Patterns in Traumatic Brain Injury Mortality Risk and Outcomes

Traumatic brain injury (TBI) remains a significant cause of mortality in the United States, despite considerable public policy efforts to reduce its incidence as well as improvements in medical care for those who are injured. Each year, nearly two million people sustain head injuries, with annual direct and indirect costs of $48 billion. Deaths from head injuries account for 34 percent of all traumatic deaths. Beginning at age 30, the mortality risk after head injury begins to climb. Persons age 60 and older have the highest death rate after TBI, primarily because of falls, which have a rising incidence in this age group. A better understanding of the factors that affect the epidemiology and survival after TBI is crucial for impacting this major public health problem.

Head injury treatment guidelines were introduced in 1994 to codify the best management practices based on extensive analysis of the existing literature. Many states, including New York, have instituted regional trauma systems with stringent criteria for trauma center designation. During this period, the overall incidence of trauma and TBI decreased, suggesting that preventive efforts may be effective. It is less clear whether these initiatives are effective in improving outcomes. Neurosurgeons and colleagues in general surgery studied changes in TBI epidemiology in New York State between 1991 and 2001 to determine whether there were improved outcome trends. The study, "Changing Patterns of Traumatic Brain Injury Epidemiology and Mortality Risk," will be presented by Deborah L. Benzil, MD, from 5:00 to 5:15 p.m., Monday, April 18, 2005, during the 73rd Annual Meeting of the American Association of Neurological Surgeons in New Orleans. Co-authors of the study are Thomas Mitchell, MD, Stephen DiRusso, MD, PhD, FACS, Thomas Sullivan, BS, and Nanakram Agarwal, MD.

The population for this study was comprised of all patients with ICD-9 codes for TBI in the New York Statewide Planning and Research Cooperative System (SPARCS) database (established in 1979) between January 1, 1991, and December 31, 2001. Age, sex, treating hospital, and year of discharge were recorded for each patient entered into the study. Of the 178,642 patients analyzed, 65 percent were males and 35 percent were females, with a mean age of 39.9 years. The overall mortality rate was 6.1 percent.

The Relative Head Injury Severity Scale (RHISS), which classifies the severity of head injury as none (0), mild (1), moderate (2), and severe (3), was determined for each patient. The Injury Severity Score (ISS), a probability of survival measurement reflecting overall severity of injury, was also calculated and indexed to 2000-2001. For each hospital, the total number of patients treated with moderate and severe head injury was recorded by year.

A stepwise logistical regression (LR) model was developed to predict mortality indexed to TBI mortality in 2001with the following variables: age, sex, RHISS, ISS, and year of discharge. In the second step, hospital TBI volume was added to the LR model. The LR model determined significant predictors of mortality, and odds ratios were calculated for these variables. Area Under the Receiver Operating Characteristic Curve (ROC-Az) was used to evaluate the discrimination of the LR model. Significance of the variables was set at p<0.05. Hospital volume of TBI cases was added as a variable to the LR model (ROC-Az=0.904). The impact of hospital volume on mortality risk was clearly demonstrated. The odds ratio for survival was found to be 1.1 per 100 patients treated by any one hospital. With hospital volume controlled, year of treatment was no longer a significant independent variable.

The mean ISS declined each year from 0.916 in 1991 to 0.881 in 2001. RHISS analysis showed the percentage of mild head injuries decreased from 66.8 percent in 1991 to 42.3 percent in 2001, with a reciprocal increase in moderate and severe head injuries from 33.2 percent to 57.7 percent. The total number of cases of TBI decreased by 33 percent from 20,502 in 1991, to 13,585 in 2001. The ratio of males to females remained constant during the study period, but the average age increased from 35.4 to 44.5. ?Mortality risk for TBI patients in New York State decreased from 1991-2001, despite increases in age and proportion of severe injuries,? stated Dr. Benzil.

The findings of this study show an overall decline in total patients with TBI, a change in TBI patient characteristics, and perhaps most importantly, the significance of hospital TBI volume as a predictor of mortality. While earlier studies showed improved outcomes for people age 75 and older at high volume trauma centers, the importance of these centers has been demonstrated for all patients with TBI. Although mortality may not be directly correlated with other outcome measures, it does represent a quantitative assessment of quality of care. In New York State, the development of the trauma system led to a smaller number of hospitals taking care of a higher volume of patients with TBI, resulting in lower mortality rates. This finding further confirms studies done in general trauma that show improved outcomes in patients treated at certified trauma centers. ?The improved outcomes correlate with the institution of TBI treatment guidelines, the introduction of an organized trauma system in New York State, and federally-mandated legislation for the use of seat belts and air bags in motor vehicles,? said Dr. Benzil.

?The number of people in the United States age 65 or older is expected to double by the year 2030. In looking forward, the increased incidence of head injuries in older patients, along with their increased risk of morbidity and mortality from head injuries, is an important public health concern that we must address, in part through prevention,? added Dr. Benzil.

Founded in 1931 as the Harvey Cushing Society, the American Association of Neurological Surgeons (AANS) is a scientific and educational association with more than 6,800 members worldwide. The AANS is dedicated to advancing the specialty of neurological surgery in order to provide the highest quality of neurosurgical care to the public. All active members of the AANS are certified by the American Board of Neurological Surgery, the Royal College of Physicians and Surgeons (Neurosurgery) of Canada or the Mexican Council of Neurological Surgery, AC. Neurological surgery is the medical specialty concerned with the prevention, diagnosis, treatment and rehabilitation of disorders that affect the entire nervous system, including the spinal column, spinal cord, brain and peripheral nerves.