Association of Medicaid Expansion Under the Affordable Care Act With Outcomes and Access to Rehabilitation in Young Adult Trauma Patients | Adolescent Medicine | JAMA Surgery | JAMA Network
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Table 1.  Characteristics of Hospitalized Young Adult Trauma Patients by Time Across 11 Medicaid Expansion States
Characteristics of Hospitalized Young Adult Trauma Patients by Time Across 11 Medicaid Expansion States
Table 2.  Changes in Insurance Coverage and Outcomes Across 11 Medicaid Expansion Statesa
Changes in Insurance Coverage and Outcomes Across 11 Medicaid Expansion Statesa
Table 3.  Characteristics of Hospitalized Young Adult Trauma Patients by Time Period for 3 Medicaid Expansion States vs 3 Nonexpansion States
Characteristics of Hospitalized Young Adult Trauma Patients by Time Period for 3 Medicaid Expansion States vs 3 Nonexpansion States
Table 4.  Changes in Insurance Coverage and Outcomes in 3 Medicaid Expansion vs 3 Nonexpansion Statesa
Changes in Insurance Coverage and Outcomes in 3 Medicaid Expansion vs 3 Nonexpansion Statesa
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Sommers  BD, Gunja  MZ, Finegold  K, Musco  T.  Changes in self-reported insurance coverage, access to care, and health under the Affordable Care Act.  JAMA. 2015;314(4):366-374.PubMedGoogle ScholarCrossref
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Sommers  BD, Maylone  B, Blendon  RJ, Orav  EJ, Epstein  AM.  Three-year impacts of the Affordable Care Act: improved medical care and health among low-income adults.  Health Aff (Millwood). 2017;36(6):1119-1128.PubMedGoogle ScholarCrossref
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Joseph  B, Haider  AA, Azim  A,  et al.  The impact of patient protection and Affordable Care Act on trauma care: a step in the right direction.  J Trauma Acute Care Surg. 2016;81(3):427-434.PubMedGoogle ScholarCrossref
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Cheslik  TG, Bukkapatnam  C, Markert  RJ, Dabbs  CH, Ekeh  AP, McCarthy  MC.  Initial impact of the Affordable Care Act on an Ohio Level I trauma center.  J Trauma Acute Care Surg. 2016;80(6):1010-1014.PubMedGoogle ScholarCrossref
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Zogg  CK, Payró Chew  F, Scott  JW,  et al.  Implications of the Patient Protection and Affordable Care Act on insurance coverage and rehabilitation use among young adult trauma patients.  JAMA Surg. 2016;151(12):e163609.PubMedGoogle Scholar
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Blavin  F.  Association between the 2014 Medicaid Expansion and US hospital finances.  JAMA. 2016;316(14):1475-1483.PubMedGoogle ScholarCrossref
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Agency for Healthcare Research and Quality. Healthcare Cost and Utilization Project website. https://www.hcup-us.ahrq.gov/. Published April 1, 2018. Accessed January 10, 2017.
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Han  X, Nguyen  BT, Drope  J, Jemal  A.  Health-related outcomes among the poor: Medicaid expansion vs. non-expansion states.  PLoS One. 2015;10(12):e0144429.PubMedGoogle ScholarCrossref
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Decker  SL, Kenney  GM, Long  SK.  Characteristics of uninsured low-income adults in states expanding vs not expanding Medicaid.  JAMA Intern Med. 2014;174(6):988-989.PubMedGoogle ScholarCrossref
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Bell  TM, Zarzaur  BL.  Insurance status is a predictor of failure to rescue in trauma patients at both safety net and non-safety net hospitals.  J Trauma Acute Care Surg. 2013;75(4):728-733.PubMedGoogle ScholarCrossref
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Soberg  HL, Roise  O, Bautz-Holter  E, Finset  A.  Returning to work after severe multiple injuries: multidimensional functioning and the trajectory from injury to work at 5 years.  J Trauma. 2011;71(2):425-434.PubMedGoogle ScholarCrossref
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Akande  M, Minneci  PC, Deans  KJ, Xiang  H, Chisolm  DJ, Cooper  JN.  Effects of Medicaid expansion on disparities in trauma care and outcomes in young adults.  J Surg Res. 2018;228:42-53.Google ScholarCrossref
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    Original Investigation
    August 15, 2018

    Association of Medicaid Expansion Under the Affordable Care Act With Outcomes and Access to Rehabilitation in Young Adult Trauma Patients

    Author Affiliations
    • 1Department of Critical Care Medicine, Nationwide Children’s Hospital, Columbus, Ohio
    • 2Center for Surgical Outcomes Research and Center for Innovation in Pediatric Practice, The Research Institute at Nationwide Children’s Hospital, Columbus, Ohio
    • 3Department of Surgery, Nationwide Children’s Hospital, Columbus, Ohio
    • 4Center for Pediatric Trauma Research, The Research Institute at Nationwide Children’s Hospital, Columbus, Ohio
    JAMA Surg. 2018;153(8):e181630. doi:10.1001/jamasurg.2018.1630
    Key Points

    Question  Was Medicaid expansion under the Affordable Care Act in its first year of implementation associated with improvements in insurance coverage and outcomes among young adults hospitalized for traumatic injury?

    Findings  In this study, there was an 18.2% increase in Medicaid coverage and a 15.1% decrease in lack of insurance among trauma patients hospitalized across 11 Medicaid expansion states. There were no significant changes in in-hospital mortality or unplanned readmission rates, but discharge to rehabilitation increased 1.2%, a significant difference.

    Meaning  In this study of hospitalized young adult trauma patients, Medicaid expansion has improved insurance coverage and access to postinjury rehabilitation.

    Abstract

    Importance  Trauma is the leading cause of death and disability among young adults in the United States. Young adults are also the age group most likely to be uninsured. Implementation of Medicaid expansion through the Affordable Care Act (ACA) has increased insurance coverage, but its associations with trauma care and outcomes among young adults nationwide remain unknown. We examined whether Medicaid expansion, in its first year, was associated with changes in insurance coverage and improved outcomes in young adults hospitalized for traumatic injury.

    Objective  To assess the associations of ACA Medicaid expansion with insurance coverage, in-hospital mortality, failure to rescue, access to rehabilitation, and unplanned readmissions among hospitalized young adult trauma patients across many US states.

    Design, Setting, and Participants  We used the Healthcare Cost and Utilization Project State Inpatient Databases to examine changes in insurance coverage and risk adjusted outcomes among young adults (age 19 to 44 years) who were hospitalized for injuries before and after Medicaid expansion and open enrollment occurred (2012-2013 vs 2014) in 11 US states that expanded Medicaid through the ACA. We also performed difference-in-difference analyses to compare these changes between 3 expansion states and 3 non-expansion states within the same geographic region.

    Results  Of the 141 187 trauma patients hospitalized across 11 Medicaid expansion states, 43 871 (31.1%) were women, and the mean (SD) age was 31.4 (7.6) years. Medicaid expansion was associated with an increase in Medicaid coverage from 16 229 individuals (16.7%) to 15 358 individuals (34.9%) (difference: 18.2% [95% CI, 16.5%-20.0%]; P < .001), a decrease in lack of insurance from 27 016 individuals (27.8%) to 5589 individuals (12.7%) (difference: −15.1% [95% CI, −16.8% to −13.5%]; P < .001), and an increase in discharge to rehabilitation from 9220 individuals (11.4%) to 4736 individuals (12.6%) (difference: 1.16% [95% CI, 0.55%-1.77%]; P < .001). We found no significant reductions in in-hospital mortality, failure to rescue, or unplanned readmissions. Similar results were found when 3 of these states were compared with 3 geographically and demographically similar states that had not enacted Medicaid expansion.

    Conclusions and Relevance  The first year of implementation of Medicaid expansion and open enrollment across 11 selected US states was associated with significant increases in Medicaid coverage, reductions in uninsured rates, and increased access to postdischarge rehabilitation among young adults hospitalized for injury. However, this study found no significant reductions in in-hospital mortality, failure to rescue, or unplanned readmissions.

    Introduction

    Among young adults in the United States, trauma is the leading cause of death and disability, accounting for more than 80 000 deaths each year among adults aged 18 to 44 years.1 The societal financial impact of traumatic injury is noteworthy, with medical and work loss–related costs reaching $214 billion for fatal trauma and $457 billion for nonfatal trauma in 2013.2 Trauma disproportionately affects persons of low socioeconomic status, persons of racial/ethnic minority status, and uninsured individuals, and both the quality of trauma care and patient outcomes have been reported to be worse in these sociodemographic groups.3,4 For example, both in-hospital and long-term trauma-related mortality are higher among uninsured people.5-9 Among hospitalized young adult trauma patients, even after adjustment for demographics, comorbidities, and injury severity, uninsured individuals are more likely to die in the hospital and also less likely to receive rehabilitative care after serious injury.4,10,11

    Quiz Ref IDPrior to the Affordable Care Act (ACA), more than 30% of young adults lacked health insurance.12 The ACA required states to extend Medicaid eligibility in 2014 to all nondisabled adults with incomes less than or equal to 138% of the federal poverty level.13 However, a 2012 Supreme Court ruling made Medicaid expansion under the ACA optional for states, and therefore only 31 states plus the District of Columbia have expanded Medicaid coverage to low-income adults to date.14 Medicaid expansion under the ACA has been associated with increased insurance coverage, increased health care use, improved self-reported health, and decreased health care–associated financial burden among low-income adults.15,16 Several studies of individual trauma centers in Medicaid expansion states and 1 study examining the state of Maryland have reported large increases in Medicaid coverage and decreases in uninsurance rates among trauma patients.17-20 Furthermore, in Maryland, Medicaid expansion has been associated with increased access to rehabilitation and decreases in both in-hospital mortality and failure to rescue rates.20 Although greater access to rehabilitation is likely a direct outcome of increased insurance coverage, reductions in in-hospital mortality and failure to rescue rates could be mediated by several factors. Such factors may include patients’ improved preinjury health status because of increased primary and preventive health care use postexpansion or increased resources at hospitals that, prior to Medicaid expansion, provided a large amount of uncompensated care.15,16,21 Nevertheless, given the large variability across states in trauma systems, Medicaid programs, and population characteristics, it is unclear whether the findings in Maryland can be extrapolated to other states. The impact of Medicaid expansion under the ACA on posthospitalization outcomes is also unclear. However, one might suspect that improved preinjury health status and access to post–acute care after Medicaid expansion would also impact posthospitalization outcomes, such as the rate of unplanned readmissions. The aim of this study was to assess the association of Medicaid expansion under the ACA in its first year with insurance coverage and outcomes among hospitalized young adult trauma patients across a large number of US states. We hypothesized that Medicaid expansion has been associated with reductions in lack of insurance, in-hospital mortality, failure to rescue, and 30-day unplanned readmissions, and has increased access to rehabilitation.

    Methods
    Data Source

    This study used data from the calendar years 2012 through 2014 from the State Inpatient Databases (SID) of 14 US states. The SIDs are part of the Healthcare Cost and Utilization Project (HCUP), which is sponsored by the Agency for Healthcare Research and Quality (AHRQ). Data are derived from discharge summaries and abstracts created by hospitals for billing purposes. Each database contains all of that state’s community hospital inpatient discharge records.22Quiz Ref ID For this study, we selected 11 states that have expanded Medicaid (Iowa, Maryland, Washington, Kentucky, New Jersey, Oregon, Colorado, Nevada, Arkansas, New Mexico, and Rhode Island) and 3 that have not (North Carolina, Georgia, and Florida). We selected these states because they make their data sets available centrally through AHRQ, did not implement early Medicaid expansion statewide to low-income adults (with incomes at or less than 138% of the federal poverty level), did not implement ACA Medicaid expansion on a delayed timeframe, and had reliable data on patient races/ethnicities. Because population characteristics and access to health care differ in states that chose to expand vs not expand Medicaid,23,24 we first examined changes in insurance coverage and outcomes in just the 11 selected Medicaid expansion states. We then compared changes in coverage and outcomes between 3 selected southern states that expanded Medicaid (Arkansas, Kentucky, and Maryland) and 3 southern states that did not (North Carolina, Georgia, and Florida) in a difference-in-differences analysis. These selected southern states are more similar with regard to their population demographic and socioeconomic characteristics than expansion and nonexpansion states overall (eTable 1 in the Supplement).

    This study was ruled exempt by the institutional review board at Nationwide Children’s Hospital. We received approval to use the SIDs through a data use agreement with AHRQ. Because all data were deidentified, an informed consent procedure was not required.

    Study Population

    We studied young adults (age 19-44 years) who were hospitalized for traumatic injury. We included patients with an International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) diagnosis code in the range 800.x through 959.x. Patients with only superficial injuries, late effects of injury, or foreign bodies were excluded. The transferring hospital records of patients transferred to other short-term hospitals were also excluded, with only the admission at the receiving hospital retained. Admissions with a primary diagnosis in the coding range V50 through V58 (which denote elective surgeries and aftercare) or V67 (which specifies follow-up examinations) were also excluded. To include only patients who were subject to the policy of the state in which they were hospitalized, patients were excluded if they were not residents of the state in which they were hospitalized. Finally, patients with missing discharge disposition, sex, or primary payer data were also excluded. (This number was fewer than 200 patients.)

    Outcomes and Covariates

    Our primary outcomes were in-hospital mortality, failure to rescue,25 discharge to any rehabilitation, discharge to specific types of rehabilitation (inpatient rehabilitation facility [IRF], skilled nursing facility [SNF], or home health care agency), and unplanned readmission to an acute care hospital within 30 days of discharge. Planned readmissions (under V codes, for elective surgery and aftercare) and patients discharged and readmitted within the same day were not considered readmissions, because these primarily represented transfers to rehabilitation hospitals or rehabilitation units within acute-care hospitals. Discharge to rehabilitation could not be assessed in patients from Maryland because of a lack of detailed information on patients’ discharge disposition. Readmissions could not be assessed in patients from Kentucky, New Jersey, Oregon, Colorado, Nevada, Rhode Island, or North Carolina because of a lack of patient identifiers.

    Patient-level characteristics considered included age, sex, race/ethnicity (categorized as non-Hispanic white, non-Hispanic black, Hispanic, other, or unknown), median household income in the patient’s residential zip code (in quartiles), rurality of the patient’s home county,26 injury severity score (mild: <9, moderate: 9-15, severe: >15),27 mechanism of injury,28,29 type of injury,30,31 intentionality of injury,32 presence of a severe head injury (defined as an Abbreviated Injury Scale score >3), number of chronic conditions, presence of traumatic shock (ICD-9-CM code 958.4), and whether a surgical procedure was performed.33 Additionally, the trauma-center level of the treating hospital was considered and was defined with American Hospital Association annual survey data from the same year.34

    Statistical Analysis
    Effects of Medicaid Expansion and Open Enrollment: Analyses of Medicaid Expansion States

    Differences in patient characteristics were compared between the pre-Medicaid expansion and open enrollment (2012-2013) and post-Medicaid expansion and open enrollment (2014) periods using χ2 tests for categorical variables and Mann-Whitney or Kruskal-Wallis tests for continuous variables. Changes in the proportion of patients uninsured, covered by Medicaid, and privately insured were evaluated using marginal logistic regression models fit using generalized estimating equations, with independent correlation structure and robust variance estimation, to account for patient clustering within hospitals. Similar models were fit to compare adjusted outcomes before and after Medicaid expansion and open enrollment. All analyses were repeated in moderately to severely injured patients (those with injury severity scores ≥9). Additional subgroup analyses excluded patients with burns (ICD-9-CM codes 940.0-949.5), patients discharged in 2012, and patients aged 18 to 25 years (because this age group was eligible for the ACA’s 2010 dependent coverage provision). In all multivariable analyses, adjustment was made for patient characteristics only. Analyses were repeated with trauma center level (I, II, III, and nontrauma center) added to account for the effect of treatment at a trauma center on patient outcomes. Trauma center status was added in sensitivity analyses only because the probability of being transferred to a trauma center may be influenced by insurance status,35,36 thus treatment at a trauma center could mediate the effect of Medicaid expansion on trauma outcomes. Furthermore, trauma center status was not available for hospitals in New Mexico or Georgia. Marginal (standardized) estimates of outcomes during each period and changes in outcomes over time were calculated, with standard errors calculated using the delta method.

    Effects of Medicaid Expansion: Analyses of Medicaid Expansion vs Nonexpansion States

    Patient characteristics were compared before and after Medicaid expansion and open enrollment overall and in the selected expansion and nonexpansion states using χ2 tests for categorical variables and Mann-Whitney or Kruskal-Wallis tests for continuous variables. Difference-in-differences analyses, namely marginal logistic regression models that included an interaction term between period and a state’s Medicaid expansion status, were used to compare changes in the types of health insurance of young adults hospitalized for injury between the expansion and nonexpansion states. Risk-adjusted changes in outcomes were examined using marginal logistic regression models. Difference-in-differences models that included the prespecified patient demographic and clinical characteristics were used to compare changes in outcomes in the expansion vs nonexpansion states. All subgroup analyses performed in the 11 expansion states were repeated, and analyses were also repeated after accounting for trauma center level. Marginal estimates of outcomes during each period and differences in risk differences were calculated for all outcomes, with standard errors calculated using the delta method.

    In both analyses, no variable had a missing value in more than 5% of records, thus records with missing values for multilevel categorical variables were designated with indicator variables. Statistical analyses were conducted using SAS version 9.4 (SAS Institute Inc) and Stata/SE version 14.0 (StataCorp). Two-sided P values of less than .05 were considered significant. Data analysis was completed from April 2017 to August 2017.

    Results
    Analyses of Medicaid Expansion States

    A total of 141 187 hospitalized young adult trauma patients were included, of whom 43 871 (31.1%) patients were women. The mean (SD) age was 31.4 (7.6) years. Distributions of both sociodemographic and injury-related characteristics were relatively similar across the 2 study periods, although many slight differences (including age, sex, race/ethnicity, urban/rural residence, median household income quartile, injury severity score, number of chronic conditions, presence of traumatic shock, and hospital trauma center level, as well as some injury mechanisms, types, and intents) were statistically significant in this large study cohort (Table 1).

    Before ACA Medicaid expansion, 36 346 of the hospitalized young adult trauma patients (37.4%) were covered by private insurance, while Medicaid and uninsured patients numbered 16 229 (16.7%) and 27 016 (27.8%), respectively. Quiz Ref IDMedicaid expansion was associated with a significant increase in Medicaid coverage (difference, 18.2% [95% CI, 16.5%-20.0%]; P < .001), a slight but significant decrease in private insurance coverage (difference, −1.4% [95% CI, −2.3% to −0.4%]; P = .01), and a significant decrease in the proportion of patients uninsured (difference, −15.1% [95% CI, −16.8% to −13.5%]; P < .001). Changes were similar in the subgroup of moderate to severely injured patients (Medicaid insurance: difference, 19.1% [95% CI, 16.8%-21.4%]; P < .001; private insurance: −2.2% [95% CI, −3.7% to −0.7%]; P = .004; no insurance: −12.8% [95% CI, −16.7% to −8.9%]; P < .001) (Table 2).

    Quiz Ref IDAlthough ACA Medicaid expansion in the selected states was not associated with significant reductions in in-hospital mortality or failure to rescue, there was a significant increase in the proportion of patients able to access rehabilitation, (difference, 1.16% [95% CI, 0.55% to 1.77%]; P < .001), particularly IRFs (difference, 0.46% [95% CI, 0.13%-0.79%]; P = .01) and SNFs (difference, 0.42% [95% CI, 0.14%-0.70%]; P = .004) (Table 2). Medicaid expansion under the ACA in its first year was not associated with any change in 30-day unplanned readmissions. Similar results were seen in the subgroup of moderate to severely injured patients (IRF: difference, 1.01% [95% CI, 0.26%-1.77%]; P = .01; SNF: difference, 0.54% [95% CI, 0.02%-1.06%]; P = .04). However, in this subgroup, Medicaid expansion was associated with a slightly larger increase in discharge to rehabilitation (difference, 1.64% [95% CI, 0.46%-2.82%]; P = .01), particularly IRFs, and a marginally significant decrease in 30-day unplanned readmissions (Table 2). All results were similar in other sensitivity analyses (eTables 2-4 in the Supplement), including those adjusting for hospital trauma center level.

    Analyses of Medicaid Expansion vs Nonexpansion States

    A total of 176 122 hospitalized young adult trauma patients were included: 44 678 residents of the selected southern expansion states and 131 444 residents of the selected southern nonexpansion states. Sociodemographic and clinical characteristics were substantively similar over time in both the expansion and nonexpansion states, although many small differences (eg, in several categories of mechanism of injury, injury type, and intentionality) were statistically significant because of the large sample size (Table 3).

    Medicaid expansion under the ACA in the 3 selected southern expansion states was associated with a significant increase in Medicaid coverage (difference: 18.7% [95% CI, 15.3%-22.0%]; P < .001), a slight but significant decrease in private insurance coverage (difference-in-differences: −2.1% [95% CI, −4.0% to −0.2%]; P < .03), and a significant decrease in the proportion of patients uninsured (difference-in-differences: −18.0% [95% CI, −21.1% to −14.8%]; P < .001) (Table 4). The same was true in the subgroup of moderate to severely injured patients Medicaid insurance: difference-in-differences, 20.8% [95% CI, 16.5%-25.2%]; P < .001; private insurance: −4.2% [95% CI, −7.3% to −1.0%]; P = .01; no insurance: −18.6% [95% CI, −23.0% to −14.3%]; P < .001). Medicaid expansion was not associated with reductions in the rates of in-hospital mortality or failure to rescue. Similar to our findings in 11 geographically disperse expansion states, Medicaid expansion in the 3 selected southern states was associated with a significant increase in discharge to any type of rehabilitation (difference-in-differences: 1.86% [95% CI, 0.81%-2.90%]; P = .001). However, only discharge to SNFs increased statistically significantly (difference-in-differences: 0.54% [95% CI, 0.11%-0.96%]; P = .01). Similar effects of Medicaid expansion on access to rehabilitation were observed in moderate to severely injured patients (difference-in-differences: 3.39% [95% CI, 1.33%-5.44%]; P = .001), although in this subgroup there was a significant increase in discharge to IRFs (difference-in-differences: 1.53 % [95% CI, 0.02%-3.04%]; P = .047) (Table 4). All results were similar in other sensitivity analyses (eTables 5-7 in the Supplement), including those adjusting for hospital trauma center level.

    Discussion

    The results of this study demonstrate that, among young adult trauma patients hospitalized in 1 of 11 states that implemented ACA Medicaid expansion in January 2014, there was an 18.2% increase in the proportion of patients with Medicaid coverage, a 15.2% decrease in the proportion who were uninsured, and a 1.4% decrease in those with private insurance coverage. Quiz Ref IDIn addition, there was a 1.2% increase in discharge to rehabilitation after hospitalization but no significant decreases in in-hospital mortality, failure to rescue, or 30-day unplanned readmissions. Similar results were found when 3 of these states were contrasted with 3 geographically and demographically similar nonexpansion states. This pattern of change in insurance coverage and access to rehabilitation among hospitalized trauma patients is consistent with previous single-institution and state-specific studies that evaluated the association of ACA Medicaid expansion with outcomes in trauma patients.20,37,38

    Given that multiple studies have reported worse outcomes among uninsured patients after serious injury, it stands to reason that increasing insurance coverage might improve trauma outcomes. However, despite clear gains in insurance coverage, our study did not detect significant decreases in in-hospital mortality or failure to rescue. This finding is similar to that reported by 2 single level I trauma centers in Arizona and Oregon, but it stands in contrast to recently reported findings of decreases in in-hospital mortality and failure to rescue in the first 2 years of Medicaid expansion in the state of Maryland.17,19,20 Other than the shorter postexpansion period of our study and the single-center studies compared with the Maryland study, the reasons for these discrepant findings are unclear. However, given the wide variation in population and trauma system characteristics, government financial support for trauma centers, and Medicaid reimbursement rates across Medicaid expansion states, differing results across states are not unexpected. In addition, previous research has demonstrated lower in-hospital mortality among trauma patients treated at level I trauma centers compared with nontrauma centers after controlling for case mix.39 Although we detected no changes in patient transfer rates from before to after Medicaid expansion, there were slight decreases in the proportion of patients treated at level I trauma centers in both Medicaid expansion and nonexpansion states. However, we did not observe any significant decrease in in-hospital mortality after Medicaid expansion, even after accounting for trauma center level. Furthermore, although our analysis controlled for both patient sociodemographic and injury characteristics, there could remain unmeasured factors affecting mortality that changed over time in the selected expansion states or that differed between the selected expansion and nonexpansion states. Importantly, being uninsured is highly correlated with numerous factors that may both independently affect trauma outcomes and mediate the relationship between insurance coverage and trauma outcomes, such as poorer preinjury health status, greater treatment delay, and treatment at lower resourced hospitals.40-44 As we examined only the first year of implementation of Medicaid expansion, it is likely that many of the patients in our postexpansion cohort obtained Medicaid coverage at the time of their hospital admission, thereby reducing the influence of these potential mechanisms by which insurance coverage may affect in-hospital mortality. Although population-level growth in Medicaid enrollment was highest in the first year of ACA Medicaid expansion, rapid growth continued in 2015.45,46 This suggests that our proposed mechanisms for the association of Medicaid expansion with trauma-related mortality and readmissions may be more evident in 2016 and later. Furthermore, financial resources gained by many safety-net hospitals after Medicaid expansion would not immediately alter their resources available to trauma patients. Thus, it is possible that ACA Medicaid expansion has had a stronger association with trauma-related mortality in more recent years as general health status and access to preventive health care have improved among low-income adults in Medicaid expansion states.37,38

    Our finding of improved access to rehabilitative care is important, given the influence of rehabilitative care on the ability of seriously injured patients to regain function and restore their quality of life. A recent study comparing injured patients discharged to IRFs across Washington state with similar patients who were not discharged to an IRF found a 40% lower odds of mortality 1 year after injury among the patients who received care at an IRF. Among the patients admitted to an IRF, total functional independence scores also increased markedly, and most patients were successfully discharged home from the rehabilitation facility.47 In our analysis, we found that Medicaid expansion in its first year led to increased access to postinjury rehabilitation and specifically access to IRFs and SNFs. These findings are similar to those of the recent study of Medicaid expansion in Maryland.20

    We did not find that Medicaid expansion was associated with a decrease in unplanned readmissions among hospitalized trauma patients. Thirty-day unplanned readmission rates for trauma patients have been reported to range from 2% to 15%; these readmissions are resource intensive, and readmitted patients often experience worse outcomes, including higher mortality rates.48-50 Social deprivation and lack of follow-up outpatient care after injury are associated with a higher risk of unplanned readmissions resulting from injury complications.51,52 Uninsured patients are less likely to have access to specialized posthospital care to ensure complete recovery from injuries and the prevention of complications. However, with a sustained increase in access to all types of care under Medicaid expansion, it is possible that fewer trauma patients are being readmitted in more recent years. Future research is necessary to answer this question.

    Limitations

    Our study has several limitations, most of which result from its reliance on administrative data. As the HCUP SIDs are derived from hospital discharge data, there is some miscoding of diagnoses and procedures. However, the algorithms we used to identify trauma patients and classify types, mechanisms, and intent of injury are validated and widely used. The SIDs lack clinical detail, such as physiologic parameters, that affect the risk of in-hospital mortality and failure to rescue. The SIDs, however, are the only available databases that include information on all trauma-related hospitalizations across a large number of US states. Although the expansion states selected for our analysis represent fewer than half of the states that have expanded Medicaid to date, this restriction was necessary because of missing data on key covariates and delayed Medicaid expansion in some states. We also acknowledge the possibility that we might have detected greater associations of Medicaid expansion with insurance coverage and trauma outcomes if no included state had expanded its Medicaid program prior to 2014. However, these pre-ACA expansions affected far fewer individuals than the 2014 Medicaid expansion did.53-56 Finally, we were unable to examine the impact of Medicaid expansion in more recent years because 2015 SID data were unavailable at the time of analysis. Furthermore, additional work is needed to ensure that diagnostic code–based inclusion and exclusion criteria, injury characteristics, and outcomes are defined as consistently as possible across the transition from ICD-9 to ICD-10. Future studies are needed to examine the associations of Medicaid expansion with trauma care and outcomes in other states as well as in more recent years. In addition, given the existence of racial/ethnic and socioeconomic disparities in insurance coverage and outcomes among trauma patients,57 the association of ACA Medicaid expansion with these disparities warrants evaluation.58

    Conclusions

    This is the first multistate study of the effect of Medicaid expansion under the ACA on insurance coverage and outcomes among young adults hospitalized for injury. We found significant gains in Medicaid coverage, reductions in uninsured rates, and improved access to rehabilitation during the first year of Medicaid expansion. However, we found no significant reductions in in-hospital mortality, failure to rescue, or unplanned readmissions. As data become available, further research into the effects of Medicaid expansion on trauma care and outcomes in more recent years is warranted.

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    Article Information

    Corresponding Author: Jennifer N. Cooper, PhD, Center for Surgical Outcomes Research and Center for Innovation in Pediatric Practice, The Research Institute at Nationwide Children’s Hospital, 700 Children’s Drive, FB Ste 3A.3, Columbus, OH 43205 (jennifer.cooper@nationwidechildrens.org).

    Accepted for Publication: March 10, 2018.

    Published Online: June 6, 2018. doi:10.1001/jamasurg.2018.1630

    Author Contributions: Dr Cooper had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

    Concept and design: Minneci, Deans, Xiang, Cooper.

    Acquisition, analysis, or interpretation of data: Akande, Minneci, Deans, Cooper.

    Drafting of the manuscript: Akande, Cooper.

    Critical revision of the manuscript for important intellectual content: All authors.

    Statistical analysis: Cooper.

    Administrative, technical, or material support: Cooper.

    Supervision: Cooper.

    Conflict of Interest Disclosures: None reported.

    Funding/Support: The Research Institute at Nationwide Children’s Hospital contributed all financial and material support for this research.

    Role of the Funder/Sponsor: All of the authors of this study are employees of the funder. The funder had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

    Additional Contributions: We thank the data organizations that provided the Agency for Healthcare Research and Quality with the statewide data used for these analyses: Arkansas Department of Health, Colorado Hospital Association, Florida Agency for Health Care Administration, Georgia Hospital Association, Iowa Hospital Association, Kentucky Cabinet for Health and Family Services, Maryland Health Services Cost Review Commission, Nevada Department of Health and Human Services, New Jersey Department of Health, New Mexico Department of Health, North Carolina Department of Health and Human Services, Oregon Association of Hospitals and Health Systems, Rhode Island Department of Health, Washington State Department of Health. These organizations were compensated for these contributions by the funder of this study.

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