Association Between Length of Stay and Readmission for COPD

Among patients admitted for chronic obstructive pulmonary disease (COPD) at Veterans Affairs hospitals, hospital-level length of stay was not associated with 30-day readmission.
Published Online: August 23, 2017
Seppo T. Rinne, MD, PhD; Meredith C. Graves, PhD; Lori A. Bastian, MD; Peter K. Lindenauer, MD; Edwin S. Wong, PhD; Paul L. Hebert, PhD; and Chuan-Fen Liu, PhD
ABSTRACT

Objectives: Recent financial penalties for high risk-adjusted chronic obstructive pulmonary disease (COPD) readmissions are causing hospitals to search for ways to reduce COPD readmissions. Although some have advocated for increasing the length of stay (LOS) as a method to decrease readmissions, the association between LOS and readmission is unclear. Our primary objective was to examine the association between LOS and readmission among patients admitted for COPD.

Study Design: We conducted an observational study of 33,558 veterans admitted to 130 Veterans Affairs hospitals for COPD from October 1, 2008, to September 30, 2011. 

Methods: We used multivariable regression to separately examine the associations of patient and hospital LOS with 30-day all-cause readmission. 

Results: At the patient level, compared with short LOS (<3 days), a longer LOS was associated with increased risk for readmission. The adjusted odds ratio was 1.39 (95% confidence interval [CI], 1.18-1.63) for medium LOS (3-4 days) and 2.03 (95% CI, 1.72-2.40) for long LOS (>4 days). On the hospital level, there was no association between LOS and readmission. 

Conclusions: On a patient level, a longer LOS for COPD hospitalizations was associated with higher risk for readmission, which is likely confounded by the severity of the illness. On a hospital level, LOS was not associated with readmission. These findings imply that, independent of other transitional care practices, altering the hospital LOS may not influence the risk of readmission.

Am J Manag Care. 2017;23(8):e253-e258
Takeaway Points

In a nationwide study of patients admitted for chronic obstructive pulmonary disease (COPD) to Veterans Affairs hospitals, we examined the association between length of stay (LOS) and readmission on the patient level and the hospital level separately. 
  • Patient-level LOS was associated with increased risk of readmission, which was likely due to residual confounding of severity of illness. 
  • Hospital-level LOS was not associated with readmission, and there was no association between risk-adjusted readmission and LOS. 
  • These findings imply that a strategy of simply keeping patients in the hospital longer is not likely to be an effective approach for reducing the risk of readmissions.
With healthcare costs continuing to rise, health systems are searching for ways to improve value-based care. Recently, CMS included readmissions for chronic obstructive pulmonary disease (COPD) in the Hospital Readmission Reduction Program, in which hospitals with excessive risk-adjusted readmission rates are financially penalized.1 Some have argued that keeping patients in the hospital longer would allow more time for optimal medical management and reduce the risk for readmission.2 However, the relationship between length of stay (LOS) and readmission is still unclear, and it is unknown whether increasing LOS is associated with lower readmission rates.

COPD is one of the most common chronic diseases leading to hospitalization in the United States.3 There are more than 700,000 COPD hospitalizations in the United States each year, accounting for more than $6 billion in healthcare spending4,5; average LOS for patients admitted with COPD varies widely between hospital systems.6,7 Furthermore, clinical trials on COPD hospitalizations have shown that early hospital discharge with home healthcare can effectively reduce LOS as well as readmissions in select patients.8-10 These findings suggest that opportunities may exist to safely improve hospital efficiency by reducing LOS for COPD.

Observational studies examining the relationship between LOS and readmission are frequently confounded by the severity of the illness,11,12 which makes it difficult to study this association. Patients who are sicker tend to require longer LOS and have higher risk of readmission. Several studies have attempted to overcome these challenges by observing variations in readmission rates corresponding to temporal trends in LOS.13-15 However, these studies have been unable to account for other temporal trends in clinical practice that may impact the outcome. Randomized trials on LOS could provide additional evidence, but they would be methodologically challenging to design and conduct.

The primary objective of this study was to examine the association between LOS and all-cause 30-day hospital readmission among patients who were admitted to Veterans Affairs (VA) hospitals for COPD. We first examined how individual patient LOS was associated with patient-level readmission risk. To determine the impact of organizational influences on patient outcomes, we then assessed how median hospital LOS was associated with patient-level readmission risk. Lastly, we examined the relationship between hospital-level risk-adjusted readmission rates and risk-adjusted LOS.

METHODS

Study Design and Population

We performed an observational study of patients admitted to VA hospitals for COPD during the fiscal years 2009 to 2011 (October 1, 2008, to September 30, 2011). We only included veterans who had least 1 year of VA care prior to index hospitalization. We identified 38,128 unique patients with COPD admissions by a principal International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) discharge diagnosis of COPD (491.0, 491.1, 491.2, 491.8, 491.9, 492.0, 492.8, 493.2, and 496), which is a validated approach that has been used in other VA studies.16 We excluded hospitals that admitted fewer than 25 patients for COPD during the study period (n = 11) to ensure stability in hospital-level covariate measures and readmission rates. We also excluded patients who died during hospitalization (n = 518), were discharged to a nursing hospital (n = 683), were transferred to a non-VA hospital (n = 2773), had an LOS of less than 1 day (n = 502), or had an LOS longer than 30 days (n = 83). Patients who died within 30 days of hospital discharge represented a small fraction of the total sample (n = 710), and they were included in the analysis. Repeating the analysis after excluding these patients did not substantially change our findings. Data on readmissions were collected from VA administrative databases and Medicare claims. The VA Puget Sound and VA Connecticut Healthcare Systems institutional review boards approved the study.

LOS Measures

The 2 independent variables of interest were: 1) patient LOS and 2) hospital median LOS. Patient LOS was calculated as the difference between the calendar date of admission and discharge. Given the skewness of LOS, we classified patient-level LOS into short (<3 days), medium (3-4 days), and long (>4 days), based on tertiles. Hospital LOS was calculated as the median LOS for all patients with COPD admitted within each hospital and was analyzed separately to determine the impact of organizational variation in LOS. To avoid the assumption that the relationship between hospital LOS and readmission was linear, hospital LOS was also broken into 3 categories for analysis. Given that the majority of patients were admitted to a hospital that had a median LOS of 3 days, we examined the following categories: fewer than 3 days, 3 days, and more than 3 days.

Readmission Measures 

The primary outcome of interest was hospital readmission for any cause within 30 days of discharge from index hospitalization. This outcome is consistent with the focus of the Hospital Readmissions Reduction Program (HRRP) on improving diverse readmissions. For each patient, only the first readmission within 30 days after index hospitalization was included in the analysis. Readmission data was collected from VA electronic health records and Medicare claims.

Covariates

We controlled for baseline patient characteristics including age, gender, race, marital status, distance to index hospital, Medicare and Medicaid status, co-payment status, number of home zip codes in the year prior to index hospitalization (1 vs >1), and discharge against medical advice in the prior year. To measure severity of illness, we included more than 30 diseases using inpatient and outpatient ICD-9-CM codes from the year prior to index hospitalization based on a previously validated risk score.17 The comorbidities included multiple conditions that frequently affect patients with COPD, such as heart disease, pulmonary vascular disease, and cancer. Each comorbidity was included in the model separately, and we also included an overall measure of comorbidity burden prior to index hospitalization using the Hierarchical Condition Category (HCC).18

The number of VA hospitalizations and clinic visits in the prior year were divided into quartiles and included as covariates in the analyses. Information on baseline COPD therapy included number of short-acting beta-agonist (SABA) canisters dispensed and prescriptions (yes/no) for nebulized SABAs, ipratropium, tiotropium, long-acting beta-agonists (LABAs), inhaled corticosteroids, and oral steroids in the year prior to index hospitalization. We did not have information on combined LABAs and inhaled corticosteroid medications. We also included information on whether patients were started on new invasive or noninvasive mechanical ventilation during index hospitalization as a proxy for severity of illness. Finally, to account for differences in LOS and readmission rates over time, we included the fixed effects of the fiscal year of patient discharge in the analyses.

Analysis

We conducted unadjusted analyses, including χ2 tests and t tests, to examine the association between LOS and readmission at the patient level and hospital level. We then estimated separate mixed effects multivariable logistic regression models to examine: 1) patient-level LOS and 2) hospital-level LOS. We calculated all-cause risk-adjusted readmission rates for each hospital using multivariable logistic regression and calculated risk-adjusted LOS using multivariable negative binomial regression. For both risk-adjusted models, we controlled for patient characteristics, included fixed effects for the hospital, and clustered at the hospital level. Risk-adjusted rates were predicted for each hospital, with patient characteristics held constant at national mean levels. We graphed the hospital-level risk-adjusted readmission rate and risk-adjusted LOS against each other and calculated Pearson’s correlation coefficient. 

In a sensitivity analysis, we repeated our regression analyses to examine the association between LOS and all-cause 30-day readmission among the frailest populations in our cohort, including: 1) patients older than 75 years and 2) patients who had the most comorbidities based on the highest HCC quartile. We also repeated our analysis using COPD-specific 30-day readmissions.

RESULTS

We included 33,558 patients who were admitted for COPD at 130 hospitals in our analyses. The mean patient LOS was 3.99 days (standard deviation [SD] = 4.06). There was notable skewness in patient LOS (Figure 1). Dividing patient LOS into tertiles yielded 13,194 patients who had an LOS shorter than 3 days; 10,760 patients who had an LOS of 3 to 4 days; and 9604 patients who had an LOS longer than 4 days. There was less skewness in median hospital LOS (Figure 2). Dividing hospital LOS into 3 categories yielded 6414 patients at 25 hospitals with a median LOS shorter than 3 days; 20,506 patients at 70 hospitals with a median LOS of 3 days; and 6638 patients at 35 hospitals with a median LOS longer than 3 days.

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