Commentary: Thoracic Injury in Older Occupants: Challenged Human Crashworthiness
Article Outline
[Ann Emerg Med. 2009;54:295-297.]
According to the US Administration on Aging, the nation's older population (65+ years) totaled 37.9 million in 2007, with a noted increase of 11.2% since 1997. 1 It is estimated that by 2010 and 2020, the US population older than 65 years will be 40 and 55 million, respectively. Currently, there is an overwhelming amount of medical literature that deals with the “graying of America,” largely in its relation to acute and long-term patient-oriented outcomes and medical care expenditures. In the context of emergency medicine, as each year passes, many ED clinical settings across the nation are accurately reflecting this popular metaphor. 2, 3 As a result, emergency physicians are increasingly faced with a very tangible realization of the rapidly growing acute care needs of seniors, 4 coupled with their high degree of vulnerability, particularly in the setting of motor vehicle–related trauma.
In 2006, there were an estimated 30 million older licensed drivers in the United States, and in 2007, 14% of the 41,059 traffic fatalities were older individuals. 5, 6 Despite the greater risk of crash-related injuries for older road users, mobility and transportation remain at the top of issues that optimize the quality of life for older individuals. This was clearly reflected in the 2005 White House Conference on Aging report, in which transportation issues were noted as the third of 50 delegate-adopted priority resolutions to be addressed, superseding resolutions focused on Medicaid Programs for Seniors (fourth) and Medicare Reform for the Future (fifth). 7
This month's issue of NHTSA Notes points to the recent report titled Evaluation of Thoracic Injuries Among Older Motor Vehicle Occupants. 8 The study sets out to describe the relationship between age and the incidence of thoracic injury in motor vehicle crashes. Although it is intuitive to believe that as a person ages he or she might be worse off as a victim of a motor vehicle crash, findings from this report should further heighten clinical awareness of major limitations in the crash-force tolerance of older occupants. These results should also inform behavioral and engineering countermeasures that might enhance occupant protection in seniors, as well as identify steps we can take as emergency physicians to help protect this special group of patients.
Given the magnitude of changes in velocity and indirect and direct blunt forces encountered by older crash victims, trauma care providers must take into consideration the influence of aging on the extent of human tolerance of crash forces. The biophysical changes of aging are remarkably complex; however, in the setting of crash injury these changes are commonly translated into increased bone fragility, considerable limits in cardiovascular and pulmonary plasticity and reserve, and concomitant medical conditions that complicate injuries experienced in a crash. Moreover, coupled with this there are blunted physiologic responses to trauma because of pharmacologic effects that can make the identification of serious injury initially difficult. Herein lies one of the greatest challenges in occupant protection for older drivers and passengers.
The noted NHTSA report studied vehicle occupants (25,752 drivers and occupants) of 4 age groups (25 to 44, 45 to 64, 65 to 74, and 75 years and older [75+]). With little surprise, crash-related thoracic injuries were found to increase with occupant age, with the 75+ age group having the highest proportion of AIS moderate or more severe (2+) thoracic injuries. 9 This held true for this oldest age group irrespective of whether they were driving or riding in any passenger vehicle that crashed and was damaged severely enough to be towed away from the scene. Further, most of the thoracic injuries occurred at substantially lower changes in velocity for the oldest age group than for the younger occupants. Bony thoracic injuries (rib and sternal fractures) were more common for the 65 to 74 and 75+ year age groups, and 20% of the 75+ group sustained lung lacerations and contusion. When the incidence of thoracic injury was assessed for the oldest age group by the type of vehicle they were occupying, larger/heavier vehicles (sports utility vehicles, light trucks, or vans) offered no added protection but instead yielded a higher proportion of thoracic injuries. Some of the more revealing and somewhat counterintuitive findings of this NHTSA study amplify the clinical significance of the aging process in crash injury about the limits of protection offered by restraint use and seating position. Although seatbelt use has a significant protective effect on moderate to severe thoracic injury, the study notes that as age increases, so does the risk of thoracic injury for restrained occupants. Although rear seating positions are generally considered “safer” 10 for the 75+ year age group, rear-seated passengers experienced 18.7% more thoracic injury than same age drivers and front seat occupants. The incidence of thoracic injury increased with occupant age irrespective of the area of the vehicle that had the highest general area of damage (front, side, rear). The direct source of thoracic injury experienced by the study's occupants in a frontal crash was largely attributed to the seatbelt restraint webbing/buckle for the 75+ year age group compared with the steering wheel for all other age group occupants. Finally, the leading cause of death in all of the study age groups was thoracic injury alone or in combination with other body area injuries.
It is no secret to emergency physicians that older drivers and passengers involved in crashes have a greater potential than their younger counterparts to die from what may initially be thought to be minor traumatic injury. In light of the study findings, maintaining a high index of suspicion for a life-threatening thoracic injury is a prudent position to take when providing acute trauma care to older crash victims, particularly to those in the oldest age groups. If this is not already an ingrained, routine, and core component of an emergency physician's acute trauma care thought process, then the rapid aging of our nation and the NHTSA report findings should strongly encourage urgent modification of these thought processes. If this still does not lead to a more conservative approach in treating older crash victims, then it can assuredly be said that it is only a matter of time before a rude awakening is encountered and mortality statistics for older crash victims take an even more notable turn for the worse.
Just as there is recognition of remarkable complexity in the biophysical changes of aging, there is a similar complexity in addressing a multitude of factors that moderate older driver and passenger safety, such as fitness to drive, licensure, driving self-regulation, driving cessation, and occupant protection. Clearly there are important behavioral and human factor issues that influence crash injury risk. However, from a primary prevention perspective the NHTSA report more directly points to opportunities for engineering solutions, namely, older occupant–“friendly” restraint devices and vehicle modifications to accommodate integration of advanced restraints while optimizing comfort and routine use.
Another NHTSA study recently explored occupant protection issues among older drivers and passengers across the United States. 11 This study encompassed several focus groups of older occupants, as well as observation and survey of their restraint use. Overwhelmingly, older occupants chose convenience (ease of use) and comfort as the most important characteristics of a restraint system that would get them to use a seatbelt restraint “all the time” in most vehicle seating positions. Motor vehicle and seatbelt manufactures have understood these consumer-desired characteristics for some time, and this has led to the development of 4-point seatbelt systems, as well as seatbelts with integrated airbags (Figure 1, Figure 2). Both of these restraint designs have been made with the goal of optimizing safety (mitigating occupant ejection, secondary impact within the occupant space, and the dispersal of thoracic loading forces on impact) and comfort. Unfortunately, integration of these innovative seatbelt designs into the new vehicle fleet (domestic and nondomestic) has yet to happen. However, some domestic vehicle manufacturers have already unveiled plans to move these seatbelt designs into production for 2010. If this plan does come to fruition and other vehicle manufacturers follow suit, it will likely be several years before these designs have enough fleet penetration to make a considerable influence in the most thoracic injury–vulnerable occupants.
Figure 1.
Four-point seatbelt design.
Figure 2.
Inflatable seatbelt design.
Until this time comes, we must give thoughtful consideration to the changes in crash injury patterns when encountering the older occupant crash victim and maintain a high index of suspicion for underlying serious thoracic injury. Remember that it may well be that what appears to be a simple or minor injury at first glance quickly becomes complex and immediately life threatening in an older patient with little cardiopulmonary reserve and a low injury tolerance threshold. So during your next encounter of an older crash-injured occupant, keep your clinical guard up and judiciously assess the patient, with greater attention to the biophysical changes of aging.
References
- . A Profile of Older Americans: 2008. Washington, DC: US Dept of Health and Human Services; 2008;
- . Increasing rates of emergency department visits for elderly patients in the United States, 1993 to 2003. Ann Emerg Med. 2008;51:769–774
- . The graying of America: the impact of aging baby boomers on emergency departments. Ann Emerg Med. 2008;51:288–290
- . National Hospital Ambulatory Medical Care Survey: 2006 Emergency Department Summary. Hyattsville, MD: National Center for Health Statistics; 2008;National Health Statistics Reports; No. 7
- . Traffic Safety Facts, 2007 Data: Older Population. Washington, DC: US Dept of Transportation; 2008;DOT HS 810 992
- . Traffic Safety Facts, 2007 Data: Overview. Washington, DC: US Dept of Transportation; 2008;DOT HS 810 993
- . 2005 White House Conference on Aging: The Booming Dynamics on Aging, From Awareness to Action. Washington, DC: US Dept of Health and Human Services; 2006;
- . Evaluation of Thoracic Injuries Among Older Motor Vehicle Occupants. Washington, DC: National Highway Traffic Safety Administration, US Dept of Transportation; 2009;DOT HS 811 101
- . The Abbreviated Injury Scale, 1990 Revision. Des Plaines, IL: Association for the Advancement of Automotive Medicine; 1990;
- . The safest seat: effect of seating position on occupant mortality. J Safety Res. 2008;39:433–436
- . Occupant Protection Issues Among Older Drivers and Passengers: Volume 1 Final Report. Washington, DC: National Highway Traffic Safety Administration, US Dept of Transportation; 2008;DOT HS 810 938
Section editors: Mary Pat McKay, MD, MPH; Todd Thoma, MD; Chris Kahn, MD, MPH; Catherine S. Gotschall, ScD
PII: S0196-0644(09)00620-9
doi:10.1016/j.annemergmed.2009.06.009
© 2009 Published by Elsevier Inc.
