Utilization due to chronic obstructive pulmonary disease and its predictors: a study using the U.S. National Emergency Department Sample (NEDS)

Chronic obstructive pulmonary disease (COPD) is associated with significant morbidity and health care costs worldwide [1]. COPD is the third leading cause of mortality in the U.S. and affects >12 million Americans [2, 3]. COPD was associated with $32 billion in costs in 2010 in the U.S. [4]. It frequently leads to inability to work and mobility limitations [5], which poses high societal economic burden [6]. COPD is associated with significant decrements in quality of life [7], worst in those with higher COPD disease severity [8, 9]. In addition to clinical burden, the inability to work due to COPD also poses high economic burden on both patients and governments [6].

Acute exacerbations of COPD are associated with significant morbidity, and decrements in quality of life [10, 11] and lead to frequent ED visits and hospitalizations. Studies have examined factors associated with hospitalization in patients with COPD, mostly in single-center settings or small cohorts [12‐14]. One study using a nationally representative U.S. sample found that EDs with higher COPD volume had lower mortality and shorter hospital length of stay [15] compared to those with a lower volume. A previous study using the U.S. National Hospital Ambulatory Medical Care Survey (NHAMCS) from 1993 to 2005 reported 0.6 million COPD visits annually [16], consistent with the estimates reported earlier using the National emergency Department (NEDS) data [15].

Previous studies of COPD ED visits focused on time-trends in visits [17], effect of hospital volume on mortality [15] and trends in treatment [16]. Few, if any data, are available regarding outcomes after an ED visit for COPD. A recent NEDS study comparing COPD with other chronic conditions combined COPD and bronchiectasis and did not provide separate data for COPD [17]. An older study estimated 1.5 million emergency department visits in 2002 in the U.S. [18]. These Centers for Disease Control and Prevention (CDC) data are 15-years old. Thus, contemporary data related to ED and inpatient burden due to COPD in the U.S. are needed, to better understand the current COPD burden on the healthcare system. Our objective was to examine the predictors and estimates of ED and inpatient utilization due to COPD as the primary diagnosis and post-hospitalization disposition, using contemporary NEDS data.

In this study using the NEDS, a U.S. representative national sample, we studied utilization of ED and inpatient resources with COPD as the primary diagnosis. We found that COPD was associated with >1 million ED visits and over half a million hospitalizations in 2012. Our estimates for the overall number of ED visits and inpatient hospitalizations related to COPD are similar to those reported in a study that combined COPD and bronchiectasis [17]. A previous study of trends in COPD treatment in the ED showed higher concordance with treatment recommendations in the recent years [16], indicating that quality of COPD care in the ED may be improving over time. We also examined factors associated with health resource utilization and charges for ED and inpatient visits due to COPD. Several findings merit further discussion.

First, we found that several sociodemographic, comorbidity, and hospital factors were associated with the risk of hospitalization among COPD patients who presented to ED with COPD as the primary diagnosis. Previous studies have focused on pulmonary function status and COPD medications as predictors of COPD hospitalization and associated costs [22, 23], but did not examine socio-demographic and hospital characteristics in detail. Our study examined these key characteristics and made important observations.

We found that older age, median household income above $48,000, metropolitan residence and the presence of comorbidities were each associated with higher risk of hospitalization. The association of older age with higher risk of COPD hospitalization is not surprising and confirms earlier similar findings from studies of smaller sample sizes [12, 24], now in a larger, representative U.S. sample. The association of higher median household income with a higher risk of COPD hospitalization/costs in interesting and extends a similar finding from other chronic conditions [25, 26] to COPD. Since models were adjusted for insurance type, the income effect is independent of insurance status and type. It is possible that income reflects education level or health literacy level, both of which might impact the risk of hospitalization. The association of female sex with higher odds of COPD hospitalization is consistent with a similar finding from Danish population-based study of 1.5-fold higher risk [27]. Medicaid or self-pay insurance status, hospital location in Midwest, South or Western U.S. were associated with lower risk of hospitalization after ED visit for COPD. The regional differences may be related to region-specific practices, differing severity of COPD and/or coexistent comorbidities by region, distance to nearest medical center etc. To our knowledge, our study is the one of the first U.S. studies to comprehensively examine the association of important socio-demographic, comorbidity and hospital characteristics and factors with COPD-hospitalization.

Comorbidities were risk factors for COPD hospitalizations. Diabetes, hypertension, heart failure, hyperlipidemia, and CHD were each associated with 1.2–2.3 fold higher odds of COPD hospitalization. Previous literature examining the association of comorbidities with COPD admission is somewhat contradictory. Coronary artery disease and diabetes mellitus were significant risk factors for COPD admission in some studies [28, 29], but other studies found no association of comorbidities with COPD readmission [30‐33]. Potential reasons for differences in findings of previous studies are differences in comorbidities adjusted in the analyses, study settings, and omission of important confounders in some studies. General interventions such as physical rehabilitation can improve outcomes of patients hospitalized with COPD [34]. Other specific interventions and management strategies targeting these comorbidities (diabetes, hypertension, HF, CHD etc.) in patients with COPD might reduce COPD-associated inpatient utilization.

We found that renal failure was associated with 3.1-times higher odds and osteoarthritis with 5.0-fold higher odds of hospitalization among COPD patients who presented to ED. To our knowledge, these findings are novel. Renal failure has been previously associated with higher mortality in hospitalized COPD patients, but risk of hospitalization was not assessed [35‐37]. Whether the increased hospitalization risk is due to the presence of renal failure or its worsening during the treatment of COPD exacerbation with corticosteroids and antibiotics in the ED, cannot be determined from our study. Similar to our observation of $4,756 unadjusted higher total charges in COPD patients with renal failure, a recent study by Manino et al. reported that the average all-cause total health-care costs from the index date to 360 days after the index date were highest for patients with chronic kidney disease, by $41,288 [38]. Therefore, future studies need to examine whether optimization of renal function by adequate hydration, medication management and optimization of renal function during a COPD flare and its treatment may help in reducing this risk of COPD hospitalization.

Osteoarthritis is associated with significant disability [39], loss of independence and higher health care utilization [40] in general. Difficulty in ambulation and daily activities due to concomitant osteoarthritis and associated frailty may contribute to a higher risk of hospitalization in COPD patients who also have difficulty in breathing. Use of assistive devices, exercises and self-management strategies reduce disability in osteoarthritis [41‐43]; newer methods such as neuromuscular electrical stimulation may be helpful in some patients [44, 45]. Future studies should examine if early diagnosis and optimal treatment of osteoarthritis in patients with COPD, focusing on inexpensive and commonly available non-surgical interventions for osteoarthritis, can reduce the risk of COPD hospitalization.

As noted above, our study findings of the association of various socio-demographic, comorbidity and hospital characteristics with COPD-hospitalization add to the current knowledge. Factors such as long term oxygen therapy, low health status, poor health related quality of life and inadequate physical activity [22] and body mass index, airflow obstruction, dyspnea, and exercise capacity (BODE) index [46] are associated with COPD hospitalization, and can predict hospital length of stay in and mortality in patients with COPD [47‐50]. Our study identified additional risk factors for COPD hospitalization. This new knowledge can help clinicians risk stratify COPD patients and target those with poorest prognosis.

Another finding was that older age, diabetes, HF and renal failure were associated with lower odds and male sex with higher odds of discharge to home (vs. nursing home/facilities) in hospitalized COPD patients. These findings are not unexpected; however, we are unaware of any studies with a representative U.S. sample that have explored this aspect of COPD care. Thus, these findings are novel. It remains to be seen whether optimization of HF, renal failure, and diabetes in COPD patients who are admitted to the hospital can increase the proportion discharged to home vs. skilled facilities.

Study findings must be interpreted considering study limitations. These findings are likely only applicable to ED-associated hospitalizations, not all hospitalizations. Due to the nature of NEDS database that captures data at the encounter level, rather than patient level, we are unable to examine risk factors for COPD readmissions, which are of interest clinically and for healthcare policy. We believe that at least some COPD admissions are readmissions. NEDS database does not link the ED visit to inpatient admission to another hospital, and we would likely miss this relatively uncommon event, since linkages of ED to hospitalization are at a hospital level. This underestimation is possible, but it is likely to be an uncommon or rare event. NEDS does not provide disease severity variables to adjust in the analyses, which can lead to residual confounding. Generalizability of findings to other countries may not be possible, since health care settings differ. Detailed assessments of COPD medications and their associations with COPD-related utilization would have provided additional insights; however, these data were not available in NEDs and this was beyond the scope of this study.

Our study has several strengths. NEDS is the largest, publically available U.S. sample of ED visits, therefore the findings are representative of and applicable to the U.S. population. We adjusted for several covariates and confounders including patient and hospital characteristics in patients with COPD to obtain unbiased estimates.

In conclusion, in this study of 2009-2012 NEDS data of patients presenting to the ED with COPD as the primary diagnosis, we studied patient discharge disposition from the ED and ED costs and for those admitted to the hospital, length of hospital stay, discharge disposition and costs. We found that older age, metropolitan residence and comorbidities (diabetes, HF, CHD, renal failure and osteoarthritis) were associated with higher risk of hospitalization and lower odds of discharge to home. Higher income was also associated with higher risk of hospitalization. We also identified other patient characteristics associated with hospital charges. Studies in the future should examine whether interventions targeting these modifiable factors can improve COPD outcomes.