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Original Research: Asthma |

Rates and Correlates of Relapse Following ED Discharge for Acute AsthmaAsthma Relapses: A Canadian 20-Site Prospective Cohort Study FREE TO VIEW

Brian H. Rowe, MD, FCCP; Cristina Villa-Roel, MD; Sumit R. Majumdar, MD, MPH; Riyad B. Abu-Laban, MD, MHSc; Shawn D. Aaron, MD; Ian G. Stiell, MD; Jeffrey Johnson, PhD; Ambikaipakan Senthilselvan, PhD; for the AIR Investigators
Author and Funding Information

From the Department of Emergency Medicine (Drs Rowe and Villa-Roel), the Department of Medicine (Dr Majumdar), and the School of Public Health (Drs Rowe, Villa-Roel, Johnson, and Senthilselvan), University of Alberta, Edmonton, AB; the Department of Emergency Medicine (Dr Abu-Laban), University of British Columbia, Vancouver, BC; and the Department of Medicine (Dr Aaron) and the Department of Emergency Medicine (Dr Stiell), The Ottawa Hospital Research Institute, University of Ottawa, Ottawa, ON.

CORRESPONDENCE TO: Brian H. Rowe, MD, FCCP, Department of Emergency Medicine, University of Alberta, 1G1.43 Walter C. Mackenzie Health Sciences Center, 8440-112 St, Edmonton, AB T6G 2B7, Canada; e-mail: brian.rowe@ualberta.ca


FUNDING/SUPPORT: This study was supported by the Canadian Institutes of Health Research (CIHR), Ottawa, Ontario, and the Medical Services Incorporated Foundation (MSI), Edmonton, Alberta.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2015;147(1):140-149. doi:10.1378/chest.14-0843
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BACKGROUND:  Acute asthma is a common ED presentation. In a prospective, multicenter cohort study, we determined the frequency and factors associated with asthma relapse following discharge from the ED.

METHODS:  Adults aged 18 to 55 years who were treated for acute asthma and discharged from 20 Canadian EDs underwent a structured ED interview and a follow-up telephone interview 4 weeks later. Standardized antiinflammatory treatment was offered at discharge. Multivariable analyses were performed.

RESULTS:  Of 807 enrolled patients, 58% were women, and the median age was 30 years. Relapse occurred in 144 patients (18%) within 4 weeks of ED discharge. Factors independently associated with relapse occurrence were female sex (women, 22% vs men, 12%; adjusted OR [aOR], 1.9; 95% CI, 1.2-3.0); symptom duration of ≥ 24 h prior to ED visit (long duration, 19% vs short duration, 13%; aOR, 1.7; 95% CI, 1.3-2.3); ever using oral corticosteroids (ever use, 21% vs never use, 12%; aOR, 1.5; 95% CI, 1.1- 2.0); current use of an inhaled corticosteroid ([ICS]/long-acting β-agonist combination product (combination product, 25% vs ICS monotherapy,15%; aOR, 1.9; 95% CI, 1.1-3.2); and owning a spacer device (owning one, 24% vs not owning one, 15%; aOR, 1.6; 95% CI, 1.3-1.9).

CONCLUSIONS:  Despite receiving guideline-concordant antiinflammatory treatments at ED discharge, almost one in five patients relapsed within 4 weeks. Female sex, prolonged symptoms, treatment-related factors, and markers of prior asthma severity were significantly associated with relapse. These results may help physicians target more aggressive interventions for patients at high risk of relapse.

Figures in this Article

Asthma is a serious chronic lung disease that affects between 7% and 10% of the adult population; in 2012, approximately 2.4 million Canadians aged 12 years and older (8.1%) reported being given a diagnosis of asthma by a health professional.1,2 It is estimated that nearly 2 million ED asthma visits occur annually in the United States alone,3 and 80% to 90% of the patients with acute asthma who present to the ED will be discharged.4 Clinical studies indicate that between 5% and 25% of patients discharged from the ED will relapse within the first week, and 21% to 35% will relapse within 3 weeks.5,6

Asthma relapses represent important adverse health outcomes for the patient and result in significant costs to the health-care system.7,8 A variety of demographic, historical, and treatment factors have been associated with relapse after ED discharge for acute asthma, but previous studies have been limited because they did not account for disease severity at presentation, were not performed in a setting of universal health-care access,911 failed to standardize treatment after discharge, and/or involved patients with other comorbidities or COPD.9,10 In an effort to enhance the interpretation and translation of research findings into practice, we undertook a prospective, multicenter cohort study to document relapse events and factors associated with relapse in the month following discharge from Canadian EDs for patients with acute asthma prescribed evidence-based antiinflammatory treatments.

Study Design and Setting

This prospective cohort study enrolled patients treated for acute asthma in 20 EDs across Canada between November 2003 and March 2007. The study sites were all members of the Canadian Association of Emergency Physicians Research Consortium. Sixteen of the EDs were urban teaching sites, and four were community-based EDs. The median ED census of the study sites was 50,000 patients per year. Institutional research ethics board approval was obtained from each site, and written informed consent was obtained from all participants.

Study Population

All patients aged 18 to 55 years presenting with acute asthma were eligible. Asthma diagnosis was made by the treating emergency physician using clinical criteria (eg, history, response to β-agonists, and symptoms of shortness of breath, wheezing, cough, or chest tightness). For pragmatic purposes, we included all patients with these criteria with a history of < 30 pack-years of smoking. Patients with exacerbations of COPD, mild obstruction (> 80% predicted peak expiratory flow [PEF] at presentation), chronic (daily) use of or contraindications to oral corticosteroids (OCSs), and serious or unstable comorbidities were excluded. Subjects with pneumonia, requiring admission, who were clinically unstable, or who had documented pregnancy were not enrolled. Inability to communicate in English and to provide informed consent, cognitive impairment, and refusal to take OCSs were additional exclusion criteria. Refusals, missed patients, and other reasons for nonenrollment were documented.

Antiinflammatory Treatment

ED management was left to the discretion of the treating emergency physician; however, this usually included inhaled β-agonists, short-acting anticholinergics, and a systemic corticosteroid. At discharge, emergency physicians prescribed medications as deemed appropriate and provided patients with a personalized discharge plan regarding medication use, follow-up, and criteria for return for reassessment in the event of symptom worsening. A short course of prednisone (50 mg daily for 5-7 days) was provided by the study nurse; physicians were also strongly advised to maintain any inhaled corticosteroid (ICS) or ICS/long-acting β-agonist (LABA) treatment or to add an ICS to patients not already taking one.

Baseline Data Collection

In a structured interview, we collected sociodemographic data, including age, sex, race (by visual assessment), marital status, level of education and employment, and availability of primary care provider. Asthma history, use of preventive actions, and medications were ascertained by patient recall while they were in the ED. Smoking status was coded as never, previous, or current smoker. Insurance status related to medication coverage, percentage of medication costs usually paid by patients, and any self-reported reduction in medication use in the previous 12 months were recorded.

Information on ED course, management, and discharge plan were obtained through medical record review following standard guidelines that include the need for explicit criteria and interrater reliability assessment. Severity at presentation was assessed through the Canadian Triage and Acuity Scale, which is the national standard for Canadian ED patients and has been shown to be valid and reliable.12 PEF was performed before or after the first ED treatment and was standardized as the percentage of the patient’s predicted value according to age, sex, race, and height13; spirometry was performed before discharge.

Study Outcomes

Relapse was defined as an unscheduled visit to any ED, clinic, or physician office for worsening asthma (eg, cough, dyspnea)9,14 and was assessed by telephone at 3 days, 2 weeks, and 4 weeks after discharge. For any relapses identified at follow-up, objective confirmation was sought from the medical records. All relapses were adjudicated by an external review committee without knowledge of the patients or the treatments received.

Other Measurements

Typical ICS side effects (eg, insomnia, hoarseness, swelling, sore throat, and nausea) were collected at time of follow-up. Scheduled follow-up visits to a primary care provider or clinic were documented with the exception of routine asthma checkups, which were not considered relapses. Adherence to the post-ED short course of OCSs was assessed at the 3-day and 2-week follow-up phone calls by asking whether the patient had taken the prednisone pills as prescribed and instructed. The use of ICSs (monotherapy or in combination with LABA agents) was also assessed.

Statistical Analysis

Descriptive data included numbers and proportions or medians with interquartile range (25th and 75th percentiles) as appropriate. The agreement between the two relapse adjudicators was measured using the κ statistic. Baseline comparisons based on relapse status 4 weeks after discharge were performed using generalized estimating equations to adjust for the clustering of patients within the study sites. Multiple logistic regression analyses with generalized estimating equations were performed, and we used purposeful variable selection methods. First, variables identified at P < .10 significance in the univariate comparison and those deemed to be of clinical importance (eg, age and sex) were selected. A final model was obtained after assessing the confounding effects of variables that could be removed (≥ 15% change in the study estimates between the models including/not including them) and categorizing those variables that did not fulfill the assumption of linearity (age and ED length of stay). Adjusted OR (aORs) and 95% CIs for the variables included in the final multiple logistic regression are reported in the results. No statistically significant (P < .05) first-order interaction terms were found, and none were included in final models. All analyses were performed using StataCorp 2009 Stata Statistical Software: Release 11 (StataCorp LP).

Patients

Over the study period, 4,598 ED patients were screened for enrollment, and 3,248 (71%) were potentially eligible (Fig 1). Of these, 2,441 patients were ineligible because of one or more exclusion criteria, and 807 were enrolled in the cohort.

Figure Jump LinkFigure 1 –  Study patient flow. *Exclusions included not being treated in the ED for acute asthma (21%), admissions (16%), unclear clinical diagnosis of asthma (9%), refusal to follow-up (7%), and suspected pneumonia (6%). Other reasons for exclusions (41%) were age outside the study range, > 80% peak expiratory flow at presentation, antibiotic treatment of pneumonia, previous participation in the study, chronic use of oral corticosteroids, COPD exacerbation or ≥ 30 pack-y of smoking, pregnancy, cognitive impairment, severe comorbidities, refusal to take oral prednisone, and need of immediate resuscitation.Grahic Jump Location
Patient Characteristics

Overall, 57% of the patients were women, the median age was 30 years (interquartile range, 23-39 years), and most (85%) were white. Tables 1 and 2 present sociodemographic and clinical data, ED treatments, and asthma severity stratified by asthma relapse within 4 weeks. In general, other than sex and symptom duration, most correlates of relapse were related to the intensity of asthma management. Based on initial assessments using various criteria, most patients were classified as having severe acute asthma.

Table Graphic Jump Location
TABLE 1 ]  Characteristics of Patients With Acute Asthma Discharged From ED Categorized by Relapse Status

Data are presented as No. (%) or median (interquartile range presented as 25th and 75th percentiles). OR, 95% CI, and P values are adjusted estimates from generalized estimating equation. ICS = inhaled corticosteroid; LABA = long-acting β-agonist; SABA = inhaled short-acting β-agonist.

Table Graphic Jump Location
TABLE 2 ]  Acute Asthma Presentation and ED Course Categorized by Relapse Status

Data are presented as No. (%), mean ± SD, or median (interquartile range presented as 25th and 75th percentiles). OR, 95% CI, and P values are adjusted estimates from generalized estimating equation. CTAS = Canadian Triage and Acuity Scale; EP = emergency physician; LOS = length of stay; MgSo4 = magnesium sulfate; PEF = peak expiratory flow; Sao2 = oxygen saturation. See Table 1 legend for expansion of other abbreviations.

Prior to the initial ED visit, 25% of patients were steroid naive, 29% were receiving ICS monotherapy, and 46% were receiving ICS/LABA agents (Fig 2, Table 1). Treatment of both groups was similar in the ED (Table 2). Treatment at discharge did vary slightly. For example, most patients (50%) were instructed to continue on their preexisting antiinflammatory drug, and 38% were prescribed a new ICS; however, 11% were not prescribed ICS agents at discharge (Fig 3, Table 2).

Figure Jump LinkFigure 2 –  Medication at ED presentation. ICS = inhaled corticosteroid; ICS + LABA = combination therapy; LABA = inhaled long-acting β-agonist; LEUK = leukotriene modifier/antagonist; OCS = oral corticosteroid; SABA = inhaled short-acting β-agonist. *Statistical significance (P < .05).Grahic Jump Location
Figure Jump LinkFigure 3 –  Medication at presentation and discharge. See Figure 2 legend for expansion of abbreviations.Grahic Jump Location
Patient Relapse

The two reviewers demonstrated high agreement relapse adjudication (κ = 0.97). Follow-ups at 3 days (89%), 2 weeks (82%), and 1 month (80%) after ED discharge were high. Those patients who were and were not followed up at 1 month had similar sociodemographic profiles (eg, age, sex, marital status, and education), asthma history, and indicators of severity at presentation (data not shown).

Early relapse (≤ 7 days) occurred in 86 patients (11%), relapse within 2 weeks occurred in 112 patients (14%), and relapse within 4 weeks occurred in 144 patients (18%) (cumulative data). Of all the patients who relapsed within 4 weeks of the ED visit, 130 (90%) relapsed once, 13 (9%) relapsed twice, and one (< 1%) relapsed three times during the follow-up period. Female patients relapsed more often and sooner than did male patients (P = .003) (Fig 4). Self-reported adherence to a short course of OCSs prescribed at discharge was high at day 3 (98%) and at completion of treatment follow-ups (95%). Most of the patients who relapsed (79%) sought ED care during the 4-week follow-up period, resulting in 18 hospitalizations (16% of all relapses; 2% of sample). One death (unrelated to asthma) occurred in the group of patients who did not relapse.

Figure Jump LinkFigure 4 –  Relapse timing based on patient sex.Grahic Jump Location
Factors Independently Associated With Relapse

Multivariable analyses indicated that the following factors were independently associated with relapse: female sex (22% [102 of 465] vs 12% male [42 of 342]; aOR, 1.9; 95% CI, 1.2-3.0), ≥ 24 h of symptoms prior to the ED visit (19% [116 of 595] vs 13% [26 of 201] short duration; aOR, 1.7; 95% CI, 1.3=2.3), ever receiving OCSs for asthma (21% [107 of 508] vs 12% [37 of 299] for never use; aOR, 1.5; 95% CI, 1.1-2.0), use of ICS/LABA combination agents (with or without extra ICSs) at the time of ED presentation (25% [66 of 263] vs 15% [42 of 285] ICS monotherapy; aOR, 1.9; 95% CI, 1.1-3.2), and owning a spacer device (24% [65 of 272] vs 15% [79 of 535] not owning one; aOR, 1.6; 95% CI, 1.3-1.9) (Table 3).

This multicenter prospective study examined the factors associated with relapse for patients with moderate to severe asthma exacerbations discharged from Canadian EDs following treatment with standard and evidence-based antiinflammatory care for acute asthma. This target population not only represents the majority of the patients with asthma seen in the ED, but also includes a significant number of patients who will revisit the ED within the next 3 weeks. Most importantly, even with reasonably guideline-concordant discharge management, we observed that almost one in five patients experienced a relapse within 4 weeks of the ED visit. These results are consistent with a previous prospective study in which antiinflammatory treatments offered at discharge were not standardized,9 suggesting that both treatment and nontreatment factors contribute to relapse.

The following factors were independently and significantly associated with relapse: female sex, prolonged exacerbation of symptoms prior to the ED visit, ever receiving OCSs for asthma, use of ICS/LABA combination agents at the time of ED presentation, and owning spacer devices. Other studies have explored the factors associated with relapse in asthma; however, they used a shorter follow-up, did not provide all patients with OCSs, and had a lower proportion of patients discharged on recommended preventer inhaled medications.9,10

Despite efforts to maximize evidence-based medical treatment at discharge, the proportion of study patients who received maximal medical care following discharge was lower than desired. For example, although approximately 98% received OCSs for 5 to 7 days as recommended,15 11% still received no ICS agents.6 Nonetheless, these treatment approaches are far more aggressive than those used in other studies that evaluated the factors associated with asthma relapse.16 Because this study arguably provides the highest proportion of evidence-based antiinflammatory treatments outside clinical trials, it is appropriate to focus on the nonmedication management issues associated with relapse after discharge.

Women were far more likely to relapse than were men (Fig 4). Our results are consistent with findings from other studies indicating that women with asthma experience more severe symptoms, which may result in more frequent relapses.17 Moreover, it has been suggested that women have a phenotype of asthma that is more resistant to ICS agents.18 Although future mechanistic research will likely contribute to our understanding of these differences, women discharged from the ED should be considered to be at a higher risk of relapse.

Having prolonged symptoms prior to the ED visit was associated with a higher risk of relapse, and this is consistent with previous findings.9 Our results also suggest that patients who report ever having received OCSs for asthma and those using an ICS/LABA combination agent at presentation were more likely to experience a relapse. These observations may reflect past poor control and current severe disease status, respectively. Demonstration of an association does not prove causation. It is likely that the use of these medications is confounded by severity; sicker patients with more severe chronic asthma are treated with more aggressive therapy.

Finally, a failure to identify associations between relapse and several widely cited factors was important.911 Most notably, the role of pulmonary flow measures has been a controversial area in the literature.1922 It appears that once the physician decides on patient discharge, the patient’s change in PEF (δ between pre- and posttreatment measures) or the % predicted FEV1 at discharge from the ED were not helpful in predicting future relapse.

Limitations

Some important limitations must be considered when interpreting our results. First, our sample was restricted to a specific group of patients with asthma recruited in mostly academic centers and during variable research coverage hours (maximum coverage of 8:00 am to 12:00 am Monday to Friday; 10:00 am to 6:00 pm Saturday and Sunday); these findings may not be representative of all patients with asthma presenting to Canadian EDs, nor generalizable to those discharged from EDs after presenting with an extremely severe asthma-related condition with mild disease, pneumonia, and mixed entities (including, for example, COPD exacerbations). Second, despite the fact that we used a common definition of asthma in ED settings, some may feel this is a less valid approach than using a specific set of international criteria.23 We selected this approach because it has been used elsewhere, is clinically sensible, and is valid within the ED setting.2426 Third, although patients may have been more inclined to respond to the research staff questions because of their acute condition, most of the information collected in the ED would not have changed if asked during a different time frame. Information on asthma history, prevention actions, and medications could have been assessed more accurately; however, the risk of misclassification is minimal because the information collected through this ED interview did not influence the definition of the primary study outcome. Fourth, the definition of relapse did not include telephone contact with physicians for medication adjustment; because this practice is rare in Canada, this approach is unlikely to influence our results. Furthermore, we collected objective evidence of worsening asthma and adjudicated outcomes by an external committee to minimize bias. Fifth, initial PEF and FEV1, as well as % predicted PEF and FEV1 measurements, were not obtained on all patients, which could have influenced our results. On the other hand, we elected to reflect the real ED practice (which underuses pulmonary function measures), include a more generalizable sample, and ensure a high proportion of patients with discharge pulmonary function measures. Sixth, self-reported nonadherence to OCSs was extremely low in the entire cohort; therefore, nonadherence could not be examined as a relapse factor. Adherence to the completion of the treatment prescribed in the ED was measured only through self-report because this study did not include an in-person assessment after the ED visit; inhaler techniques were not assessed for the same reason. Similarly, 89% of patients were prescribed an ICS at discharge, so our study did not have the power to determine the influence of ICS agents on relapse in the 4-week post-ED period. Seventh, the generalizability of the study results may be limited because all patients received OCSs and a high proportion received inhaled antiinflammatory agents; however, because these are evidence-based and recommended treatments, these results would reflect the best case scenario. Finally, our 4-week follow-up could be deemed by some to be insufficiently long for identifying all relapse events; however, this period has been used in similar studies and randomized controlled trials.15,21 Moreover, longer observation can be biased by reexposure to other asthma precipitants, and thus may be a reflection of a new exacerbation rather than a relapse event.

This study identified a practical set of factors that could be used by physicians to identify patients at risk of relapse after discharge from an ED and guide health providers in the development of evidence-based clinical decision rules, educational strategies, and optimal follow-up plans for the prevention of relapses. We found that female sex, prolonged exacerbation symptoms prior to the ED visit, and some markers of asthma treatment intensity prior to the ED visit were significantly associated with relapse. Although some further work is required to validate our specific findings, we believe that the presence of one or more of these risk factors identifies patients at high risk of relapse who may benefit from more intensive ED management, disposition decisions (eg, early admissions), and discharge plans (eg, closer follow-up by a primary care provider or specialist after discharge).

Author contributions: B. H. R. is guarantor of the study. B. H. R., C. V.-R., S. R. M., R. B. A.-L., S. D. A., I. G. S., J. J., and A. S. contributed to the design and execution of the study and the drafting and revision of the manuscript.

Financial/nonfinancial disclosures: The authors have reported to CHEST the following conflicts of interest: Within the past 3 years, Dr Rowe has received research funding from the following respiratory companies: GlaxoSmithKline and ElectroCore Medical, LLC. Drs Villa-Roel, Majumdar, Abu-Laban, Aaron, Stiell, Johnson, and Senthilselvan have reported that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Role of sponsors: The sponsors had no role in the design of the study, the collection and analysis of the data, or the preparation of the manuscript.

Collaborators: Duncan S. Mackey, MD; Alan Walker, MD; Scott Ross, MD; Bryan Young, MD; Sam G. Campbell; Marco L. Sivilotti, MD; Bjug Borgundvaag, MD, PhD; Christopher J. Boule, MD; Robert Stenstrom, MD, PhD; Andrew Worster, MD; Shaun Visser, MD; Eddy Lang, MD; Marc Afilalo, MD; John Froh, MD; Marcel Emond, MD; Jacques S. Lee, MD; and Chantal Guimont, MD, PhD.

Other contributions: The authors thank the CIHR, Ottawa, ON, and the MSI, Edmonton, AB, who provided research funding for this study; and the Department of Emergency Medicine Research Group (EMeRG) at the University of Alberta for their in-kind support of this project. The research team thanks Sandra Blitz for her assistance during the study design; the Epidemiology Coordinating and Research Center (EPICORE), Edmonton, AB, for their support in data collection and coordination; and Diane Milette for her secretarial support. The authors also express their gratitude to the following research staff for their assistance in site coordination (in order of recruitment): Marlene Myles, Ginny Willis, Leslie Tyler, Debbie Boyko, Michelle Pachal, Cathy Clement, Renee Vineff, Agnieszka Grabowski-Comeau, Kathy Bowes, Michelle Loftus, Sharon Oliveros, Crystal-Anne Smith, Barbara Boychuck, Christina Brean, Sandra Stoger, Cristina Ciolofan, Jan Buchanan, Tricia Pearson, Cynthia Reich, Patricia Chabot, Shana Huntly, and Annie-Claude D’Anjou.

aOR

adjusted OR

ICS

inhaled corticosteroid

LABA

long-acting β-agonist

OCS

oral corticosteroid

PEF

peak expiratory flow

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Figures

Figure Jump LinkFigure 1 –  Study patient flow. *Exclusions included not being treated in the ED for acute asthma (21%), admissions (16%), unclear clinical diagnosis of asthma (9%), refusal to follow-up (7%), and suspected pneumonia (6%). Other reasons for exclusions (41%) were age outside the study range, > 80% peak expiratory flow at presentation, antibiotic treatment of pneumonia, previous participation in the study, chronic use of oral corticosteroids, COPD exacerbation or ≥ 30 pack-y of smoking, pregnancy, cognitive impairment, severe comorbidities, refusal to take oral prednisone, and need of immediate resuscitation.Grahic Jump Location
Figure Jump LinkFigure 2 –  Medication at ED presentation. ICS = inhaled corticosteroid; ICS + LABA = combination therapy; LABA = inhaled long-acting β-agonist; LEUK = leukotriene modifier/antagonist; OCS = oral corticosteroid; SABA = inhaled short-acting β-agonist. *Statistical significance (P < .05).Grahic Jump Location
Figure Jump LinkFigure 3 –  Medication at presentation and discharge. See Figure 2 legend for expansion of abbreviations.Grahic Jump Location
Figure Jump LinkFigure 4 –  Relapse timing based on patient sex.Grahic Jump Location

Tables

Table Graphic Jump Location
TABLE 1 ]  Characteristics of Patients With Acute Asthma Discharged From ED Categorized by Relapse Status

Data are presented as No. (%) or median (interquartile range presented as 25th and 75th percentiles). OR, 95% CI, and P values are adjusted estimates from generalized estimating equation. ICS = inhaled corticosteroid; LABA = long-acting β-agonist; SABA = inhaled short-acting β-agonist.

Table Graphic Jump Location
TABLE 2 ]  Acute Asthma Presentation and ED Course Categorized by Relapse Status

Data are presented as No. (%), mean ± SD, or median (interquartile range presented as 25th and 75th percentiles). OR, 95% CI, and P values are adjusted estimates from generalized estimating equation. CTAS = Canadian Triage and Acuity Scale; EP = emergency physician; LOS = length of stay; MgSo4 = magnesium sulfate; PEF = peak expiratory flow; Sao2 = oxygen saturation. See Table 1 legend for expansion of other abbreviations.

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