Imagist and Acmeist Language

mor-tality in the United States for the past 50 years and is the foremost cause of death among persons aged 1–44.¹² In 2001, 157,078 persons died of acute traumatic injury in the United States—a rate of 55 per 100,000 persons per year. This number is only 6460 fewer than the total number of persons who died from stroke in the same year.⁵⁹ Injury is the most rapidly increasing cause of death in develop-ing countries, resultdevelop-ing from the combination of increased urbanization and motor vehicle use, along with reductions in deaths due to infectious diseases.²³ From the mid-1950s to the mid-1960s, for example, injury fatalities increased 600% in Mexico, 450% in Thailand, 243% in Venezuela, and 200% in Chile.⁸⁹ Proportional mortality rates from injury in Latin America, Asia, Africa, and Oceania range as high as 10%.4,6,9,19,46,60,64,89 For most de-veloping countries, the mortality rate from injury is substantially greater than the rate in the United States.

The exact number or percentage of injury deaths with significant brain involvement is not known but can be estimated using published data. In 2000, for example, the U.S. population was about 275 mil-lion, and various U.S. reports on mortality rates from traumatic brain injury (TBI) range from about 14 to 30 per 100,000 population per year.⁴¹ If the

average mortality rate of 22 per 100,000 from pub-lished U.S. reports is applied to the 2000 U.S.

population, a figure of 60,720 deaths is calculated, representing about 43% of all acute traumatic fa-tal injuries per year.

The objective of this review is to assemble basic epidemiological evidence on brain injury occur-rence, persons at risk, circumstances of exposure, severity and outcomes following injury, and pre-ventive measures using available published ac-counts. For the purposes of this review, the studies selected for evaluation are U.S.-based, published since about 1980, except for an occasional pub-lished account in the foreign literature (or coun-try) to illustrate a substantial difference in finding or an exceptional study.

Methodological Issues in TBI Research While the clinical aspects of brain injury have been widely studied, population-based assessments of TBI are still relatively new and limited, and the methodologies used across the published studies have not yet been completely standardized. A cen-tral issue in comparing findings from earlier reports is the definition of (or criteria for) brain injury used by researchers, a term often used synonymously

with head injury. For research purposes, the for-mer must be considered a subset of the latter.

Many injuries classified by some researchers (e.g., Refs. 2, 20), as head injury or head trauma may or may not include neurological involvement. For example, it is well recognized clinically that skull fracture per se, while a head injury, may not nec-essarily involve trauma to the brain, but skull frac-ture has been used in some studies as a criterion for brain injury study group inclusion.

Another methodological concern in identifying the brain-injured patient is assessment of the ini-tial severity of the injury, which is often the prod-uct of a set of negative rather than positive clinical findings. Another concern in past years is that many less serious brain injuries never come to the atten-tion of a hospital inpatient or outpatient service, and therefore are easily missed by researchers who rely on conventional hospital admission only case-finding methods.²⁴ More recently, however, pa-tients with mild traumatic brain injury (MTBI) are being identified and evaluated epidemiologically.³⁷ Despite this recent focus on emergency depart-ment (ED) patients, a substantial percentage of

“head”-injured persons treated in EDs or admit-ted to hospitals may not have neurological in-volvement.⁴³ In addition, many mildly or trivially brain-injured persons may not seek medical treat-ment or may obtain care through clinics or phy-sicians’ offices.²⁴ This could result in a significant undercount of true brain injuries, mostly those with milder forms of brain trauma. To help cor-rect this situation, researchers from the World Health Organization (WHO )⁸⁷ and the Centers for Disease Control and Prevention (CDC)⁸¹ de-veloped standardized administrative and clinical criteria for traumatic brain injury (TBI), includ-ing MTBI. When fully adopted, these criteria should serve to minimize false-positive and false-negative diagnoses of TBI, especially MTBI.

When research studies are conducted using clinical criteria alone, three factors are critical in differentiating head injury without neurological involvement from brain injury: loss of conscious-ness, posttraumatic amnesia (PTA), and mental disorientation. Brain injuries without cognitive impairment but with vomiting, headaches, and/or dizziness are often diagnosed as concussion.⁶¹ A diagnosis of TBI should include loss of conscious-ness, either at the scene of the injury or later, PTA, or demonstrated mental impairment. Some

stud-ies have considered skull fracture a necessary and sufficient finding.² However, as mentioned above, a significant proportion of skull fractures are not associated with concurrent brain injury, and the positive predictive value of skull fracture for intrac-ranial injury is only about 22%.⁵¹ Even when brain injury is properly defined, population-based ascer-tainment of cases can be difficult. For example, all hospitals or other sources of emergency care in a given study area must be included in the case as-certainment plan, the population base must be known (catchment area counts are not accurate enough), rates must be adjusted for age (and other confounders) if rates are to be compared, and all specific causes of injury must be considered (with both penetrating and blunt causes).20,24,25,40,41,48,86

One form of misclassification of brain injury can occur when deaths that should be attributable to brain trauma are coded to another cause. This may be seen when the deaths are not autopsied or when they are due to multiple severe injuries. Whether brain injury is the primary cause of death or one of several secondary causes, for research purposes the evidence of injury to the brain must be re-corded. Frequently, however, secondary diagnoses of brain injury are often excluded from the hospi-tal record or autopsy report. The extent of this phenomenon in head injury–associated deaths has been examined in a study of multiple-cause-of-death data; findings suggest underestimation of as much as 44%.^41,69,70

Findings from epidemiological studies of brain injury occurrence, risk factors, and outcomes are difficult to compare because of significant dif-ferences both in the lengths of follow-up phases and in the types of patients who are included for follow-up. Additionally, outcome assessments are difficult to interpret when tests of cognitive, psychosocial, or physical outcomes are applied inconsistently.

Mortality and Case Fatality Rates

Slightly over 157,000 U.S. deaths (6.5% of all deaths) were attributed to injury causes in 2001.⁵⁹ If 43% of these deaths were attributable to brain injury (see above), there were approximately 62,830 brain in-jury deaths—an overall brain inin-jury–associated death rate of about 22 per 100,000 per year, a rate which has remained stable over the past two decades.^69,70

Epidemiology of Brain Injury 5 Case fatality rates (CFRs) may be used to

mea-sure extreme outcomes for groups of patients who are admitted to a hospital and diagnosed with brain injury. Reported CFRs obtained from population-based studies vary by a factor of more than 5 among the reports (see Table 1.1).2,20,24–27,40,66,78,85,86 This variation in the data may reflect a combination of differential admission criteria at different treat-ment facilities, differences in severity distributions of patients across hospitals, and differences in the quality of medical management. Ideally, CFRs for various institutions should be compared only after controlling for (1) TBI severity distributions across hospitals; (2) age; (3) comorbid and premorbid conditions; (4) extent and site of injury; and (5) availability of medical care. Data on factors 1, 2, and 4 are easily obtainable and should be used in adjusting CFRs.

Hospital Admissions

The exact number of persons admitted annually to hospitals for brain injury is not known for the United States or for most other countries in which admission statistics are kept. Reasons are similar with respect to death certificate diagnoses; for ex-ample, brain injury may not have been the princi-pal diagnosis and hence may have been listed only after other more severe injuries. One estimate has been derived for the United States using National Hospital Discharge data.⁷⁹ The estimated average

number of TBI admissions for 1994–1995 is about 241,100 persons. The estimating procedure used data on detailed diagnoses and procedures from the U.S. National Hospital Discharge Survey (NHDS) and required selection of appropriate International Classification of Disease (ICD) codes.¹⁸ Investiga-tors at CDC used ICD codes 800.0–801.9, 803.0–

804.9, and 850.0–854.1 to arrive at their estimate of 241,100. Another estimate of annual hospitalized occurrences of TBI⁵³ was derived from the Health-care Cost and Utilization Project (HCUP), operated by the Public Health Service’s Agency for Health-care Research and Quality.⁷³ This inpatient database contains selected demographic, clinical disposition, and diagnostic/procedural information. ICD–9th Revision–Clinical Modification. (ICD-9-CM) diag-nostic codes were examined for each of the 21.5 million persons in the 1998, 1999, and 2000 HCUP datasets, along with age and death in hospital. Pos-sible head injuries were found in 346,000 cases, or 1.6% of total admissions. Within this sample were 31,500 deaths recorded in hospital (a CFR of 9.1 per 100 admissions). The discrepancy between the CDC estimate (241,000) and that from the HCUP (346,000) may be due to a gross difference in case-finding algorithms. It is difficult to imagine that the difference of about 100,000 TBI admissions be-tween the two sources could be accounted for by a 5-year difference in time period. Differences between these values and earlier published esti-mates^41,43 could reflect declines in hospital admis-sions in the 1990s compared with earlier years,

Table 1.1. Traumatic Brain Injury (TBI) Case Fatality Rates (CFRs) from Population-Based U.S. Studies

Location, Year(s) Study

(Reference) Source of Data Group Size CFR 95% CI

Chicago area 1979–80 (86) Hospital/medical examiner records 782 7.9 6.0–9.8

Rhode Island 1979–80 (25) Hospital records 2969 4.9 4.1–5.9

Bronx, NY 1980–82 (20) Hospital/medical examiner records 1209 24.9 23.4–29.4

San Diego Co., CA 1981 (40) Hospital/medical examiner records/death certificates 3359 16.7 15.4–18.0

Seattle 1980–81 (27) Medical center admissions 451 19.0 15.4–22.6

Maryland 1986 (48) Hospital records 5938 4.4 3.9–4.9

Oklahoma 1989 (35) Hospital/medical examiner records 3672 23.0 21.6–25.4

Massachusetts 1990 (66) Hospital/medical examiner records 5778 10.1 9.3–10.9

Colorado 1991–92 (26) Colorado surveillance system 6010 7.6 6.9–8.3

Alaska 1991–93 (85) Alaska trauma registry 2178 5.6 4.6–6.6

Seven states 1994 (78) Hospital records 26, 669 5.6 5.3–5.9

Total U.S. 1994–95 (79) National Hospital Discharge Survey NR 5

NR = not reported.

especially for less seriously injured persons, which in turn may be due in part to changes in health care financing and increasing use of outpatient facilities.

However, among those who are hospitalized and survive, one in five will suffer significant long-term disability.⁴¹

The number of ED-attended head injuries has been estimated in two recent reports.^31,37 In both reports, the data were derived from the Na-tional Hospital Ambulatory Medical Care Survey (NHAMCS) for 1992–1994³¹ and 1995–1996.³⁷ The NHAMCS is a national probability survey of visits to EDs and outpatient departments of non-institutional, general, and short-stay hospitals lo-cated in the 50 states and the District of Columbia.

All diagnoses are coded to the ICD-9-CM, and both reports used the same diagnostic codes:

800.0–801.9, 803.0–804.9, and 850.0–854.1. The estimate of ED/outpatient visits for head injury in 1992–1994 was 1,144,807 (a rate of 444 per 100,000) per year for 1995–96 was 1,027,000 (a rate of 392 per 100,000 per year). A more recent estimate for 1995–2001 provided by the CDC gives an average annual number of ED TBI visits of 1,351,000 or a rate of 403 per 100,000.⁴⁴ These rates are about five to six times higher than the U.S.

estimated hospitalized TBI rate of 85 per 100,000 per year for 1995–2001.⁴⁴ If a conservative aver-age value for ED/outpatient visits (a rate of 400 per 100,000) is added with the TBI hospitalization rate of 85 per 100,000 and the estimated annual TBI

mortality rate of about 18 per 100,000, then an overall annual estimate of 503 per 100,000 popu-lation per year is derived. Applying this rate to the estimated U.S. population in late 2005 of 298 mil-lion yields a total of nearly 1.5 milmil-lion new TBI cases per year of all severities.

Another perspective on brain injury occurrences is provided in Figure 1.1, where hospital discharge rates for the leading neurological conditions are compared. Except for diagnoses of occlusion of cerebral arteries (stroke) and schizophrenia disor-ders, brain injury is a more common diagnosis than hemorrhagic stroke, epilepsy, Alzheimer’s disease, migraine, brain cancer, Parkinson’s disease, and multiple sclerosis.

With all available data, it is then possible to esti-mate the ratios of fatal to nonfatal hospital admis-sions to nonfatal medically treated and released brain-injured persons per year—1:4.4:20; that is, for each fatality there are about 4 or 5 persons hospitalized and about 20 persons are examined and released for a brain injury in the United States each year (Fig. 1.2).

Incidence Studies

Incidence is defined as the number of newly diag-nosed cases in a specified period of time. When such cases occur in a defined (known) population, an incidence rate can be derived. The incidence

Figure 1.1. Brain injury hospital discharge rate compared with rates of 11 leading neurological diagnoses. (Source:

reference 12)

0 Multiple sclerosis Parkinson disease Malignant neoplasm Migraine Alzheimer disease Epilepsy Cerebral degeneration Hemorrhagic stroke Other cerebrovascular disorders Schizophrenic disorders Occlusion of cerebral arteries Brain injury

10 10 12

16 16 19

24 32

72

95

114 87

20 40 60

Rate per 100,000

80 100 120

10 30 50 70 90 110

Epidemiology of Brain Injury 7

group cannot contain previously diagnosed cases, repeat diagnoses by a second physician, or readmis-sion to a health care facility. The incidence rate is a gross approximation of the risk or probability of an event. These parameters probably explain why so few incidence studies of TBI have been attempted.

Since about 1980, only 15 such studies have been attempted for a subset of the U.S. population. Early studies were limited to counties⁴⁰ or cities.^20,86

Methods used for incidence studies have also varied. Some studies ⁴⁰ relied on hospital or coroner record–based case finding using specific dis-charge codes. In addition, the original institu-tional records were reviewed and pertinent data abstracted. Later studies used hospital administra-tive discharge records and electronic file informa-tion for descriptive purposes. In a few instances, a trauma registry was the source of data on TBI.⁸⁵ Figure 1.3 summarizes incidence (and mortality) rates per 100,000 population for these studies.

Using the rate data available from these studies (since about 1980), the average rate of fatal and nonfatal hospitalized TBI is about 140 per 100,000 per year. Excluding the highest reported rate (367/

100,000) and the lowest reported rate (69/100,000) leaves an average U.S. rate of hospitalized (plus im-mediately fatal) TBIs of about 130 per 100,000 per year. These estimates do not include ED-based studies reporting rates of 444 per 100,000, as re-ported by Jager et al.,³⁷ or 392 per 100,000, as re-ported by Guerrero et al.³¹ The rates presented in Figure 1.3 represent three different case-finding methods: (1) hospitalized cases and those identified from medical examiner records (N = 10), (2) only hospital discharge records (N = 3), and (3) trauma registry files (N = 2). Because of this difference in case-finding approaches and other methodological differences, the average rates given here must be used with caution.

External Causes of Brain Injury

Data from many studies (Fig. 1.4) suggest that the most frequent exposure associated with brain injury is transport.1,2,10,20,25,26,31,35,37,40,48,66,78,80,85,86

This category includes riders of automobiles and trucks, bicycles, motorcycles, aircraft, watercraft, and road farm equipment, as well as pedestrians hit by vehicles. The distributions of these external causes can vary significantly across most studies but do illustrate vast differences within general causes.

For example, in the two ED-based studies, the most important exposure reported is falls, com-pared with hospital-based studies, where transport is the most frequent cause of brain injury. In raw numbers, the next most significant single exposure after transport is falls, especially among the very young and the elderly. In many areas of the world, injury from assault is quickly becoming one of the leading causes of brain trauma. Additional significant exposures are sports and recreation.

Misclassifications are likely, however; for example, sports-related events may account for up to 10%

of TBI deaths but might be reported as falls or being struck by an object.⁸⁶

Risk Markers for Brain Injury

Age and Gender

Age groups at highest risk vary, depending on the brain injury level selected for analysis. For ex-ample, the very young (aged 0–4) and the very old Figure 1.2. Number and ratio of brain injury deaths

to nonfatal brain injuries, United States, 2001. ED, emergency department.

1Based on a U.S. brain injury death rate of 22 per 100,000 in 2001

2Based on Centers for Disease Control and Prevention hospital-ized discharge data of 241,000 with any listed traumatic brain injury diagnosis¹³

3Based on reference 37

4Based on reference 78 20.1

Ratio 4.4

1 Deaths

Hospital admitted alive

1,145,000

3

251,000

2

57,078

1

Nonfatal ED treated 80,000–90,000

disabled⁴

(aged 85+) are the two most frequent groups pre-senting to an ED with a brain injury, while those aged 15–25 and over age 65 are most frequently hospitalized. The mortality rates from TBI are high-est after age 76 (Fig. 1.5). The age-specific rate patterns tend to reflect differences in exposure, particularly to motor vehicle crashes and falls.

Males are at greater risk for TBI than females at all ages in all incidence studies. This may reflect differences in risk taking or differential exposure to hazards in specific activities. For example, the male/female rate ratio of TBI due to falls from lad-ders and scaffolds is 28 times higher in males com-pared with females.⁴ Under similar circumstances (i.e., climbing a ladder), females may character-istically elect to use less risky maneuvers than males;

females may also be less likely to be on a ladder in the first place due to sometimes profound dif-ferences in the ratio of the sexes in occupations that normally have such high-risk exposures.

Population-based U.S. studies show that the

incidence rate ratio of TBI varies from 1.4:1 to 2.5:1 in comparing males with females. Mortality gender-specific rate ratios are approximately 3.5:1, strongly indicative of more severe injuries among males.¹

Ethnicity and Socioeconomic Status

Centers for Disease Control data show that Afri-can AmeriAfri-cans have the highest overall injury death rate of any racial/ethnic group in the United States.

In 2000, the injury rate for African Americans was 124.7 per 1000, while the rates for white non-Hispanics (84.6 per 1000), and non-Hispanics (70.0 per 1000) were significantly lower.¹⁴ The excess deaths and injuries may be related to increased exposure to firearms and violence as well as to residential fires, pedestrian injuries, drownings, and spinal cord injuries.⁵⁸ The excess in overall injury rates from all causes or types is also seen in the findings for TBI (Fig. 1.6). For example, the TBI death rate Figure 1.3. Brain injury incidence and fatality rates from selected U.S. studies.

= Mortality rate per 100,000

= Incidence rate per 100,000

* = rate includes hospitalized patients and coroner cases

** = source is trauma registry

† = hospital discharge records only 0

Chicago 1979–1980 [86]

Rhode Island 1979–1980 [24]

Bronx 1980–1982 [20]

San Diego 1981 [42]

Maryland 1986 [48]

Oklahoma 1989 [35]

Massachusetts 1990 [66]

Utah 1990–1992 [80]

Four states 1990–1993 [10]

Colorado 1991–1992 [26]

Alaska 1991–1993 [85]

Seven states 1994 [78]

Total US 1994–1995 [79]

14 states 1997 [44]

Louisiana 1996–1999 [47]

100 200 300

Study location, year(s), [reference]

400 50

25

367*

28

249*

30

180*

30

121*

19

96*

20

108*

23

102*

19

101*

21

130**

92*

5

98*

20 NR NR NR NR

70^† 90*

132^† 152^†

150 250 350

Epidemiology of Brain Injury 9

Figure 1.4. Percent distribution of traumatic brain injury external causes, selected U.S. studies. ED, emergency department.

avalues rounded to whole numbers; hence, percentages may be slightly less or more than 100

bincludes intentional firearms and assaults

cincludes others plus no E-coded available cases

Figure 1.5. Brain injury incidence rates by age group: three U.S. estimates (references 1, 31, 44).

9

0 20 40

Transport Falls Violence^b Other^c

d

Sports Rec.

60 Percent

80 100

10 30 50 70 90

Chicago 1979–1980 [86]

Rhode Island 1979–1980 [24]

Bronx 1980–1982 [20]

San Diego 1981 [42]

Maryland 1986 [48]

Oklahoma 1989 [35]

Massachusetts 1990 [66]

Utah 1990–1992 [80]

Four states 1990–1993 [10]

Alaska 1991–1993 [85]

Seven states 1994 [78]

US EDs 1994–1995 [31]

14 states 1997 [44]

US EDs 1992–1994 [37]

Study location, year(s), [reference]

0–4 15–24 35–44 55–64

Age group

Age group

In document Doctorate Thesis (página 78-84)