Effects of Decreased Emergency
g
y Department
p
Access on AMI Health Outcomes
Presenter:
Yu-Chu Shen
Naval Postgraduate School and NBER
Co-authors:
Renee Hsia, UCSF
Laurence Baker, Stanford
We thank the Robert Wood Johnson Foundation’s HCFO Initiative grant #63974 for
financial support
B k
d
Background
Between 1995 and 2005, number of ED went
down by 23% while annual ED visits went up by
19% (NHAMCS 2007).
Decrease access to ED is well documented in
the literature.
Anecdotal reports hinting at adverse effects on
patient care, little empirical evidence.
Th
R
hQ
i
Three
Research
Questions
Does increased driving time to ED result in
increased mortality rates among AMI patients?
Does increased driving time to ED result in
changes in health profile of AMI patients who
arrived alive in the hospital?
If decreased ED access has an adverse effect
on patient outcomes, is the adverse effect
transitory or permanent?
Hypotheses on the Effect
of Increased Time to ED
on AMI Patients
• Patients who survived to have hospital records are
younger in areas with decreased ED access than
those in areas with no decrease in ED access
access.
• The observed mortality rates of all AMI patients would
increase when ED access decreases
decreases, but the
observed mortality rates of patients who survived to
have a hospital record might not.
• Patients in areas with decreased ED access arrive at
the hospital with higher probability of needing
immediate procedure.
A Hypothetical Example
Compare between two groups of patients
AMI
mortality
rates
Time to ED
did not
increase b/w
95 and 96
Time to ED Dif
increase
b/w 95 and
96
1995
1996
Dif-in-diff
14%
9%
16%
14%
2%
5%
3%
Data
• To
T identify
id tif ED availability
il bilit
– AHA surveys
– California OSHPD
• Patient data
– 100% Medicare Provider Analysis and Review
(MedPAR) and denominator file
• Location data to calculate driving time
– Mailer software (patient)
– Dr. Jill Horwitz (hospital)
• Hospital data
– Healthcare Cost Report Information System (HCRIS)
Defining AMI Outcomes
Mortality rates of different time horizon
– 7-day, 30-day, 90-day
Age and care intervention
– Age at the time of hospital admission
– Whether receive PTCA on the day of admission
Defining ED Access Change
Categories
• Control group: people who live in zip codes with no
increase in driving time to their closest ED;
• Treatment group: people who live in zip codes that
experience the following amount of increases in
driving time between 1996 and 2005.
– <10 minutes
– 10-30 minutes
– >=30
30 minutes
Empirical Approach (1)
• Identify the effects of ED access by comparing
changes in mortality outcomes and health
characteristics between control and TT groups
• Mortality rates and PTCA
– Fixed-effects linear probability model
• Age
– Fixed-effects OLS
• Robust standard errors to account for
clustering at zip code level
Empirical Approach (2)
• Control variables:
–
–
–
–
Whether nearest facility has cath lab
Patient demographics, comorbidity
Admitted hospital characteristics
Year trend
• Model 2: Add transition yyear indicators
– Timing issue: only observe closure on yearly basis
– Transitory or permanent effect
• Additional analysis
– Limit control group to those with limited access to
ED in baseline
Figure 1. Distribution of ED Access
Change on US Map
Change in driving time to nearest ED 1996‐2005
No Data
Up to 10min increase
No increase in driving time
Up to 30min increase
Up to 5min increase
More than 30min increase
Main Regression Results (1)
AMI Mortality Rates
7-day
30-day
90-day
ED Di
Distance
t
Ch
Change
C
Categories
t
i
All yrs after driving time inc by <10
0.0025
0.0034
0.0067*
0.0007
-0.0077
-0.0002
0.0102
-0.0014
-0.0028
-0.0036*
-0.0031+
-0.0025
minutes
All yrs after driving time inc 10-30
minutes
All yrs after driving tie inc by >=30
minutes
Closest facility has cath lab
Main Regression Results (2)
AMI Health Profile
Age
PTCA on day
of admission
ED Distance Change Categories
All yrs after driving time inc by <10
0.234**
0.234
-0.006*
0.006
0 265
0.265
-0
0.005
005
-0 620*
-0.620*
0 035**
0.035**
-0.048
0 048
0 003+
0.003+
minutes
All yrs after driving time inc 10-30
minutes
All yrs after driving tie inc by >=30
minutes
Closest facility has cath lab
Transition Year Indicators
(Limited ED Access in Baseline)
AMI Mortality Rates
7-day
30-day
90-day
ED Transition
T
iti Yr
Y Categories
C t
i
(-3, -2) years before change
-0.0001
0.0038
-0.0001
(-1, 0, 1) years during change
0.0046+
0.0097**
0.0085*
(2, 3) years after change
0.0068+
0.0084+
0.0090+
Discussion
• Overall, ED access deterioration only affects a
very small percent of the population
• In general, results consistent with conceptual
y
framework’s hypotheses
• Cath availability appears to be more important
than time at improving short-term
short term mortality
rates.
• Some evidence of transitory effect