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(Chest. 2005;127:1579-1586.)
© 2005 American College of Chest Physicians

Asthma Exacerbations in North American Adults*

Who Are the "Frequent Fliers" in the Emergency Department?

Sharon K. Griswold, MD; Carla R. Nordstrom, MD, MPH; Sunday Clark, MPH; Theodore J. Gaeta, DO, MPH; Michelle L. Price and Carlos A. Camargo, Jr, MD, DrPH

* From the Department of Emergency Medicine Dr. Griswold and Ms. Price), Thomas Jefferson University Hospital, Philadelphia, PA; Department of Critical Care Medicine (Dr. Nordstrom), Mercy Hospital of Philadelphia, Philadelphia, PA; Department of Emergency Medicine (Ms. Clark and Dr. Camargo), Massachusetts General Hospital, Boston, MA; and Department of Emergency Medicine (Mr. Gaeta), Methodist Hospital, Brooklyn, NY.

Correspondence to: Sharon Griswold, MD, 1020 Sansom St, Room 1651, Thompson Building, Philadelphia, PA 19107; e-mail: sharon.griswold{at}jefferson.edu


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Summary
 Appendix
 References
 
Objective: To characterize adult asthma patients according to frequency of emergency department (ED) visits in the past year.

Design: Adults presenting with acute asthma to 83 US EDs underwent structured interviews in the ED and by telephone 2 weeks later.

Results: The 3,151 enrolled patients were classified into four groups: those reporting no ED visits in the past year (27%), one to two visits (27%), three to five visits (25%), and six or more visits (21%). The number of ED visits (NEDV) was associated with older age, nonwhite race, lower socioeconomic status, and several markers of chronic asthma severity (all p < 0.001). NEDV was strongly associated with Medicaid insurance (17% among those with no visits, 22% with one to two visits, 30% with three to five visits, 39% with six or more visits; p < 0.001). NEDV was unrelated to gender or having a primary care provider (PCP). In a multivariate model, independent predictors of high ED use (six or more visits a year) were nonwhite race, Medicaid, other public, and no insurance, and markers of chronic asthma severity. Patients with six or more ED visits accounted for 67% of all prior ED visits in the past year.

Conclusions: High NEDV is associated with characteristics that may help with identification of "frequent fliers" in the ED. A better understanding of these characteristics may advance ongoing efforts to decrease asthma health-care disparities, including differential access to primary asthma care. National guidelines recommend specific ED treatments then referral to a PCP. Although longitudinal care is surely important, attempts to reduce frequent ED asthma visits may be better directed toward more specific preventive and educational needs.

Key Words: asthma exacerbation • demography • emergency medical services • health-care cost • primary care provider • recurrent exacerbation • socioeconomic factors


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Summary
 Appendix
 References
 
Asthma is a chronic inflammatory disease of the airways, and a severe exacerbation commonly necessitates a visit to the emergency department (ED) for relief. In the United States, approximately 11% of adults and 12% of children have received a diagnosis of asthma in their lifetime.12 Despite an increased understanding of the pathogenesis of asthma and improved treatment regimens, morbidity remains high, with a reported prevalence rate in 2003 of 38.7 exacerbations per 1,000 population.3

The complexities surrounding health-care disparities have generated national attention, with asthma-related disparities an important part of the Healthy People 2010 initiative.4 The overarching goals of Healthy People 2010 are to improve quality of life and number of healthy years while eliminating health-care disparities. More specifically, the program also calls for health-care providers to "promote respiratory health through better prevention, detection, treatment, and education efforts."4 Asthma-related ED visits are a specific problem targeted for reduction. Improvements have been made in several of the asthma-related goals, including mortality rates and patient education; however, the number of asthma-related hospitalizations and ED visits remains unacceptably high.5

The ED is increasingly recognized as a major source of asthma care, and asthma was identified by Sun and colleagues6 as an independent risk factor of frequent ED use. Indeed, the > 1.9 million ED visits for acute asthma in 2002 represent a 30% increase in asthma-related ED utilization over a decade.78 In response to the growing number of Americans with asthma, the annual direct and indirect costs of the disease have more than doubled, from $6.2 billion in 1990 to $12.7 billion in 1998.9 Fifty-eight percent of these total costs are due to the direct costs of asthma, which include medications (the largest percentage of direct medical expenditure), hospital-based care, and ambulatory services.9 Interestingly, an analysis from the National Medical Expenditure Survey reported that only about 20% of all asthma patients account for about 80% of the total costs of asthma.910 Many of these "high-cost" patients repeatedly return to hospital EDs for urgent asthma care despite referral to their primary care provider (PCP) or other outpatient, community-based services.

The rising percentage of health-care expenditure, augmented by the large number of asthma-related ED visits, reflects the failure of current measures to manage this patient population. But who are these individuals with frequent ED visits? How can we better understand this specific patient population in order to improve their quality of life and asthma management? Addressing the needs of this patient population might ultimately close the gaps in asthma care disparities, as well as reduce the high cost of asthma care. The purpose of this prospective multicenter analysis is to identify characteristics of asthma patients with a high number of emergency department visits (NEDV) and begin to address these critical questions.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Summary
 Appendix
 References
 
The present analysis combined data from four prospective cohort studies performed during 1996 to 2001, as part of the Multicenter Airway Research Collaboration (MARC). MARC is part of the Emergency Medicine Network (EMNet), a collaboration with > 160 participating EDs.11 Using a standardized protocol, investigators at 83 EDs in 26 US states enrolled patients 24 h/d for a median of 2 weeks. The Institutional Review Board at each of the 83 participating hospitals approved the study, and informed consent was obtained for all participants. All patients were managed at the discretion of the treating physician. Inclusion criteria included a physician diagnosis of acute asthma, age 18 to 54 years, and the ability to give informed consent. Repeat visits within the study period were excluded from the current study.

Data Collection
The ED interview assessed demographic characteristics, asthma history, and details of the current asthma exacerbation, including duration of symptoms, number of inhaled ß-agonist puffs within 6 h of ED arrival, and severity of asthma symptoms. Data on respiratory rate, O2 saturation, peak expiratory flow (PEF), and ED course were obtained by chart review. Follow-up interviews were performed by telephone 2 weeks after the index visit. All forms were reviewed by site investigators before submission to the EMNet Coordinating Center in Boston, where they underwent further review by trained personnel and then double data entry.

Median family income was estimated using home zip codes12 and then standardized to year 2000 US dollars. PCP status was assigned on the basis of the following question: "Do you have a primary care provider (such as a family doctor, internist, or nurse practitioner)?" If yes, patients were asked to provide the name and address of their PCP. Post-ED treatment failure was assigned to patients who reported "severe symptoms" during the preceding 24 h on at least one of two questions (ie, asthma symptoms "most of the time" or "severe" discomfort and distress due to their asthma) or who stated that their asthma was "about the same" or worse than at the time of their ED presentation.

PEF is expressed as percentage of predicted value based on race, age, gender, and height.13 Changes in PEF are expressed as the absolute change in percentage of predicted (eg, an improvement from 40% predicted to 70% predicted would be expressed as a change of 30%).

Statistical Analysis
For the purpose of this analysis, we classified subjects into four ED utilization groups based on their NEDV in the past year. Patients were categorized as no prior use or categories of increasing ED utilization: one to two ED visits, three to five ED visits, and six or more ED visits in the past year. All analyses were performed using statistical software (STATA 7.0; StataCorp; College Station, TX). Data are presented as proportions (with 95% confidence interval [CI]), means (SD), or medians (with interquartile range [IQR]). The association between NEDV during the past year and other factors was examined using {chi}2 test, one-way analysis of variance, and Kruskal-Wallis rank test, as appropriate. Age, sex, race/ethnicity, and PCP status were included in multivariate logistic regression models because of their potential clinical significance. Other variables associated with NEDV at p < 0.10 in univariate analysis were evaluated for inclusion in the multivariate logistic regression model. All odds ratios (ORs) are presented with 95% CI. All p values are two-tailed, with p < 0.05 considered statistically significant.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Summary
 Appendix
 References
 
Of 3,257 asthmatic patients enrolled, 3,151 patients (97%) had data on NEDV and were included in the current analysis. Eight hundred sixty-three patients (27%) reported no prior ED visits, while 843 patients (27%) had one to two visits, 791 patients (25%) had three to five visits, and 654 patients (21%) had six or more visits in the past year. Figure 1 depicts the cumulative number of ED visits during the prior year in each of these four frequency groups. Patients with one to two visits (n = 843) during the past 12 months accounted for 9% of all ED visits, patients with three to five visits (n = 791) accounted for 23% of total visits, and patients with six or more visits (n = 654) accounted for 68% of total visits.



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  		Figure 1. Cumulative number of ED visits during the prior year in each of the frequency groups.

 
Univariate analysis of demographic and chronic asthma factors is shown in Table 1 . Older age and nonwhite race/ethnicity were associated with NEDV during the past year. Markers of socioeconomic status, such as completion of high school education and median household income, were inversely related to NEDV. While patients with Medicaid had higher NEDV, and those with private insurance had lower NEDV, PCP status was not associated with the frequency of ED visits. Gender also was unrelated to NEDV.


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  		Table 1. Demographic and Chronic Asthma Characteristics of Patients with Acute Asthma, According to Number of ED Visits During the Past Year*

 
Patients who frequently use the ED for their asthma exacerbations were more likely to report a history of steroid use, hospitalization for asthma, and intubation for asthma (Table 1). Recent use of inhaled ß-agonists, inhaled corticosteroids, and other asthma medications were positive indicators among patients with more frequent ED use. Patients with more frequent ED visits also were more likely to report the ED as their usual site of care when having an asthma problem, and as their usual source of asthma prescriptions.

Table 2 summarizes the acute asthma presentation and ED course of subjects. The typical patient was at approximately 47 to 50% of their predicted PEF. Those with higher ED use had similar initial PEFs compared to patients with few or no ED visits, but received more inhaled ß-agonists both during the first hour and over the entire ED visit. Patients with high NEDV also were more likely to receive steroid treatments in the ED. While ED length of stay did not differ between groups, patients with a higher NEDV were more likely to be admitted to the hospital. Among patients sent home, systemic corticosteroids were more likely to be prescribed to patients with more ED visits.


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  		Table 2. Acute Asthma Presentation of Patients and ED Course, According to Number of ED Visits During the Past Year*

 
Among patients admitted from the ED, the median hospital length of stay was 3 days, which did not differ between NEDV groups (p = 0.69). Patients with a higher NEDV were more likely to report a relapse event during the 2 weeks following the index visit (10%, 14%, 16%, and 21%, respectively; p < 0.001). Patients who frequently use the ED also were more likely to report an ongoing exacerbation at 2-week follow-up (17%, 23%, 25%, and 40%, respectively; p < 0.001).

Manual stepwise, multivariate logistic regression modeling was performed to assess factors associated with high ED use (Table 3 ). The final model includes age, sex, race/ethnicity, education, insurance status, PCP status, history of hospitalization for asthma, history of intubation for asthma, and recent use of inhaled corticosteroids. While age and sex are not significant predictors of high ED use, whites were less likely to be "high-use" patients. Furthermore, when these factors are controlled, patients with Medicaid insurance were 2.8 times more likely to be very frequent visitors to the ED (p < 0.001). In this ED population, PCP status continued to have no relation with frequency of ED use. By contrast, several measures of chronic asthma severity (eg, history of hospitalization, intubation for asthma, and receiving inhaled corticosteroids during the past 4 weeks) all were independent predictors of frequent ED use.


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  		Table 3. Multivariate Model of Factors Associated with Six or More ED Visits for Asthma During the Past Year

 

   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Summary
 Appendix
 References
 
To our knowledge, this is the first large, multicenter study that characterizes asthma patients who frequently utilize the ED for their asthma care. The data were drawn from > 3,000 patients in 83 US EDs. Based on the diversity of these sites, and similar results from previous smaller-scale studies,1415 we believe that our findings can be generalized to other EDs and may help to identify and target adult asthma patients with very frequent use of the ED for their asthma care.

To date, most clinical research on adult patients evaluated in and discharged from the ED has focused on predicting and then preventing acute asthma relapse (ie, revisiting the ED for the same exacerbation usually within 2 to 4 weeks of the index ED visit). These studies suggested that ED relapse is associated with more frequent visits to the ED within the year prior to the index visit,16 and has been directly related to two factors: difficulty performing usual activities in the month prior to presentation to the ED, and discharge from the ED without achieving 50% PEF.1718 A more recent analysis of acute relapse performed by Emerman and colleagues17 defined relapse as a return to a health-care provider for a nonscheduled urgent or emergent asthma visit within 2 weeks of ED discharge. Factors that predicted relapse were multiple ED visits in past year, use of a home nebulizer, multiple asthma triggers, and an increased duration of asthma symptoms prior to ED presentation.

Acute asthma recurrence, in contrast to relapse, refers to multiple exacerbations over the course of a longer period of time, such as 1 year. A history of recurrent ED visits is not necessarily related to acute treatment failures, though our prior study18 suggests a positive association. Frequent ED visits are more likely related to traditional markers of chronic asthma severity (eg, increased incidence of hospitalizations, prior intubations, use of controller medications) because patients with more severe asthma will, by definition, require more frequent ED care compared to patients with mild disease. Recurrent ED visits therefore has a broader meaning than that conveyed by "relapse," since it better reflects the failure of less costly and (ideally) more prevention-oriented, outpatient asthma care.

Along those lines, ED physicians often presume that "frequent fliers" are victims of our health-care system, those who are uninsured or do not have an identifiable PCP. However, we found that lack of insurance was of only borderline statistical significance as a predictor of NEDV. More interestingly, PCP status was not a significant predictor of NEDV in either univariate or multivariate analyses. Approximately two thirds of patients in each of the four groups had a PCP, and the lack of association was disquieting. This finding should encourage health-care providers and organizations to more critically examine the role of PCPs in solving frequent utilization of the ED for acute asthma. Clearly, primary asthma care is worthwhile and prevents many ED visits. However, among those who are in the ED for asthma, the solution may lie elsewhere. Are the PCPs of this ED population following National Asthma Education and Prevention Program guidelines? If yes, are patients adhering to these recommendations? Are the psychosocial problems of high-utilization groups simply not addressed by the assignment of a PCP? With regard to acute management, are the high-utilization groups not choosing their PCP for acute asthma care, or does their PCP refer them to the ED for most, if not all, exacerbations? It has been demonstrated that asthma education programs for pediatric PCPs resulted in fewer hospitalizations and fewer ED visits.

The lack of association challenges previous studies, suggesting that the assignment of a PCP will decrease the utilization of the ED as a source of urgent care in children.19 In the present study population (ie, adult ED patients), there are other important factors are at play.

The current standard of practice for acute asthma is centered on specific, evidence-based treatments in the ED, and then instruction to seek a follow-up medical appointment within 3 to 5 days.20 In addition, national asthma guidelines recommend, when possible, to schedule such an appointment prior to the patient’s discharge. Although based on expert opinion, and not actual scientific evidence, the recommendation seems quite reasonable. However, the present study and others are beginning to cast doubt on the effectiveness of this approach for this specific patient population. Two recent randomized trials found that facilitation of PCP follow-up to improve asthma care did not yield any significant difference in clinical outcomes.21222324 For example, Baren and colleagues22 were able to demonstrate an increase in PCP follow-up in an ED population receiving free medication, transportation vouchers, and facilitated PCP appointments. However, despite an increase in PCP follow-up, there were no differences in NEDVs, hospitalizations, quality of life, or inhaled corticosteroid use at the end of 1-year follow-up.

What works? Highly focused asthma management programs with easy access to medical providers and medications significantly improved asthma care by decreasing hospital admissions.25 In addition, Zeiger and colleagues26 found that facilitated referral of ED asthma patients to asthma specialists, as compared to generalist physicians, reduced the number of ED visits during the subsequent 6 months. Furthermore, a pediatric asthma educational seminar designed for PCPs that focused on the development of communication, teaching skills, and use of therapeutic medications resulted in fewer hospitalizations and fewer ED visits.27 While longitudinal primary care is surely important for asthma in many people, and has other obvious benefits, PCP status may be less influential to asthma well-being among those who frequently visit the ED. Future studies might further evaluate the effect of facilitated referral to asthma specialists vs PCPs on frequency of ED visits and other clinical and economic outcomes.

Further understanding of the special needs and health-care barriers for this high utilization group is paramount to the success of the goals delineated in the Healthy People 2010 program. As demonstrated by Boudreaux and colleagues,28 race/ethnicity-based deficiencies persist as black and Hispanic asthma patients were more likely to utilize the ED and be admitted to the hospital. Health-care providers and policymakers must begin to understand why high-utilization patients report the ED as their usual source of asthma prescriptions and site for acute asthma care. Two alternative strategies merit study. First, patients with high NEDV warrant further investigation to delineate the challenges and barriers to high-quality care among health-disparate populations. Secondly, the impact of facilitated referral of ED asthma patients to asthma specialists while maintaining long-term overall patient management by the PCP should be investigated. The current data, in conjunction with prior studies, raise concerns about overreliance on "referral to PCP" as an effective response to the problems of this high-risk and expensive asthma population.

Limitations
This study has a few potential limitations. First, history of prior ED use was self-reported and there was no attempt to verify the accuracy of the stated information. It may be that subjects who reported six visits actually had more (or fewer) visits, but we believe the rank order to be accurate and believe that even one to two ED visits per year to be excessive. Another limitation is that we have not analyzed the outpatient management of these patients presenting with acute asthma; for example, we do not know how many received specialized asthma care in the past, and we are unable to evaluate how prior outpatient PCP management relates to the National Asthma Education and Prevention Program guidelines. We have sparse data on compliance with prescribed medications, understanding of disease, and details of the written action plans (if present); these factors probably are associated with frequency of ED use and will require further study. Furthermore, future study might assess the psychosocial problems and barriers to health-care access of this high-utilization group. Finally, one must consider that this study examines only patients who presented to the ED with an acute exacerbation. Since the study is specific to ED patients and not population based, it may not be generalizable to all asthma patients. For example, the value of primary care of asthmatic adults would be considerably less in this population; patients receiving excellent primary asthma care are much less likely to visit the ED, and therefore would be underrepresented in this large cohort. However, since our focus is on the characteristics of frequent visitors to the ED, and the development of strategies to potentially help this patient population, the findings are of direct relevance to our objectives.


   Summary
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Summary
Appendix
 References
 
Patients with high NEDV were more likely to be nonwhite, of lower socioeconomic status, have Medicaid insurance, and have higher chronic asthma severity. Patients with six or more ED visits accounted for 20% of consecutive ED patients with acute asthma, and 68% of all prior ED visits in the past year. National guidelines recommend specific ED treatments followed by referral to PCP, with unclear recommendations about if and when to refer patients to asthma specialists. We found no relation between PCP status and NEDV. Efforts to reduce high ED utilization through provision of a PCP referral may be inadequate for this frequent-flier population. Although longitudinal care is surely important, attempts to reduce frequent ED asthma visits may be better directed toward more specific preventive and educational needs.2029


   Appendix
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Summary
 Appendix
References
 
EMNet Steering Committee
Edwin D. Boudreaux, PhD; Barry E. Brenner, MD, PhD; Carlos A. Camargo, Jr., MD (Chair); Rita K. Cydulka, MD; Theodore J. Gaeta, DO, MPH; and Michael S. Radeos, MD, MPH.

EMNet Coordinating Center
Carlos A. Camargo, Jr., MD (Director); Sunday Clark, MPH; Lisa A. Dubois; Sunghye Kim, MD, MSc; Sarah N. Kunz; Andrea J. Pelletier, MS, MPH; Elizabeth Portnoy; Ilana B. Richman; Ashley F. Sullivan, MS, MPH; all at Massachusetts General Hospital, Boston, MA.

Principal Investigators at the 83 Participating Sites
G. Almond (Metropolitan Hospital Center, New York, NY); G. Almond and D. Feingold (Our Lady of Mercy Medical Center, Bronx, NY); F.C. Baker III (Maine Medical Center, Portland, ME); J.M. Baren (Children’s Hospital of Philadelphia, Philadelphia, PA); J.M. Baren, S. Stahmer (Hospital of the University of Pennsylvania, Philadelphia, PA); J.M. Basior (Buffalo General Hospital, Buffalo, NY); B. Bauman (Oregon Health Sciences University Hospital, Portland, OR); R.S. Benenson (York Hospital, York, PA); C.A. Bethel (Mercy Hospital, Philadelphia, PA); L. Bielory (UMDNJ–University Hospital, Newark, NJ); M.P. Blanda (Akron City Hospital, Akron, OH); E.D. Boudreaux (Earl K. Long Memorial Hospital, Baton Rouge, LA); B.E. Brenner (The Brooklyn Hospital Center, Brooklyn, NY); B.E. Brenner (University of Arkansas for Medical Sciences, Little Rock, AR); K.L. Brewer, J, Gough (East Carolina University School of Medicine, Greenville, NC); K. Brown, D.M. Joyce (University Hospital, SUNY HSC, Syracuse, NY); C.A. Camargo Jr. (Massachusetts General Hospital, Boston, MA); A. Chan, F.E. Vaca (UC Irvine Medical Center, Orange, CA); F.L. Counselman (Sentara Norfolk General Hospital, Norfolk, VA); F. Cunningham, G. Ramalanjaona (Newark Beth Israel Hospital, Newark, NJ); R.K. Cydulka (MetroHealth Medical Center, Cleveland, OH); C.O. Davis, A. Sucov (University of Rochester Hospital, Rochester, NY); L. de Ybarrondo (LBJ General Hospital, Houston, TX); D.J. Dire (University of Oklahoma Medical Center, OK, OK); M.J. Drescher (Hartford Hospital, Hartford, CT); N. El Sanadi (Broward General Hospital, Ft. Lauderdale, FL); S.D. Emond (New York Presbyterian Hospital–NY Weill Cornell Medical Center, NY, NY); S.D. Emond (St. Luke’s/Roosevelt Hospital Center, NY, NY); T.J. Gaeta (Methodist Hospital, Brooklyn, NY); T.J. Gaeta (St. Barnabas Hospital, Bronx, NY); M.A. Gibbs (Carolinas Medical Center, Charlotte, NC); T.E. Glynn (Brooke Army Medical Center, Fort Sam Houston, TX); L.G. Graff IV (New Britain General Hospital, New Britain, CT); R.O. Gray (Hennepin County Medical Center, Minneapolis, MN); K. Greineder, M. Sama (St. Joseph Mercy Hospital, Ann Arbor, MI); S.K. Griswold (Thomas Jefferson University Hospital, Philadelphia, PA); D. Gutglass (Children’s Memorial Hospital, Chicago, IL); J.P. Hanrahan and N. Shapiro (Beth Israel Hospital, Boston, MA); F. Harchelroad (Allegheny General Hospital, Pittsburgh, PA); R. Harrigan (Temple University Hospital, Philadelphia, PA); S.E. Hughes (Albany Medical College, Albany, NY); A.H. Idris (University of Florida College of Medicine, Gainesville, FL); M.E. Johnson (Jackson Memorial Hospital, Miami, FL); K. Jones, E.C. Leibner (Detroit Receiving Hospital, Detroit, MI); L.W. Kreplick (Christ Hospital & Medical Center, Oak Lawn, IL); M. Krueger-Kalinski, B. Snyder (UCSD Medical Center–Hillcrest, San Diego, CA); J.L. Larson, D. Travers (University of North Carolina Hospitals, Chapel Hill, NC); E.C. Leibner, C.V. Pollack Jr. (Maricopa Medical Center, Phoenix, AZ); J. Li (Charity Hospital, New Orleans, LA); L.F. Lobon (Beth Israel Medical Center, New York, NY); J. Madden (Christiana Hospital, Newark, DE); A. Mangione (Albert Einstein Medical Center, Philadelphia, PA); M.F. McDermott (Cook County Hospital, Chicago, IL); D. Morgan, R.M. Rodriguez, P.C. Shukla (University of Texas Southwestern Medical Center, Dallas, TX); J.S. Myslinski (Richland Memorial Hospital, Columbia, SC); E.S. Nadel (Brigham and Women’s Hospital, Boston, MA); R.M. Nowak, H. Sedik (Henry Ford Hospital, Detroit, MI); A. Nyce, C.A. Terregino (Cooper Hospital/University Medical Center, Camden, NJ); J.B. Orenstein (Fairfax Hospital, Falls Church, VA); M.E. Pena (St. John Hospital and Medical Center, Detroit, MI); J. Peters (University of Texas Health Sciences Center at San Antonio, San Antonio, TX); M.S. Radeos (Brookdale University Hospital, Brooklyn, NY); M.S. Radeos (Lincoln Medical Center, Bronx, NY); G. Ramalanjaona (St. Michael’s Medical Center, Newark, NJ); D.J. Robinson (University of Maryland Medical Center, Baltimore, MD); G. Rudnitsky (Allegheny University of the Health Sciences, Philadelphia, PA); R.E. Sapien (University of New Mexico Health Sciences Center, Albuquerque, NM); N. Schiebel (Mayo Clinic, Rochester, MN); D. Schreiber (Stanford University Medical Center, Stanford, CA); R. Schwab (Truman Medical Center, KS City, MO); R.A. Silverman (Long Island Jewish Medical Center, New Hyde Park, NY); H. Smithline (Baystate Medical Center, Springfield, MA); P.E. Sokolove (UC Davis Medical Center, Sacramento, CA); D. Stewart (Bronson Medical Center, Kalamazoo, MI); D.M. Taylor (University of Pittsburgh Medical Center, Pittsburgh, PA); J. Walter (University of Chicago Hospital, Chicago, IL); E.J. Weber (UCSF Medical Center, San Francisco, CA); L. White (Akron General Medical Center, Akron, OH); L. Wilson (PHS/Mount Sinai Medical Center, Cleveland, OH); and J.L. Zimmerman (Ben Taub General Hospital, Houston, TX).


   Acknowledgements
 
We thank the MARC Investigators for their ongoing dedication to emergency airway research.


   Footnotes
 
Abbreviations: CI = confidence interval; ED = emergency department; EMNet = Emergency Medicine Network; IQR = interquartile range; MARC = Multicenter Airway Research Collaboration; NEDV = number of emergency department visits; OR = odds ratio; PCP = primary care provider; PEF = peak expiratory flow

Ms. Clark is supported by grant T32 ES07069 and Dr. Camargo is supported by grant HL63841 from the National Institutes of Health. The cohort studies were supported by unrestricted grants from GlaxoSmithKline (Research Triangle Park, NC).

Received for publication September 23, 2004. Accepted for publication November 9, 2004.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Summary
 Appendix
 References
 

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