSION Over 12 years of conflict in OIF/OEF, the wartime U.S. military medical system has continually evolved as an effective global trauma care system. Improvements in patient mortality have been observed, 12 and a major contributory factor thought to be responsible is early casualty care supported by expeditious long-range aeromedical transport to definitive medical care. 13 Although mortality data across generations are difficult to compare because of changes in weapons, tactics, and personal protection, the improved survival of modern combat casualties must be partially attributed to the USAF CCATT program that facilitates delivery of critical patients to definitive care. 1,4,14 CCATTs demonstrated that multiple critical patients can be safely transported over long distances, while receiving high-level intensive care in an aircraft. 7 Although CCATT missions comprise a small fraction of the patients transported via the USAF aeromedical evacuation system, these transports are a surrogate marker for injury severity, because CCATTs evacuate the sickest of the sick. The epidemiology of CCATT patients in OIF/OEF contrasts with the characteristics of patients seen in previous conventional conflicts. 9 In Vietnam, explosive explosion injuries accounted for 3% of injuries and only 5% of patients sustained multiple injuries. 9 Compared to earlier experiences in OIF/OEF, amputations and IED injuries were more prevalent in 2011. In both OIF and OEF, although the ratio of amputations per number of Service members wounded remained stable (1:29 in Vietnam; 1:28 in OEF and OIF), the ratio of amputations to deaths has fallen drastically from 1:11 in Vietnam to 1:3.9 in OIF and 1:6.4 in OEF. 12 These improvments in patient outcomes likely reflect advances in trauma patient care of which the USAF CCATT program is a contributory factor. Indeed, CCATTs exist as an integral link in the damage control surgery and damage control resuscitation continuum that constitutes the Joint Trauma System. Although in prior conflicts casualty care was confined to resource-intensive forward deployed medical assets, CCATTs have helped revolutionize trauma care by enabling the transport of stabilizing patients out of theater to definitive care, often within 24 to 48 hours. In 2011, more nonbattle-related injuries and illnesses were reported in patients requiring CCATT, as compared to 2001 2006; and, as described by Mason et al s 7 data for 2005 2006, a significant proportion of CCAT missions (35%) over any isolated period may be required for nonbattle-related medical problems. In this study, 24% of all missions were for medical problems. A high proportion (35%) of medical patients was also found in Lairet s recent analysis of 656 CCATT patient movements. 14 This highlights the continued importance of knowledge regarding medical diagnoses, since over one quarter of all CCAT transports are typically requested for this reason. In consideration of the major findings from this and other recent analyses, 14 including injury patterns that have not been as prevalent in prior conflicts or even earlier in OEF, several recommendations are presented. These recommendations identify implementable process improvements to enhance medical care for casualties with critical injuries or illnesses. A need exists for continual epidemiological investigation and dissemination of the results of these studies, regarding the distribution of injuries and illnesses among CCATT patients. There is currently no organized registry of patient data that can be queried to analyze the epidemiology of CCATT patients. Information about CCATT missions is maintained at the CCATT Pilot Unit at the 59th Medical Wing, Lackland Air Force Base, Texas, whose unit conducts a rigorous compliance of clinical care and performance improvement of the CCATTs. However, the Pilot Unit is neither staffed nor has the mission of research or long-term analysis of patient outcomes. In addition, patient care documentation from CCATT missions is accomplished on handwritten flow sheets with additional progress notes as required. 2 The Air Force Medical Service or the 615

Department of Defense, in conjunction with trained epidemiologists and statisticians, should develop a robust database that can facilitate not only future epidemiological studies but also detailed analysis of adverse events and outcomes. These studies will improve patient care for CCATT patients by identifying methods to enhance system performance, inform predeployment training requirements, and recognize patient safety hazards. The results from these studies can be rapidly disseminated to CCATT providers electronically and at the unit level so that providers are able to stay prepared for CCATT deployments. Medical training for care of critically ill casualties requires knowledge about the disease states and injury patterns that are likely to be encountered. Medical personnel need to know what they might be faced with so that they can properly prepare. CCATT members are selected from the most highly specialized members of the USAF medical and nursing corps. With knowledge about the epidemiology and outcomes of critically ill or injured patients in contemporary warfare, rapid adjustments can be made to address deficiencies. Predeployment clinical training can be tailored to meet specifically identified needs in knowledge and skills. CCATT training consists of two intensive 2-week courses building upon the members previous clinical competencies. The majority of this training is focused on understanding the USAF aeromedical evacuation system, aircraft platforms, physiologic changes associated with flight, and familiarization with authorized in-flight medical equipment. 3 Limited time is allocated for reviewing topics related to medical care. In reality, although a highly proficient critical care physician might excel in treating blunt trauma patients in a civilian setting, expertise in treating military burns and explosion injuries might be lacking. Likewise, a nurse working in a neurological intensive care unit might lack familiarity with medical and trauma problems. To date, the U.S. military has partially addressed these issues by deploying specialized CCATT augmentation teams for transporting burns and severe lung injuries. 8,10,15 The question of whether additional augmentation teams should be created for traumatic brain injury or spinal cord trauma patients remains to be answered. It is possible that augmentation teams may not be necessary once the epidemiology of injuries is understood because training plans can be developed to address proficiency issues. An example of how epidemiology can assist CCATT providers with obtaining realistic training has recently been published by McCunn et al. 16 The U.S. Air Force Centers for Sustainment of Trauma and Readiness Skills at the University of Cincinnati and the University of Maryland-Shock Trauma Center (STC) were established to enable USAF medical personnel to rotate in a clinical environment similar to deployed environments in terms of the distribution of diseases and injuries encountered. 17 After retrospectively analyzing data on patient volume, injury severity, mechanism of injury, operative cases, and massive transfusion data from 2006 to 2007 at both the Baltimore STC and the Air Force Theater Hospital in Balad, Iraq, investigators concluded that soft-tissue care represented nearly one quarter of all cases. 16 Predeployment training at a high-volume trauma center like STC is beneficial as the high volume of soft-tissue debridement cases at STC is likely to offer a close approximation of high-energy wound care required in theater. In selected highvolume U.S. trauma centers and civilian hospitals, clinical competence can rapidly be attained to prepare CCATT providers on how to care for critically injured war casualties. Knowledge of CCAT epidemiology can be used to effectively leverage civilian partnerships for the benefit of predeployment readiness training. 17,18 On the basis of the recent epidemiology of injuries and illnesses, providers would be better prepared with advanced coursework offered by national societies. In this study, CCATTs were required for a wide variety of injuries and illnesses, including nearly 25% nonbattle-related injuries and multiple complex medical problems. The current clinical validation process involves at least 4 weeks of hands-on and didactic training. 6 Major curriculum elements are listed in Table III. Many of these curriculum elements are only reviewed for 1 to 2 hours, with a combination of didactics and practical exercises. Few CCATT physicians are board-certified intensivists, and CCATT physician recruitment is aimed at physicians who have critical care knowledge and skills related to their primary medical specialty. Similarly, not all CCATT nurses and respiratory therapists practice in high-volume, highintensity critical care units. Additional formal critical care training with a course such as the Fundamentals of Critical Care Support Course (FCCS) administered by the Society of Critical Care Medicine may help address potential knowledge gaps while providing an opportunity to review basic critical care concepts. The FCCS curriculum introduces important principles in the initial care of critically ill or injured patients to physicians, nurses, and other health care providers who may or may not be currently practicing critical care, but who may care for such patients during early stabilization or during transfer of care to a tertiary center. The TABLE III. Major Curriculum Elements Taught During the Basic and Advanced CCATT Courses (Adapted From Beninati et al. 2 ) Aeromedical Evacuation Doctrine Altitude Physiology Flight Physiology Acute Respiratory Failure Mechanical Ventilation Hemodynamic Monitoring Burn Management Infection Control Trauma Management Management of Medical Patients Infection Control Air Transport Supplies and Equipment Critical Care Pharmacology Crew Resource Management Equipment Testing/Approval Flightline Safety Oxygen Therapy/Systems Equipment Familiarization Aircraft Loading/Configuration Mission Management Documentation of Patient Care Training Exercises 616

course is designed to prepare the nonintensivist for the initial management of the critically ill patient until appropriate definitive critical care is arranged. Although a low incidence of burns was reported in 2011, the prevalence of burn injuries requiring CCAT has previously been much higher. 9 Our data contrast to Bridges and Evers 9 who reported an incidence of 17%. Renz et al 8 also reported a higher incidence of burns in patients throughout 2003 2007. CCATT providers need to be adept at managing burn patients, but in civilian and military peacetime practice, burn patient management is relegated to select specialized centers. One potential solution is to require CCATT providers to complete the Advanced Burn Life Support (ABLS) course administered by the American Burn Association. The ABLS is an 8-hour course designed for physicians, nurses, and other providers who are responsible for the management of a burn patient within the first 24 hours post injury. Major objectives include evaluation of the patient with a serious burn, identification of priorities of treatment, techniques to monitor fluid resuscitation, and how to conduct inter-hospital transfers of seriously injured burn patients. However, the utility of ABLS training for CCATT training may be limited because of the existence of a detailed Joint Theater Burn Care Clinical Practice Guideline that has resulted in documented improvements in patient outcomes. 19 Both the FCCS and the ABLS courses are examples of how training for CCATT providers physicians, nurses, and respiratory therapists alike can be augmented. Both of these courses are low-cost solutions to improve readiness for providers not exposed to clinical conditions likely to be encountered during CCATT missions. Additional training with these courses, or similar critical care training opportunities, may obviate the need for specialized, resource-intensive burn and lung (i.e., ALRT) teams. Outcomes beyond mortality must be studied to evaluate CCATT system performance. Limited data have been published regarding CCATT patient outcomes. CCATTs play an important role in the chain of survival for critically injured and ill casualties, and outcome studies should be focused not only on improvements in survival but also on improvements in quality of life and improved function for survivors. Dismounted complex explosion injuries represent a new injury pattern seen in OIF and OEF; accordingly, quality of life assessments are indicated for the most severely injured individuals to assess the role that CCAT has in improving outcomes. 20 In a report by Lairet et al, 14 656 CCATT patient transports from 2007 to 2008 were reviewed, of which 64.8% were for trauma and 35% were for medical conditions. In this abstract, no deaths were reported, and in-flight adverse events were rare. Little is known about the impact on health-related quality of life (HRQOL). Survivors of major trauma often face severe and prolonged deficits in perceived HRQOL, and there is emerging evidence to suggest that these deficits are of utmost importance for survivors, their families, and society. HRQOL is a subset of quality of life, focuses on the effect of illness and treatment, and draws a line between the facets of life that are primarily health-related, versus those that are not. 21 Longitudinal data analysis techniques should be applied to follow CCATT patients as they recover stateside. CCATT patients should be assessed at different intervals for HRQOL, and assessed for other outcome measures, including return to duty and level of disability. The TRAC2ES database is subject to at least two major epidemiological biases. First, misclassification bias was possible. This type of bias is an information bias and is defined as data inaccuracy due to measurement errors (e.g., ICD-9- CM diagnostic codes). Diagnosis codes are entered by an administrative clerk, with variable input from providers. As a patient advances through several progresive roles of care (i.e., multiple CCAT transports), diagnosis codes may become more accurate as additional advanced diagnostic procedures are performed. Alternatively, some information could also be lost. In an effort to control for this limitation, text fields in TRAC2ES were reviewed for every patient. Several uncoded acute coronary syndromes (N = 19) and strokes (N = 9) were captured within the text fields, and it is possible that other diagnoses were not reported. The type of misclassification bias was likely differential because recording of some diagnostic codes may depend on the level of other variables (i.e., other disease codes). For example, a burn might be missed or underreported because of the existence of other more severe injuries. Nevertheless, a burn is still a significant injury that would only be captured by the actual CCATT mission report, not necessarily by TRAC2ES. A second type of bias, reporting bias, is also likely in TRAC2ES. This type of bias could result in data inaccuracy because patients with severe disease tend to have more complete records, and more diagnostic codes. For patients who appeared more severely injured, the text fields in TRAC2ES proved useful, although the level of clinical information was highly variable. Additional diagnoses for patients with single-system critical illnesses may have been missed. CONCLUSIONS CCATTs enable the USAF aeromedical evacuation system to transport critically ill patients in need of advanced care. Both our limited epidemiological analysis and other recent reports indicate that the distribution of injuries and illnesses requiring critical care appear to have changed in contemporary warfare, as compared to prior conventional conflicts. 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