We examined emergency department (ED) visits in the NHAMCS database for the years 2002–2006. Administered by the United States Census Bureau, the NHAMCS is an annual survey of hospital ED and outpatient department visits, designed by the National Center for Health Statistics, a Division of the Centers for Disease Control and Prevention. A nationally representative sample of non-institutional, general (medical, surgical, and children's) and short-stay hospitals are randomly selected within geographically defined areas (Primary Sampling Units) after adjustment for size. Data are obtained from samples of geographically defined areas, hospitals within these areas, clinics and EDs within these hospitals, and patient visits within these clinics and EDs, as components of the 4-stage probability design. Visit information is collected during a randomly assigned 4-week reporting period each year by trained staff members at the sampled hospitals with monitoring by NHAMCS field representatives. Data consistency is ensured by processing at a central facility followed by manual checking using a computerized algorithm. Data are collected on approximately 25,000 visits annually to some 600 hospital EDs and outpatient departments. These data are then utilized to derive national estimates.
The NHAMCS dataset is publicly available via the Internet. This study was declared exempt from review by the institutional review board because data are publicly available and de-identified.
In the NHAMCS database up to three diagnoses are recorded as free text for each visit and then centrally coded using the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes. We identified patient visits for concussion in children aged 0 to 19 years using the ICD-9-CM codes for concussion (850.0, 850.1, 850.11, 850.12, 850.2, 850.3, 850.4, 850.5, 850.9).
Although we did examine the ICD-9-CM codes for skull fracture 800.xx-804.xx, head injury, unspecified 959.01, intracranial hemorrhage (851xx to 853xx), other brain injury (854xx) and intracranial injury of other and unspecified nature 854.xx, patients with these diagnoses alone were not included in the analyses of concussion. Our goal was to study concussion in the absence of structural brain injury. Similarly, we could not be sure that patients with some of these diagnoses alone had signs or symptoms of concussion. For example, pediatric patients who are evaluated after a blow to the head, such as toddlers who fall down the stairs, might be diagnosed with “head injury, unspecified 959.01” even if well appearing and symptom free. As we could not be sure that these patients had concussive symptoms, they were excluded. However, patients who were diagnosed with head injury, unspecified 959.01, skull fracture 800.xx-804.xx, or intracranial injury of other and unspecified nature 854.xx, who were also diagnosed with concussion 850.xx were included. We decided a priori to exclude patients diagnosed with concussion and an intracranial hemorrhage, as the signs and symptoms attributable to the hemorrhage would be difficult to distinguish from those attributable to a concurrent concussion. Those diagnosed with concussion and associated non-head injuries (e.g. radius fracture) were included in our analysis.
Facilities are indicated only by a pseudo-identifier in NHAMCS and we therefore used characteristics of the visits to categorize the types of hospitals. Academic hospitals were defined as facilities in which at least 25% of the patients were evaluated by a resident physician. EDs in which 90% or more of all visits (i.e., not only those for head injury) were for patients 19 years of age or younger were classified as pediatric facilities. We examined data on other hospital characteristics including region (Northeast, South, Midwest, and West) and setting (urban and rural).
In addition to type of hospital, we examined the following data: injury intent (unintentional, intentional and unknown), discharge diagnoses, patient demographics (age, sex, race, and ethnicity), use of computed tomography (CT) or magnetic resonance imaging (MRI), patient insurance type (private, Medicaid, self-pay and other), ED visit within prior 72 hours, patient disposition (discharge vs. hospital admission) and whether or not instructions were given to follow-up for further out-patient management. Patient race (White, Black, Asian/Pacific Islander, Native American, other, multiple) and ethnicity (Hispanic or non-Hispanic) were determined based on the observations of hospital personnel, unless it is hospital policy to ask patients directly for this information. This is in accordance with the NHAMCS instructions to record race and ethnicity according to the “hospital's usual practice or based on your knowledge of the patient or from information in the medical record.”
In addition, we created an “associated injuries” variable, defined as the presence of any non-concussion or head injury ICD-9-CM code in the diagnoses. We categorized mechanisms of injury by using the Centers for Disease Control and Prevention-recommended framework for presenting injury morbidity data (12
) and prior grouping schemes described by Bazarian et al including: ‘Motor vehicle trauma’ (E800–E807), motor vehicle traffic accidents (E810–E819), motor vehicle non-traffic accidents (E820–E825) and accidents involving other vehicles not elsewhere classifiable (E848); ‘sports injuries’ included falls during sports (E886.0), accidentally being struck during sports (E917.0) and injuries involving horses (E828).(13
) In addition, we reviewed the patient's verbatim report of cause of injury for each observation to double check the classification scheme.
We collected data regarding the use of CT or MRI, which was available for the years 2003-2006. The NHAMCS case report form indicates only whether CT or MRI was performed. It does not specify the body part imaged. Using the analysis described by Blackwell et al in a prior study of CT utilization, imaging was assumed to be of the head, as the ultimate diagnosis of included patients was “concussion.”(14
) In order to ensure our results were not confounded by imaging of other body parts, the proportion of patients imaged was recalculated after removing admitted patients and those with associated injuries, as these patients were the most likely to have imaging of a body part other than the head.
The NHAMCS case report form directly queries whether or not follow-up for the patient is recommended. Those entries marked “return/refer to physician/clinic for FU” or “follow up with other MD” were categorized as given specific instructions to follow-up, regardless if “return if needed, PRN/appointment” was also checked. All other patients, including those with either “no follow-up planned” or “return if needed, PRN/appointment,” without the specific instructions described previously, were categorized as not given specific instructions to follow-up.
Weights, strata, and primary sampling unit design variables provided by the NHAMCS were used for all analyses. We used descriptive statistics, with appropriate weighting, to account for the survey sampling methodology, using the svy commands available in Stata 10.1 (StataCorp, College Station, TX). Per NHAMCS recommendations, only those queries with at least 30 observations recorded were included in analyses.