©
Annals of Advances in Automotive Medicine
Changes in the Severity and Injury Sources of Thoracic Aorta Injuries due to Vehicular Crashes Gabriel Ryb MD MPH, Patricia Dischinger PhD, Timothy Kerns MS, Cynthia Burch MPH, Joseph Rabin, MD and Shiu Ho MS National Study Center for Trauma & EMS, University of Maryland School of Medicine
__________________________________ ABSTRACT – Research using the National Automotive Sampling System-Crashworthiness Data System (NASSCDS) suggested a decreased adjusted risk of thoracic aorta injuries (TAI) for newer vehicles during near-side crashes and an increased adjusted TAI risk during frontal crashes. This study attempted to explore possible explanations of these findings. Adult front seat occupants in the Crash Injury Research and Engineering Network (CIREN) database through June 2012 were studied. TAI cases were compared with remaining cases in relation to crash and vehicular characteristics. TAI cases of later crash year (CY) (2004-2012) were compared to those in earlier CY (1996-2003) in relation to TAI severity (minor, moderate, severe and non-survivable). TAI cases in newer model year (MY) vehicles (1999-2012) were compared to those in older vehicles (1988-98) in relation to injury source (steering wheel, front, left, seat belt, air bag and other or unknown). Analysis was stratified by direction of impact (frontal and near-side) and the use of restraints. The similar TAI severity of earlier and later CY among frontal crashes suggests that the observed changes in the adjusted odds of injury seen in NASS-CDS are not due to an increase in injury detection. The decrease in TAI severity among newer vehicles in near-side crashes of later CY is consistent with a beneficial effect of crashworthiness improvements for this crash configuration. A shift of injury source in frontal crashes from the steering wheel in older vehicles to “front of vehicle structures”, “seat belts” and “unknown and other” in newer vehicles should suggest potential sites for crashworthiness improvements.
__________________________________
prevention will be necessary to further decrease the large number of cases dying of this injury.
INTRODUCTION Thoracic aorta injuries (TAI) are recognized to significantly contribute to vehicular crash mortality. The prevalence of TAI among motor vehicle collision (MVC) fatalities varies between 16% and 35% (Neschis et al 2008, Viano 1983, Texeira et al. 2011). The high lethality of these injuries is evident by the high proportion of TAI fatalities (i.e. 70 to 90%) occurring immediately (Neschis et al 2008, Viano 1983, Texeira et al. 2011). Improved outcomes among those experiencing this injury have been attributed to improvements in trauma systems, critical care and surgical techniques (Neschis et al. 2008, Demetriades et al. 2008, Michetti et al. 2007, Fabian 2009). Nevertheless, given the large number of immediate (i.e. scene) deaths, primary CORRESPONDING AUTHOR: Gabriel E. Ryb, MD, MPH The Charles McC. Mathias Jr. National Study Center for Trauma and EMS, University of Maryland, 110 South Paca Street, 4th Floor, Baltimore, MD, 21201; Email: [email protected]
Despite the expected protective effect of vehicular safety improvements, research using medical examiner data has shown no change in the incidence of TAI deaths from 1993 through 2004 (Schulman 2007). In prior research based on a nationally representative dataset of crashes in the USA [i.e. National Automotive Sampling SystemCrashworthiness Data System (NASS-CDS)], diverging associations between vehicle model year and adjusted TAI risk for frontal and nearside crashes were found (Ryb et al 2012 and Ryb et al in press). In that study, newer vehicles appeared to have a protective effect on the occurrence of TAI in near-side crashes but a detrimental effect on the occurrence of TAI in frontal crashes. While these findings appear to be of both important magnitude and statistical significance, biases due to possible changes in the sensitivity of diagnostic techniques over time and
57th AAAM Annual Conference Annals of Advances in Automotive Medicine September 22-25, 2013
167
Vol 57 • September 2013 limitations of the sampling and analytical methodologies may preclude a proper interpretation of these findings. Therefore, to provide a more accurate understanding, this study seeks to contextualize these findings by 1) studying the changes in the frequency of diagnosis of TAI over time within the Maryland hospital discharge data set, 2) discerning potential influences of increased detection on the diagnosis of TAI within the Crash Injury Research and Engineering Network (CIREN) dataset, and 3) exploring potential changes in vehicular crashworthiness that could explain changes in TAI risk particular to principal direction of impact (frontal and near side). The first hypothesis is that the overall trends of TAI diagnosis within the Maryland hospital discharge data set would not show a decrease over time, similar to the NASS-CDS findings. In assessing the potential influences of better detection on the change of TAI incidence over time, it was assumed that improved detection would translate to a higher proportion of less severe TAI injuries within the CIREN dataset. Then, the second hypothesis is that cases entered into the database during a later period of time would exhibit a larger proportion of less severe injuries. With regard to the potential crashworthiness changes, it was assumed that variations in the distribution of vehicle components associated with TAI (i.e., injury sources) could suggest potential influences of crashworthiness on changes in TAI occurrence. Hence, the third hypothesis is that the vehicular components linked to TAI would be different for newer and older model year vehicles.
patients are admitted annually, primarily for the treatment of fractures, head injuries, and internal injuries. As many as 15 injury diagnoses can be recorded in the database, allowing translation to Abbreviated Injury Scale (AIS) scores and the Injury Severity Score (ISS) to be calculated. The Crash Injury Research and Engineering Network (CIREN) population includes patients admitted to one of six currently participating trauma centers following a motor vehicle crash. Eligible patients for inclusion in CIREN must have been occupants of a newer model year vehicle (< 6 years old) and have sustained a serious injury, defined as at least one Maximum Abbreviated Injury Scale (MAIS) 3+ or two MAIS 2 injuries in two separate body regions. Adult CIREN cases of vehicle model years >1988 through June 2012 were studied. METHODS Thoracic aorta injury (TAI) was defined as any reported injury to the aorta identified using AIS codes 420202.4 through 420299.4 (AAAM 1998). Severity of aortic injuries were based on AIS coding description and categorized as minor, moderate, severe and non-survivable . Injuries were considered minor when involving only the intima (intimal tears) with otherwise no other disruption of the aorta. Moderate injuries were those involving minor superficial lacerations, perforations or punctures, with incomplete circumferential involvement, and blood loss of less than 20% and limited to the mediastinum. Severe injuries were those involving only segmental transections with blood loss limited to the mediastinum but exceeding 20% of blood volume. Finally, non-survivable injuries were those with either complete transections or those with hemorrhage not confined to mediastinum.
Data Sources All of Maryland’s acute care hospitals are mandated to report patient discharge data to the Health Services Cost Review Commission (HSCRC). There is 100% participation among the mandated hospitals. The HSCRC database is entirely automated, once medical records personnel abstract patients’ charts at the time of discharge. Mandatory E-coding in the HSCRC database allows for easy identification of admissions resulting from motor vehicle crashes. Approximately 8,000 motor vehicle crash
168
The Maryland hospital discharge data contain International Classification of Disease (ICD-9) codes, which do not include a metric of severity. Therefore, those codes were translated into AIS using ICD-Map software (MacKenzie 1997). Upon translation, TAI injuries were identified and categorized as described above. The CIREN database contains AIS codes for each injury to the case occupant as assigned by the research team member. Those codes were
©
used to identify and categorize TAI in that data set.
Annals of Advances in Automotive Medicine
RESULTS TAI diagnosis in Maryland
Vehicle model year was categorized as MY
Annals of Advances in Automotive Medicine
Changes in the Severity and Injury Sources of Thoracic Aorta Injuries due to Vehicular Crashes Gabriel Ryb MD MPH, Patricia Dischinger PhD, Timothy Kerns MS, Cynthia Burch MPH, Joseph Rabin, MD and Shiu Ho MS National Study Center for Trauma & EMS, University of Maryland School of Medicine
__________________________________ ABSTRACT – Research using the National Automotive Sampling System-Crashworthiness Data System (NASSCDS) suggested a decreased adjusted risk of thoracic aorta injuries (TAI) for newer vehicles during near-side crashes and an increased adjusted TAI risk during frontal crashes. This study attempted to explore possible explanations of these findings. Adult front seat occupants in the Crash Injury Research and Engineering Network (CIREN) database through June 2012 were studied. TAI cases were compared with remaining cases in relation to crash and vehicular characteristics. TAI cases of later crash year (CY) (2004-2012) were compared to those in earlier CY (1996-2003) in relation to TAI severity (minor, moderate, severe and non-survivable). TAI cases in newer model year (MY) vehicles (1999-2012) were compared to those in older vehicles (1988-98) in relation to injury source (steering wheel, front, left, seat belt, air bag and other or unknown). Analysis was stratified by direction of impact (frontal and near-side) and the use of restraints. The similar TAI severity of earlier and later CY among frontal crashes suggests that the observed changes in the adjusted odds of injury seen in NASS-CDS are not due to an increase in injury detection. The decrease in TAI severity among newer vehicles in near-side crashes of later CY is consistent with a beneficial effect of crashworthiness improvements for this crash configuration. A shift of injury source in frontal crashes from the steering wheel in older vehicles to “front of vehicle structures”, “seat belts” and “unknown and other” in newer vehicles should suggest potential sites for crashworthiness improvements.
__________________________________
prevention will be necessary to further decrease the large number of cases dying of this injury.
INTRODUCTION Thoracic aorta injuries (TAI) are recognized to significantly contribute to vehicular crash mortality. The prevalence of TAI among motor vehicle collision (MVC) fatalities varies between 16% and 35% (Neschis et al 2008, Viano 1983, Texeira et al. 2011). The high lethality of these injuries is evident by the high proportion of TAI fatalities (i.e. 70 to 90%) occurring immediately (Neschis et al 2008, Viano 1983, Texeira et al. 2011). Improved outcomes among those experiencing this injury have been attributed to improvements in trauma systems, critical care and surgical techniques (Neschis et al. 2008, Demetriades et al. 2008, Michetti et al. 2007, Fabian 2009). Nevertheless, given the large number of immediate (i.e. scene) deaths, primary CORRESPONDING AUTHOR: Gabriel E. Ryb, MD, MPH The Charles McC. Mathias Jr. National Study Center for Trauma and EMS, University of Maryland, 110 South Paca Street, 4th Floor, Baltimore, MD, 21201; Email: [email protected]
Despite the expected protective effect of vehicular safety improvements, research using medical examiner data has shown no change in the incidence of TAI deaths from 1993 through 2004 (Schulman 2007). In prior research based on a nationally representative dataset of crashes in the USA [i.e. National Automotive Sampling SystemCrashworthiness Data System (NASS-CDS)], diverging associations between vehicle model year and adjusted TAI risk for frontal and nearside crashes were found (Ryb et al 2012 and Ryb et al in press). In that study, newer vehicles appeared to have a protective effect on the occurrence of TAI in near-side crashes but a detrimental effect on the occurrence of TAI in frontal crashes. While these findings appear to be of both important magnitude and statistical significance, biases due to possible changes in the sensitivity of diagnostic techniques over time and
57th AAAM Annual Conference Annals of Advances in Automotive Medicine September 22-25, 2013
167
Vol 57 • September 2013 limitations of the sampling and analytical methodologies may preclude a proper interpretation of these findings. Therefore, to provide a more accurate understanding, this study seeks to contextualize these findings by 1) studying the changes in the frequency of diagnosis of TAI over time within the Maryland hospital discharge data set, 2) discerning potential influences of increased detection on the diagnosis of TAI within the Crash Injury Research and Engineering Network (CIREN) dataset, and 3) exploring potential changes in vehicular crashworthiness that could explain changes in TAI risk particular to principal direction of impact (frontal and near side). The first hypothesis is that the overall trends of TAI diagnosis within the Maryland hospital discharge data set would not show a decrease over time, similar to the NASS-CDS findings. In assessing the potential influences of better detection on the change of TAI incidence over time, it was assumed that improved detection would translate to a higher proportion of less severe TAI injuries within the CIREN dataset. Then, the second hypothesis is that cases entered into the database during a later period of time would exhibit a larger proportion of less severe injuries. With regard to the potential crashworthiness changes, it was assumed that variations in the distribution of vehicle components associated with TAI (i.e., injury sources) could suggest potential influences of crashworthiness on changes in TAI occurrence. Hence, the third hypothesis is that the vehicular components linked to TAI would be different for newer and older model year vehicles.
patients are admitted annually, primarily for the treatment of fractures, head injuries, and internal injuries. As many as 15 injury diagnoses can be recorded in the database, allowing translation to Abbreviated Injury Scale (AIS) scores and the Injury Severity Score (ISS) to be calculated. The Crash Injury Research and Engineering Network (CIREN) population includes patients admitted to one of six currently participating trauma centers following a motor vehicle crash. Eligible patients for inclusion in CIREN must have been occupants of a newer model year vehicle (< 6 years old) and have sustained a serious injury, defined as at least one Maximum Abbreviated Injury Scale (MAIS) 3+ or two MAIS 2 injuries in two separate body regions. Adult CIREN cases of vehicle model years >1988 through June 2012 were studied. METHODS Thoracic aorta injury (TAI) was defined as any reported injury to the aorta identified using AIS codes 420202.4 through 420299.4 (AAAM 1998). Severity of aortic injuries were based on AIS coding description and categorized as minor, moderate, severe and non-survivable . Injuries were considered minor when involving only the intima (intimal tears) with otherwise no other disruption of the aorta. Moderate injuries were those involving minor superficial lacerations, perforations or punctures, with incomplete circumferential involvement, and blood loss of less than 20% and limited to the mediastinum. Severe injuries were those involving only segmental transections with blood loss limited to the mediastinum but exceeding 20% of blood volume. Finally, non-survivable injuries were those with either complete transections or those with hemorrhage not confined to mediastinum.
Data Sources All of Maryland’s acute care hospitals are mandated to report patient discharge data to the Health Services Cost Review Commission (HSCRC). There is 100% participation among the mandated hospitals. The HSCRC database is entirely automated, once medical records personnel abstract patients’ charts at the time of discharge. Mandatory E-coding in the HSCRC database allows for easy identification of admissions resulting from motor vehicle crashes. Approximately 8,000 motor vehicle crash
168
The Maryland hospital discharge data contain International Classification of Disease (ICD-9) codes, which do not include a metric of severity. Therefore, those codes were translated into AIS using ICD-Map software (MacKenzie 1997). Upon translation, TAI injuries were identified and categorized as described above. The CIREN database contains AIS codes for each injury to the case occupant as assigned by the research team member. Those codes were
©
used to identify and categorize TAI in that data set.
Annals of Advances in Automotive Medicine
RESULTS TAI diagnosis in Maryland
Vehicle model year was categorized as MY
