DISCUSSION

Each year in the United States, more than 70,000 pedestrians are injured in traffic accidents. According to the National Highway Traffic Safety Administration, in 1997 there were more than 77,000 pedestrians injured, of whom 5,307 died.1 On average, this translates to one pedestrian injured every 7 minutes with one death every 100 minutes. Most of these fatalities occur in urban areas, in good weather conditions, and at night. It is estimated that nearly 90% of all pedestrian-auto interactions occur at vehicular speeds less than 30 mph (48 kph).6

Force transmission sustained by pedestrians typically involves three phases: vehicular bumper impact, vehicular hood and windscreen impact, and ground impact.7 The initial bumper impact usually results in lower-extremity injuries. Head and torso injuries occur as the victim strikes the hood and windscreen. Further injuries to the head and torso can occur as one falls from the vehicle to the ground or is accelerated into another object.

The goal of the present study was to examine pedestrian versus motor vehicle accidents stratified by age in a large trauma system. Data were obtained from the Los Angeles County Trauma database, which includes information from 13 trauma centers. Variability of data entry is a potential shortcoming in this study, although an attempt to minimize such inconsistency is made through regular review. In this study, patient injuries were grouped into standard anatomic categories based on the ICD-9 diagnosis and were used for injury profile comparisons. We used only the first four ICD-9 codes abstracted from the database to calculate the number of injuries sustained by each patient. Because patients with multiple injuries may not have the most severe injuries included in the first four ICD-9 diagnoses in our analysis, our data may underestimate the injury severity and the total injuries sustained by each patient. Despite these limitations, this study of 5,000 patients is the largest report of its type.

In general, head and extremity injuries occur most commonly in pedestrian versus motor vehicle accidents, as shown in previous studies2-5,8 and our analysis. This observed pattern reflects initial lower-extremity contact with the bumper and subsequent head impact against the vehicle windshield or the ground. Among children, head injury is more common than lower-extremity injury, probably because of their shorter stature. In contrast, among adults and the elderly, extremity injuries occur more frequently than head injury. Across all age groups, lower-extremity injury occurs more frequently than upper. Our study agrees with previous reports that found that chest and abdominal injuries are relatively less common than either extremity or head and neck injuries.2-4,9,10 Perhaps this is because those with chest11 or abdominal trauma may have sustained more severe injuries and died at the scene.

As with previous studies,2,3,12 injury severity and outcomes were related to age. Patient ISS, days of hospitalization, and ICU stay all increase with age. Pediatric patients consistently had a lower ISS, higher RTS, shorter hospitalization, and a shorter ICU stay than did either adults or the elderly. They were also less likely to require operation. In addition to age, head injury is a factor in patient outcomes. Those with a head injury tend to do poorly.

The overall mortality rate in this study was 7.7% and is in agreement with other published series, in which rates ranged from 6% to 30%.3-5 Our rate is at the lower end of the range and corresponds with a recent pedestrian study of 273 patients showing a mortality rate of 6%.3 Elderly patients had the worst outcomes, with a mortality rate of 27.8%. The adverse effect of age has been studied and reported previously.13,14 In addition to poor physiologic reserve, elderly pedestrians are thought to have slower response times and decreased ability to recognize dangerous situations while walking. Mental confusion and sensory changes such as hearing and visual loss may place elderly pedestrians at a disadvantage.15

A recent prevention effort sponsored by the National Highway Traffic Safety Administration and the Federal Highway Administration focused on applying a "safety zone concept" to reduce accidents involving elderly pedestrians.16 This prevention program entails defining selected zones within a community where the biggest accident problems occur and targeting these locations with specific countermeasures. These measures include engineering improvements such as new signs or signals, improving roadway lighting, distributing posters or flyers to senior centers, targeting enforcement efforts in the zones, and giving training programs and presentations to target populations. Among selected cities in the United States where this program was implemented, older-pedestrian accidents were reduced by more than 46% in targeted zones. By focusing on selected zones rather than an entire community, such a program uses funding in a cost-effective manner.

Alcohol consumption has been suggested as a comorbid factor in major trauma.17 It has also been implicated as a contributing factor in pedestrian versus motor vehicle accidents by impairing vision and evaluation of distance.2 Previous authors have reported that between one-fourth and one-half of motor vehicle victims are intoxicated at the time of impact.4,11,18,19 The relation between alcohol consumption and injury severity and mortality has been variable; some series have shown a correlation20,21 and others have not.5,22 In our study, 325 patients had a documented elevated blood alcohol level. More than 80% were legally intoxicated. Those with blood alcohol detected had a higher ISS, lower RTS, and lower GCS than those without. No difference in mortality rates was observed. In this study, blood alcohol levels were obtained primarily in those patients in whom the physician suspected alcohol use. Some intoxicated patients may not have had their blood level documented. This omission would influence our mortality-rate comparison.

In the present study, the majority of patients had residual disability at discharge. A total of 4% had a permanent handicap and 78% had temporary disability. Most hospital payments were from a state or federal source, and less than one-fifth were from a private group carrier.

In summary, injuries from pedestrian versus motor vehicle accidents have a high rate of morbidity. Those who sustain pedestrian trauma have a distinct injury pattern. Knowledge of the mechanism involved allows timely recognition of the various injuries. The high morbidity rate among children and the elderly mandates continued aggressive and effective prevention efforts.

JACS

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