PEDIATRICS Vol. 120 No. 4 October 2007, pp. 734-740 (doi:10.1542/peds.2007-0409)
ARTICLE |
Childhood Overweight Increases Hospital Admission Rates for Asthma
Department of Pediatrics, Connecticut Children's Medical Center, Hartford, Connecticut
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ABSTRACT |
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 TOP ABSTRACT METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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OBJECTIVES. Although childhood overweight has been associated with increased hospital lengths of stay for patients with asthma, the possible relationship between overweight and hospital admission for asthma has not been well studied. We hypothesized that overweight children who presented to the emergency department with asthma exacerbations were more likely to be admitted to the hospital than nonoverweight children.
METHODS. A retrospective chart review was conducted of all children who were older than 2 years and presented to the emergency department with an asthma exacerbation in calendar year 2005. Children with chronic medical conditions other than asthma were excluded. Children were classified as nonoverweight (
95% weight-for-age percentile) or overweight (>95% weight for age).
RESULTS. During the study period, there were 884 visits to the emergency department for an asthma exacerbation by 813 children; 238 (27%) were admitted to the hospital, and 33 (4%) were admitted to the ICU. Overall, hospital admission was associated with higher clinical asthma score but not with age, gender, or poverty status (as quantified as home in zip-code areas designated as "impoverished"). Overweight children (n = 202 [23%]) were significantly older (8.5 ± 4.4 vs 7.3 ± 4.3 years) and more likely to live in an impoverished area (37% vs 28%). Presenting clinical asthma score and therapeutic interventions in the emergency department were similar for overweight and nonoverweight children; however, overweight children were significantly more likely to be admitted to the hospital.
CONCLUSIONS. Overweight children who present to the emergency department with acute asthma exacerbations are significantly more likely to be admitted to the hospital than nonoverweight children. This identifies an important area in which childhood overweight has a significant impact on the health of children with asthma.
Key Words: pediatrics • asthma • overweight • hospitalization
Abbreviations: ED—emergency department • MPIS—Modified Pulmonary Index Score • OR—odds ratio • CI—confidence interval
Obesity and overweight are a large and growing public health problem for US children.1–3 The National Health and Nutrition Examination Survey (1999–2002) estimated that 31% of children aged 6 to 19 years in the United States are overweight (as defined by gender-specific BMI for age > 95%).1 In addition, the prevalence of childhood overweight has been increasing steadily since the 1960s.1–3 Along with overweight, the prevalence of childhood asthma is increasing.4,5 Asthma is now the most common chronic illness of childhood, affecting 4% to 8% of all US children.4,5 Acute asthma exacerbations incur significant health care costs and are one of the most common causes of visits to the emergency department (ED).
The concurrent increases in overweight and asthma have led researchers to investigate their possible relationship.6 Some large cross-sectional studies have shown an epidemiologic relationship between overweight and the development of asthma,6–8 whereas others have not.9–12 It has been even more difficult to link overweight with objective indices of asthma severity. Overweight per se is known to induce respiratory symptoms such as dyspnea and wheezing, which can mimic asthma.13 In addition, overweight has not been linked to airway hyperresponsiveness, the hallmark of asthma.12 Thus, the relationship between overweight and asthma is poorly understood.
Few studies have investigated the possible link between severity of asthma exacerbations and overweight. The purpose of this study was to investigate the effect of overweight on the acute asthma exacerbations of children who presented to an ED. Our hypothesis was that overweight children who presented to the ED with asthma exacerbations were more likely to be admitted for additional care than children of normal weight.
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METHODS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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This study was approved by the institutional review board at Connecticut Children's Medical Center, and the criteria for informed consent were waived because of its retrospective nature. We retrospectively examined the medical charts of all children who were between the ages of 2 and 18 years and presented to the ED with physician-diagnosed asthma in calendar year 2005. Children with chronic medical conditions other than asthma, such as bronchopulmonary dysplasia, tracheobronchial malacia, congenital heart disease, and static encephalopathy, were excluded. Patients were identified by medical charts using International Classification of Diseases, Ninth Revision, codes. Charts were reviewed, and data were extracted using a uniform data extraction tool by 3 of the investigators (Dr Carroll, Ms Stoltz, and Ms Raykov). Audits for uniformity were performed by the principal investigator (Dr Carroll).
Children were classified as normal weight (95% weight-for-age percentile) or overweight (>95% weight-for-age percentile) on the basis of gender-specific reference data collected by the National Center for Health Statistics.14 BMI (the ratio of the weight in kilograms to the square of the height in meters) was not calculated because a lack of retrospective height data. Demographics, severity of illness on presentation, types of therapies received, and disposition data were collected. Zip codes were collected as a surrogate for socioeconomic status and compared with economic characteristics from the 2000 US Census. Patients who lived in zip codes with median household incomes below the federal poverty level were defined as living in "impoverished" areas.
The Modified Pulmonary Index Score (MPIS) was used to assess illness severity in this study. Asthma scoring systems are often used in pediatric patients as a measure of severity of illness because of the difficulty in obtaining reliable and reproducible measures of airflow obstruction in critically ill children. This validated scoring system has been shown to be highly reproducible among groups of medical professionals (respiratory therapists, nurses, and physicians) as well as among individuals within each group.15 In the MPIS, 6 different categories are evaluated: (1) oxygen saturation in room air; (2) accessory muscle use; (3) inspiratory-to-expiratory ratio; (4) degree of wheezing; (5) heart rate; and (6) respiratory rate. For each of these 6 measurements or observations, a score of 0 to 3 is assigned, resulting in a minimum possible score of 0 and a maximum possible score of 18. In general, scores of <6 are associated with mild asthma exacerbations, scores of 6 to 10 with moderate asthma exacerbations, and scores of >10 with severe asthma exacerbations.
Treatment for acute asthma exacerbations was delivered according to an established protocol that determined therapy according to the MPIS (Table 1). There were no significant changes in physician, nursing, or respiratory therapist staffing during the study period; neither did hospital or ICU admission criteria change. Patients were admitted to the hospital when (1) their MPIS was 
7 after therapy in the ED or (2) they required supplemental oxygen therapy to maintain saturation at 94%. At the study institution, patients may be treated with continuous albuterol nebulizer treatments on the ward. An ICU consultation was required for patients with MPIS 12 after 2 hours of treatment in the ED. A patient was admitted to the ICU when (1) he or she required bronchodilator therapy of 20 mg/hour of continuous albuterol aerosol, (2) he or she required supplemental oxygen at 40%, and (3) the MPIS was >12.
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Relationships between overweight and outcomes were assessed by using appropriate parametric tests and statistics, including
2 and t tests. Multiple logistic regression analysis was used to estimate the odds for being hospitalized for overweight patients relative to nonoverweight patients adjusting for effects that were attributable to clinically meaningful covariates determined a priori. These variables included age, gender, poverty status, and race/ethnicity. Results were adjusted for covariates and are reported as adjusted odds ratios (ORs) and 95% confidence intervals (CIs). P < .05 was considered statistically significant for all tests. Data were analyzed by using JMP 6.0.2 statistical software (SAS Institute, Cary, NC) and along with statistical consultation from the Office of Research at Connecticut Children's Medical Center. Results are reported as means ± SD or as frequency (%). |
RESULTS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Patient Characteristics
In calendar year 2005, there were 1282 visits to the ED for acute asthma exacerbations. Of these, 395 visits were excluded because the children had chronic medical conditions other than asthma (Fig 1). Three children were excluded for missing weights. Data were analyzed from 884 visits to the ED in 813 children. In 202 (22%) of these visits, the child was overweight. The distribution of weight-for-age percentiles is shown in Fig 2. There was a bell-shaped distribution of the weight-for-age percentiles except at the highest level. Very overweight children (weight-for-age percentile: >97%) composed 18% of the total population and the majority (77%) of the overweight children.
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Only 55% (n = 483) of children had a documented MPIS assessed prospectively on admission. Children who were not admitted to the hospital were significantly less likely to have admission MPIS documented in the medical chart (42% vs 89%; P < .0001). This suggests that children with lower illness severity were less likely to have an MPIS determined by the providers. However, a similar proportion of overweight and nonoverweight children had admission MPIS documented in the medical chart (56% vs 54%; P = .69).
Results According to Disposition
In 238 (27%) of these ED visits, the children were admitted to the hospital and 33 (4%) were admitted to the ICU (Tables 2 and 3). Overall, hospital admission was associated with higher clinical asthma score and overweight but not with age, gender, or poverty status. There was a statistically significant difference in race/ethnicity in these 2 populations, with more white children admitted and more Hispanic children not admitted.
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Children who were admitted to the hospital received more therapies for their asthma exacerbation. These children were more likely to be treated with supplemental oxygen, continuous albuterol therapy, corticosteroids (either intravenous or oral), nebulized ipratropium, and magnesium (Table 3).
Results According to Weight
In 202 (27%) of these ED visits, the children were overweight (Table 3). Overweight children were significantly older and more likely to live in an impoverished area than nonoverweight children. There was a statistically significant difference in race/ethnicity in these 2 populations, with more white children in the nonoverweight population and more black children in the overweight population. Overweight was not associated with gender.
Overweight was not associated with presenting clinical asthma score (MPIS) or with therapies received in the ED (Table 3). Despite similar severity of illness and therapeutic interventions in the ED, overweight children were significantly more likely to be admitted to the hospital and to the ICU (Table 3).
To identify significant predictors of hospitalization, a logistic regression was performed with hospital admission as the dependent variable and overweight, age, gender, poverty status, and race/ethnicity as independent variables. MPIS was not included because of the relatively high incidence of missing data. After adjustment for the other covariates, overweight children were significantly more likely to be admitted than nonoverweight children (OR: 1.76; 95% CI: 1.23–2.51; P = .002). Race/ethnicity was also significant. Black (OR: 0.62; 95% CI: 0.40–0.95; P = .03) and Hispanic children (OR: 0.52; 95% CI: 0.35–0.78; P = .001) were less likely to be admitted than white children. Age (OR: 0.99; 95% CI: 0.95–1.02; P = .42), male gender (OR: 1.09; 95% CI: 0.80–1.49; P = .6), and poverty status (OR: 0.94; 95% CI: 0.65–1.36; P = .73) were not associated with admission in this analysis.
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DISCUSSION |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Although the exact relationship between overweight and asthma is unclear, there is evidence that overweight is associated with the development of a more difficult-to-control asthma phenotype.16–19 Previous investigators have linked overweight to poor asthma control,16–19 increased asthma severity,19,20 and a lower asthma-related quality of life.18 In studies of adult patients with asthma,17,18,20 overweight patients had more frequent exacerbations,17 increased symptoms such as shortness of breath and wheezing,18 and more difficult-to-control asthma.17,18 In children with asthma, overweight has also been linked to increased baseline symptoms,16,19 increased medication use,16,19 and increased health service use.16
In this study, we found that overweight was significantly associated with hospital and ICU admission for acute asthma exacerbations. Overweight children with asthma were significantly more likely to be admitted to the hospital and to the ICU than nonoverweight children, despite similar treatments received and similar illness severity on presentation. This is the first study in children to examine the relationship between overweight and hospital admission for asthma. In a previous study of children who were admitted to the ICU with asthma, we noted that overweight children who were admitted to the ICU with a severe asthma exacerbation had a significantly longer ICU length of stay and duration of hospitalization than nonoverweight children.21 This association persisted even after adjustment for baseline asthma severity and admission severity of illness. Taken together, these studies suggest that childhood overweight has significant adverse implications for children with asthma.
There are several potential mechanisms for the observed association of overweight and increased hospitalization for asthma. Overweight children may have previously undiagnosed concomitant medical problems related to overweight, such as upper airway obstruction, obesity hypoventilation syndrome, or gastroesophageal reflux.22 Although such conditions might have contributed to a more severe exacerbation and greater frequency of hospital admission, their incidence cannot be assessed in this retrospective trial because we cannot determine whether relevant history was obtained. Another potential mechanism is related to lung mechanics. Overweight children may have increased ventilation/perfusion mismatching as a result of atelectasis, possibly from reduced respiratory excursions from their increased body habitus and resultant decreased chest wall compliance.22
Finally, overweight per se may contribute to a more severe asthma phenotype.16,20 Overweight has been linked to a proinflammatory state that has been hypothesized to contribute to the development and worsening of asthma.22 Potential pathophysiologic mechanisms include an alteration in lung development and an alteration in inflammatory response that leads to an altered airway structure and an increased hyperresponsiveness.22 Continued research is needed to elucidate the underlying pathophysiology behind this potential association.
There may also be nonphysiologic mechanisms that contribute to the association between overweight and hospital admission. In this cohort, overweight children were more likely to live in an impoverished area than nonoverweight children. These children may have limited access to health care and increased exposure to aeroallergens that could affect their asthma control. Behavioral mechanisms may also play a role. Although outside the scope of this retrospective trial, it is possible that these overweight children have difficulties with self-regulation. This may translate into poor management of asthma through poor monitoring of symptoms, poor compliance with daily controller therapy, or lack of avoidance of triggers.
Some have suggested that overweight does not affect the severity of acute exacerbations. In a study by Thomson et al,23 572 adults with asthma were assessed on arrival to the ED with an acute exacerbation. In this population, 74% of the patients were overweight or obese, a significantly greater prevalence than the general population. Women had a significantly higher BMI than men in this population (32 ± 9 vs 28 ± 6; P < .001). Overweight patients with asthma did not differ in their response to therapy (assessed by change in peak expiratory flow) and were not more likely to be admitted to the hospital.
There are several possible explanations for the differences between the results of the Thomson et al study and those of ours. In the study by Thomson et al,23 hospital admission was not powered as the primary outcome measure, which may have accounted for the failure to find differences in admission rates. Different measures of overweight (BMI versus weight-for-age percentiles) were used, which may have also affected the results. In addition, the admission criteria in the multicenter trial by Thomson et al were not standardized, and this may have had an impact on the results. The prevalence of overweight also significantly differed. In the study by Thomson et al, the prevalence of overweight was significantly higher in patients with asthma than in the general population and in the population in our trial.23 Finally, in our study, pediatric patients with asthma may also have less overweight-related sequelae than adult patients, who may have had a longer duration of overweight.
There were significant differences in the racial/ethnic composition of the groups in our study. The overweight population had a lower proportion of white children and a higher proportion of black children. This supports previous studies in which the prevalence of overweight and the prevalence of asthma have been shown to differ by racial/ethnic groups.1,5
There were also significant differences in the race/ethnicity of the patients by disposition. Compared with white children, black and Hispanic children were less likely to be admitted to the hospital in this study. These findings were surprising. Other investigators have not found white patients to be admitted more frequently.24,25 Our findings should be interpreted with caution. This study was not designed to investigate racial/ethnic differences, and the data used were obtained indirectly from a hospital database and not directly from the patient. Determining the effects of race/ethnicity on overweight, asthma, and subsequent hospitalization for asthma is beyond the scope of our study and will require large clinical trials.
Our study is limited by several factors. In this retrospective trial, we were unable to use BMI to quantify overweight because of the lack of recorded height data. It is possible that children of above- or below-average heights could have skewed the results. A prospective trial would eliminate the limitations of a chart review and allow for a more rigorous definition of overweight. However, weight-for-age percentiles are the most commonly used indicator by pediatricians to assess the size and growth patterns of individual children in the United States26,27 and have been used to assess overweight in similar studies.21 In addition, a clinical asthma score was not assessed at the time of presentation for all children. However, similar proportions of children in the overweight and nonoverweight groups had documented severity of illness scores, suggesting that the lack of this information was not a factor in the results of this study.
This study included children as young as 2 years with physician-diagnosed asthma. Most pulmonologists do not diagnose asthma at this early age, preferring to wait until age 4 or 5 years to establish a pattern of chronicity. However, many children in this age group carry a diagnosis of asthma from their primary care provider and are treated as such. In this cohort, 298 of the 884 visits were in children who were younger than 5 years. When children who were younger than 5 years were eliminated, the results of this study did not change. Significantly more overweight children who were 5 years of age were hospitalized for an acute asthma exacerbation than nonoverweight children (33% vs 24%; P = .03). Inclusion of this younger population did not seem to affect significantly the results of this study.
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CONCLUSIONS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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In this cohort of all children who presented to an ED with an asthma exacerbation during a calendar year, overweight children with asthma were significantly more likely to be admitted to the hospital than nonoverweight children. Overweight is known to be associated with significant health-related consequences in children. This study identifies another important area in which overweight adversely affects the health of US children. Future studies should attempt to elucidate this link.
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ACKNOWLEDGMENTS |
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We thank the Office of Health Information Management at Connecticut Children's Medical Center and, particularly, Debra Brodacki-Magnan and Liz Taylor.
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FOOTNOTES |
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Accepted May 17, 2007.
Address correspondence to Christopher L. Carroll, MD, Division of Pediatric Critical Care, Connecticut Children's Medical Center, 282 Washington St, Hartford, CT 06106. E-mail: ccarrol{at}ccmckids.org
The authors have indicated they have no financial relationships relevant to this article to disclose.
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PEDIATRICS (ISSN 1098-4275). ©2007 by the American Academy of Pediatrics
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