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A Prospective Multicenter Study of Patient Factors Associated With Hospital Admission From the Emergency Department Among Children With Acute Asthma
Charles V. Pollack, Jr, MA, MD;
Emily S. Pollack, MD;
Jill M. Baren, MD;
Sharon R. Smith, MD;
Prescott G. Woodruff, MD, MPH;
Sunday Clark, MPH;
Carlos A. Camargo, MD, DrPH;
for the Multicenter Airway Research Collaboration Investigators
Arch Pediatr Adolesc Med. 2002;156:934-940.
ABSTRACT
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Background Recent studies show that objective measures such as peak flow rates
are strongly associated with asthma admission among adults.
Objective To identify factors associated with admission among children.
Methods We performed a prospective cohort study as part of the Multicenter Airway
Research Collaboration. Patients aged 2 to 17 years who presented to the emergency
department (ED) with acute asthma underwent a structured interview in the
ED and another by telephone 2 weeks later. The study was performed at 44 EDs
in 18 US states and 4 Canadian provinces. The decision to admit was made at
the discretion of the treating physician. Univariate analysis of risk factors
for admission was followed by multivariate logistic regression.
Results Of the 1178 eligible subjects, 275 (23%; 95% confidence interval, 21%-26%)
were admitted or placed into ED observation units. A multivariate model that
included 12 characteristics measured at presentation and during the ED stay
was associated with an area under the receiver operating characteristic curve
of 0.91. Demographic factors were not independently associated with admission.
Severity of symptoms (odds ratio, 1.3) and intensity of therapy both before
and during ED visit correlated with the likelihood of admission. Previous
admission for asthma (P = .02) and recent use of
inhaled corticosteroids (P = .04) also were associated
with admission. Peak flows were associated with admission but were infrequently
(23% overall) measured.
Conclusion Hospitalization for asthma exacerbation in children is primarily associated
with clinical indicators in the ED and with historical factors such as previous
asthma admission or intubation, recent use of corticosteroids, and comorbidity.
INTRODUCTION
IN THE UNITED STATES, approximately 5 million children are affected
by asthma,1 and almost 200 000 require
hospital admission every year.2-3
Acute asthma is the most common medical emergency in children, and its incidence
in the pediatric age range is thought to be increasing.3-5
The 10% of children with the most severe asthma account for three quarters
of inpatient treatment days attributed to the disease.6
The final decision regarding whether children with asthma exacerbation can
be adequately treated as outpatients or whether hospitalization is indicated
is often made by emergency physicians. This decision is traditionally based
on a broad constellation of factors; however, there is no consensus on which
factors are important. For example, history and physical examination5, 7-10;
response to therapy in terms of respiratory effort or comfort8, 10-12
and more objective measures such as pulse oximetry9, 12-14
and spirometric9-10,14-15
measurements; quality and availability of outpatient care16-17;
extent of asthma understanding by the caretakers7, 18-19;
ambient air quality and allergen load20-23;
and general socioeconomic factors24 have all
been used by emergency department (ED) and primary care providers. Moreover,
the relative contributions of each of these factors in decision making is
unclear.
During the past decade, consensus panels such as the National Asthma
Education and Prevention Program and the Global Initiative for Asthma have
issued recommendations for the care of the asthmatic patient, both in the
acute and chronic settings.25-27
These guidelines recommend making the admission decision for asthma on the
basis of peak expiratory flow rate (PEFR) or other spirometric testing, coupled
with historical, clinical, and social factors. Previous research indicates
that physicians are only moderately adherent to the recommendations made in
these guidelines.28-33
For pediatric patients, who frequently are unable or unwilling to perform
spirometric maneuvers, these guidelines may not be particularly useful in
the admission decision.
The primary objective of this study was to determine the patient factors
associated with hospital admission among children presenting to the ED with
acute asthma.
PATIENTS AND METHODS
This study combines data from a prospective cohort study performed during
October to December 1997 and April to June 1998, as part of the Multicenter
Airway Research Collaboration.34 Using a standardized
protocol, investigators at 44 EDs in 18 US states and 4 Canadian provinces
provided coverage for 24 hours per day for a median of 2 weeks and enrolled
patients with acute asthma. All patients were treated at the discretion of
the treating physician. Inclusion criteria were physician diagnosis of acute
asthma, age 2 to 17 years, and informed consent of the parent or guardian.
Twenty-five patients who were emancipated minors gave informed consent and
were interviewed. Repeated visits by individual subjects (n = 38) and patients
who were discharged from the ED against medical advice (n = 6) were excluded.
The institutional review board at each of the 44 participating hospitals approved
the study.
DATA COLLECTION
The ED interview assessed patients' demographic characteristics, asthma
history, and details of their current asthma exacerbation. Data on ED management
and disposition were obtained by chart review. All forms were reviewed by
site investigators before submission to the Multicenter Airway Research Collaboration
Coordinating Center in Boston, Mass, where they underwent further review by
trained personnel and then double data entry.
DATA CONVENTIONS
Primary care provider status was assigned on the basis of the following
question: "Do you have a primary care provider (such as a family doctor, pediatrician,
or nurse practitioner)?" If yes, patients were asked to provide the name and
address of their primary care provider. Median family income was estimated
by means of patients' home ZIP codes.35-36
Patients aged 12 to 17 years (n = 223) were asked directly about active (ie,
never smoker, past smoker, or current smoker) and passive smoke exposure.
Passive smoke exposure was determined by asking if anyone living with the
patient or seeing the patient on a regular basis ever smoked while in the
same room as the patient. The PEFR is expressed as a percentage of the patient's
predicted value, based on age, sex, weight, and height.37
Pulmonary index (PI) scores were calculated according to respiratory rate,
accessory muscle use, wheezing, and inspiratory-expiratory ratio; based on
a scale of 0 to 3 for each component of the PI, a total was calculated with
a maximum PI of 12.38 "Severe symptoms" during
the preceding 24 hours was assigned to those reporting asthma symptoms "most
of the time" or "severe" discomfort and distress due to their asthma.
STATISTICAL ANALYSIS
All analyses were performed with Stata 5.0 (Stata Corp, College Station,
Tex). Data are presented as proportions (with 95% confidence intervals [CIs]),
means (with SDs), or medians (with interquartile ranges). Imputed values,
calculated with the Stata impute command, were used to calculate the PI score
when 1 of the elements was missing; patients missing more than 1 value were
not assigned a PI score. The association between admission and other factors
was examined with the  2 test, t test,
and Wilcoxon rank sum test, as appropriate. Variables associated with admission
at P<.1 were evaluated for inclusion in multivariate
logistic regression models. Age and sex were included in the multivariate
model because of their potential clinical significance. All P values are 2-sided, with P<.05 considered
statistically significant.
RESULTS
DEMOGRAPHIC FACTORS
Of 1601 eligible pediatric patients presenting to the ED with acute
asthma, 1184 (74%) were enrolled. Six patients who left against medical advice
were excluded from analysis. Of 1178 analyzed patients, 275 (23%; 95% CI 21%-26%)
were admitted; this includes 22 patients who were placed in an ED observation
unit after the conclusion of ED treatment. (Excluding observation patients
from the admitted cohort in the final regression models did not change the
results.) The median admission rate by site was 20%, with an interquartile
range of 11% to 31%; variability in the overall sample was accentuated by
small numbers of patients at some sites. Age, sex, parental education level,
household income, payer status, and affiliation with a primary care physician
were similar among patients who were admitted and not admitted (Table 1). The possibility of a seasonal variation in admissions
was examined by adjusting for period of enrollment, but this did not materially
affect any of the results that follow (data not shown).
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Table 1. Demographic Characteristics of Patients With Acute Asthma,
According to Admission Status*
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CHRONIC ASTHMA
Chronic asthma history and treatment of admitted patients differed in
some respects from those of patients not admitted (Table 2). Admitted patients were more likely to have been previously
hospitalized for asthma (ever and within 1 year), to have been previously
intubated for asthma, and to have used inhaled corticosteroid (CS) agents
during the preceding month (all P<.05). On the
contrary, age at asthma diagnosis, history of ever having taken systemic CS
therapy, tobacco exposure history, recent ß-agonist use, number of unscheduled
visits, and use of ED services did not differ significantly between the 2
groups.
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Table 2. Chronic Asthma Characteristics of Patients With Acute Asthma,
According to Admission Status*
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ACUTE ASTHMA PRESENTATION
Patients' acute asthma presentation to the ED also differed in several
important areas according to admission status (Table 3). Admitted patients presented most often with a duration
of symptoms of less than a day, but more than 3 hours. They had used more ß-agonists
before ED evaluation. They were more likely to have severe symptoms with the
index episode and several objective markers (respiratory rates, PI scores,
and pulse oximetry measurements) of a more severe exacerbation. Among the
23% of children with PEFR measurements (n = 276), those who were admitted
had lower PEFRs than those who were not admitted. Not surprisingly, younger
patients were less likely to perform PEFR testing: among patients aged 2 to
5 years, only 6% were tested; aged 6 to 11 years, 44%; aged 12 to 13 years,
60%; and aged 14 to 17 years, 69%. Admitted children were also more likely
to have a comorbid condition (eg, pneumonia, pneumothorax, bronchopulmonary
dysplasia) complicating their asthma.
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Table 3. Characteristics of Index Asthma Exacerbation, According to
Admission Status*
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ED COURSE AND DISPOSITION
Characteristics of the patients' ED course are presented in Table 4. Every measured characteristic
was significantly different between patients admitted and not admitted. In
general, these data reflect more intensive therapy during a longer period,
with a lesser response among patients who were admitted after ED care.
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Table 4. Characteristics of ED Treatment and Course for Index Asthma
Exacerbation, According to Admission Status*
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ANALYSIS OF DATA ASSOCIATED WITH ADMISSION
Multivariate analysis of patient factors associated with hospital admission
was performed (Table 5). The PEFR
measurements were not included in the model because these values were recorded
in a nonrepresentative minority of subjects (23%). The explanatory power of
the final logistic regression model was assessed by developing a receiver
operating characteristic curve to evaluate the degree to which the model captured
factors that relate to a patient's risk of admission (Table 5). The area under the receiver operating characteristic curve
generated by the final model was 0.91, which suggests that the model captures
a large proportion of factors that increase a patient's likelihood of admission.
The estimates did not materially change when factors related to admission
among adult patients (eg, having a high school education, estimated household
income, insurance status, having a primary care provider, nebulizer as most
helpful route for administering asthma medication, and asthma medications
other than ß-agonists and inhaled CSs)39
were added to the final model (data not shown).
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Table 5. Association of Patient Factors With Hospital Admission in
Multivariate Logistic Regression*
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COMMENT
This prospective, multicenter study examined pediatric acute asthma
presentations to North American EDs. This is the largest study of its kind
to evaluate admissions for acute asthma and factors associated with these
admissions. Recent data from Multicenter Airway Research Collaboration studies
in adult patients indicate that PEFR measurement is the single best predictive
factor of admission for acute asthma exacerbation.39
Many pediatric patients are unable or unwilling to perform PEFR testing; this
measurement, therefore, is much less helpful in younger age groups. In the
current study, only 23% of patients had PEFR measured, and the youngest patients
were least well represented.
Where performed, however, PEFR was associated with the likelihood of
admission (Table 3). Other factors
clearly associated with admission that were identified in this analysis included
severity of asthma symptoms at presentation, intensity of home and ED management
(as measured by number of ß-agonist treatments), the presence of a comorbid
condition, and asthma history (previous admission or intubation and CS use).
As would be expected, clinical indicators in the ED (pulse oximetry and PI
score) were also associated with admission, but demographic factors such as
sex and race, which have been predictive of admission among asthmatic adults,39 were not significant in this analysis. Other investigators
have sought to predict the likelihood of pediatric asthma admission from the
ED. This work represents a body of literature separate and distinct from research
on admission patterns in population-based cohorts of asthmatic children, and
much of it was published 10 or more years ago.
In 1990, Kerem et al5 published their
results of a prospective study of 200 children (aged 5.6 ± 3.1 years)
who presented to the ED with acute asthma. On arrival and at disposition,
a clinical score was assigned to each child on the basis of heart rate, respiratory
rate, presence of pulsus paradoxus, severity of dyspnea, accessory muscle
use, and degree of wheezing. The clinical score on disposition was the only
factor predictive of admission. Among the components of the score, degree
of dyspnea was the most reliable predictor. The authors concluded that the
admission decision is based mainly on "careful clinical evaluation."5 This is consistent with our finding that the PI score—the
components of which are respiratory rate, degree of wheezing, inspiratory-expiratory
ratio, and use of accessory muscles38—was
strongly associated with admission.
Newcomb and Akhter15 reported in 1986
that "explicit, quantitative criteria for guiding [emergency room] disposition
of asthma" were needed. Their protocol was based entirely on clinical and
historical criteria, and indicated admission if the response to the first
2 nebulized ß-agonist treatments was "poor." They conceded, however,
the existence of a subset of "frequent visitors" (13% of their patients, who
accounted for 66% of all relapses) for whom this approach might be too conservative.15 It should be noted that this study was published
in 1986, before the proper role of CS therapy for pediatric asthma was well
appreciated.
Skoner and colleagues8 in 1987 sought
to develop a "pediatric predictive index" for asthma admission in 193 ED presentations
among 156 children. The pediatric predictive index was calculated by means
of inspiratory breath sounds, degree of wheezing, and respiratory rates. A
score of zero correctly categorized 95% of admissions, but incorrectly categorized
34% of those who were discharged and did not relapse.8
These variables reflect clinical response to therapy and again are consistent
with the PI score37 used in the current study.
In 1984, Ownby et al10 studied 200 pediatric
ED visits for asthma in patients cooperative with PEFR testing; using discriminant
analysis, they selected the variables that best predicted disposition for
the first 100 cases. These factors were initial PEFR, extent of treatment
in the preceding 24 hours, age at onset of asthma, and number of previous
admissions for asthma. The model was then tested on the next 100 visits. Although
this combination correctly predicted disposition for 82% of the 200 cases,
admission was not well predicted (6 of 18 correct in the first 100 cases and
0 of 15 in the confirmation cohort). The authors attributed the weakness of
the model to the PEFR contribution and concluded that overall clinical status
after treatment was the best predictor of admission.10
Meanwhile, Taylor14 found that the addition
of PEFR data to a management guideline for pediatric asthma improved the accuracy
of dispositions. Schuh et al9 in 1997 studied
120 asthmatic children aged 5 to 17 years who presented to the ED with forced
expiratory volume in 1 second less than 50% of that predicted, and found that
baseline characteristics were not predictive of the need for admission. By
2 hours after initiation of therapy, however, both predicted forced expiratory
volume in 1 second less than 30% and total asthma score (composed of accessory
muscle use, degree of wheezing, and degree of dyspnea) of 6 or greater were
associated with the likelihood of admission.9
Twaddell and coworkers12 in 1996 sought
to determine whether a single assessment at the time of presentation could
predict ultimate ED disposition. Children were assigned to 1 of 3 groups:
those probably able to manage at home, those who may need admission, and those
who clearly need admission. Of 53 children, 25 were assigned to the indeterminate
group, clearly limiting the utility of this system. Eighteen of these patients
were admitted.12
In 1994, Geelhoed et al13 evaluated 280
pediatric ED visits for acute asthma. They focused on the potential predictive
ability of the presenting oxygen saturation for "poor outcomes" (admission,
relapse, or need for intravenous aminophylline). Historical factors (age,
age at onset of asthma, number of past admissions, duration of symptoms, and
current and recent treatment) also were considered. Pulse oximetry was found
to be a reliable and independent predictor of poor outcomes. Odds ratios for
a poor outcome were 35 (95% CI, 11-150) for an arterial oxygen saturation
of 91% or less compared with 96% or more, and 4.2 (95% CI, 2.2-8.8) for an
arterial oxygen saturation of 92% to 95% compared with 96% or more.13 This finding is consistent with the current data,
which indicate an odds ratio for admission of 2.2 (95% CI, 1.6-3.0) per 5%
decrease in arterial oxygen saturation.
Taken together, along with the present data, it is apparent that spirometric
data, when available, are valuable to emergency physicians making dispositions
after ED asthma care of children. In children for whom spirometry is not available
or is unreliable, other objective measures such as pulse oximetry and asthma
scoring systems are helpful. Historical factors such as pre-ED treatment,
history of previous endotracheal intubation for asthma, and previous admission
are essential to elicit and record before making a disposition from the ED.
Ultimately, however, perhaps the most reliable factor in this decision is
the intensity of and response to bronchodilator therapy in the ED.
This study has some potential limitations. The EDs participating in
the study typically were in academic medical centers, many of which support
emergency medicine residency programs. Most site investigators had a research
interest in asthma. Thus, these institutions may have been more likely than
nonacademic centers to be familiar with consensus guidelines. In addition,
academic EDs might have different practice and admission patterns than community
hospitals.
Because we did not interview the physicians caring for these patients,
we cannot state with certainty that the various factors found to be associated
with admission actually played a role in the admission decision; the strongest
associations, however, were for clinical indicators that clearly were apparent
to the treating physician in real time. In addition, although we excluded
6 patients who signed out against medical advice from this analysis, we are
aware that patient preferences and other subjective factors that may influence
the decision to hospitalize a patient may not have been captured by our study
design.
CONCLUSIONS
Hospitalization for asthma exacerbation in children is primarily associated
with clinical indicators in the ED and with historical factors such as previous
admission or intubation, use of CSs before the visit, and comorbidity. Although
PEFR is predictive of admission when measured, it frequently cannot be, or
is not, tested in the ED, even in academic EDs staffed by physicians with
a research interest in asthma.
| What This Study Adds
Recent studies show that objective measures such as peak flow rates
are strongly associated with asthma admission among adults. Because determining
peak flow is not always feasible in pediatric patients, we sought to identify
factors associated with admission among children. Demographic factors were
not independently associated with admission. Severity of symptoms (odds ratio,
1.3) and intensity of therapy both before and during ED visit correlated with
the likelihood of admission. Previous admission for asthma (P = .02) and recent use of inhaled corticosteroids (P = .04) also were associated with admission. Peak flows were associated
with admission but were infrequently (33% overall) measured.
In summary, hospitalization for asthma exacerbation in children is primarily
associated with clinical indicators in the ED and with historical factors
such as previous asthma admission or intubation, recent use of corticosteroids,
and comorbidity. More attention to these variables may make disposition more
predictable and consistent.
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AUTHOR INFORMATION
Accepted for publication April 17, 2002.
Dr Woodruff is supported by grant HL-07427, and Dr Camargo by grant
HL-03533, from the National Institutes of Health, Bethesda, Md. The Multicenter
Airway Research Collaboration is supported by grant HL-63253 from the National
Institutes of Health and by unrestricted grants from Glaxo Wellcome Inc (Research
Triangle Park, NC) and Monaghan Medical Corp (Syracuse, NY).
We thank Frank Speizer, MD, for his support, and the Multicenter Airway
Research Collaboration investigators for their ongoing dedication to emergency
airway research.
| The Multicenter Airway Research Collaboration
Steering Committee: Jill M. Baren, MD; Carlos
A. Camargo, Jr, MD (Chair); Rita K. Cydulka, MD; Michael A. Gibbs, MD; Charles
V. Pollack, Jr, MD; Brian H. Rowe, MD.
Operations Committee and Multicenter Airway Research
Collaboration Coordinating Center, Massachusetts General Hospital, Boston: Carlos A. Camargo, Jr, MD (Chair); Sunday Clark, MPH; Leo T. Mayer;
Michael S. Radeos, MD; Caitlin R. Reed, MPhil; Prescott G. Woodruff, MD.
Principal Investigators at the 44 Participating Sites: F. C. Baker III, Maine Medical Center, Portland; J. M. Baren, Hospital
of the University of Pennsylvania, Philadelphia; D. Bond, Grey Nun's Community
Hospital, Edmonton, Alberta; G. W. Bota, Sudbury General Hospital, Sudbury,
British Columbia; E. D. Boudreaux, Earl K. Long Memorial Hospital, Baton Rouge,
La; B. E. Brenner, Brooklyn Hospital Center, Brooklyn, NY; J. Brown, Misericordia
Community Hospital, Edmonton; D. M. Joyce, University Hospital, State University
of New York, Health Sciences Center, Syracuse, NY; C. A. Camargo, Jr, Massachusetts
General Hospital, Boston; K. Camasso-Richardson, Rainbow Babies & Children's
Hospital, Cleveland, Ohio; E. F. Crain, Jacobi Hospital, Bronx, NY; F. Cunningham,
Newark Beth Israel Hospital, Newark, NJ; R. K. Cydulka, MetroHealth Medical
Center, Cleveland; C. O. Davis, University of Rochester Hospital, Rochester,
NY; L. de Ybarrondo, LBJ General Hospital, Houston, Tex; M. A. Dolan, Medical
College of Virginia, Richmond; M. D. Dowd, Children's Mercy Hospital, Kansas
City, Mo; S. D. Emond, St Luke's/Roosevelt Hospital Center, New York, NY;
F. Fairfield, Sturgeon Community Hospital, St Albert, Alberta; T. J. Gaeta,
Methodist Hospital, Brooklyn; M. A. Gibbs, Carolinas Medical Center, Charlotte,
NC; T. E. Glynn, Brooke Army Medical Center, Fort Sam Houston, Tex; T. E.
Glynn, Wilford Hall Medical Center, Fort Sam Houston; R. O. Gray, Hennepin
County Medical Center, Minneapolis, Minn; F. Harchelroad, Allegheny General
Hospital, Pittsburgh, Pa; S. E. Hughes, Albany Medical College, Albany, NY;
L. W. Kreplick, Christ Hospital & Medical Center, Oak Lawn, Ill; S. Lelyveld,
University of Chicago Hospital, Chicago, Ill; A. Mangione, Albert Einstein
Medical Center, Philadelphia; J. S. Mylinski, Richland Memorial Hospital,
Columbia, SC; H. Sedik, Henry Ford Hospital, Detroit, Mich; J. B. Orenstein,
Fairfax Hospital, Falls Church, Va; C. V. Pollack, Jr, Maricopa Medical Center,
Phoenix, Ariz; F. Qureshi, Children's Hospital of the King's Daughters, Norfolk,
Va; M. S. Radeos, Lincoln Medical Center, Bronx; B. H. Rowe, University of
Alberta Hospital, Edmonton; R. J. Scarfone, St Christopher's Hospital for
Children, Philadelphia; D. Schreiber, Stanford University Medical Center,
Stanford, Calif; R. A. Silverman, Long Island Jewish Medical Center, New Hyde
Park, NY; S. Smith, St Louis Children's Hospital, St Louis, Mo; H. Smithline,
Baystate Medical Center, Springfield, Mass; C. A. Terregino, Cooper Hospital/University
Medical Center, Camden, NJ; D. Travers, University of North Carolina Hospitals,
Chapel Hill; A. Walker, Royal Alexandria Hospital, Edmonton.
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Corresponding author: Charles V. Pollack, Jr, MA, MD, Department
of Emergency Medicine, Pennsylvania Hospital, 800 Spruce St, Philadelphia,
PA 19107.
From the Departments of Emergency Medicine, Pennsylvania Hospital,
Philadelphia (Drs C. V. Pollack and E. S. Pollack), Children's Hospital of
Philadelphia (Dr Baren), Washington University School of Medicine, St Louis,
Mo (Dr Smith), and Massachusetts General Hospital and Channing Laboratory,
Department of Medicine, Brigham and Women's Hospital, Harvard Medical School,
Boston, Mass (Drs Woodruff and Camargo and Ms Clark).
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