Adverse Patient Safety Events: Costs of
Readmissions and Patient Outcomes Following
Discharge
Didem M. Bernard, Ph.D.
William E. Encinosa, Ph.D.
Patient Safety Events
 IoM estimated that between 44,000 and
98,000 people die in hospitals each year as a
result of medical errors
 Medical errors is the eighth leading cause of
death in the U.S.
 IoM recommended at least a 50% reduction in
medical errors over 5 years
Background
 Medical injuries during hospitalizations lead to
excess length of stay, charges and mortality
(Zhan and Miller, 2003)
 Whether adverse patient safety events have a
significant impact on patient outcomes and
costs following discharge is less clear
Research Questions
Do adverse patient safety events during
hospitalizations have an effect on patient
outcomes following discharge?
Are there long-term costs associated with
potentially preventable adverse medical
events?
Patient Safety Indicators
 We use the AHRQ Patient Safety Indicators (PSI)
developed by the UCSF- Stanford Evidence-Based
Practice Center (EPC) and UC-Davis (2003).
 EPC selected 14 indicators among 63 complication
indicators using
– Indicator validity results from the literature
– Empirical analyses of the precision and reliability
of the candidate PSIs
– Review of potential indicators by 11 clinical
panels
Patient Safety Indicators
1
Anesthesia Complications *
2
Accidental Puncture or Laceration During Procedure
3
Foreign Body Left In During Procedure*
4
Hemorrhage or Hematoma
5
Wound Dehiscence
6
Infection Due to Medical Care
7
Pulmonary Embolism and Deep Vein Thrombosis
* Labeled as medical errors
Patient Safety Indicators (cont.)
8
Iatrogenic Pneumothorax*
9
Acute Respiratory Failure
10 Sepsis
11 Physiologic and Metabolic Derangements
12 Transfusion Reaction
13 Hip Fracture*
14 Decubitus Ulcer*
* Labeled as medical errors
Data
 2002 California Hospital Discharge Data
AHRQ Healthcare Cost and Utilization Project
(HCUP) State Inpatient Database (SID)
 Hospital Inpatient Cost to Charge Ratios
 Area Wage Index (CMS)
 Number of Hospitals: 349
Analytic Sample and Methods
 Major Surgery Discharges (17<age<65)
From February 1, 2002 to November 30, 2002
 Index admission: A major surgery admission with no
hospitalizations in a 30 day window prior to the
admission date (N=602,361)
 Readmission: Any hospitalization within 30 days of
initial discharge
Patient Outcomes
 Probability of readmissions
 Probability of death during index admission
 Probability of death during any readmission within 30
days of initial discharge
Costs of Adverse Patient Safety Events
 Index admission costs
 Costs of readmissions
 Total costs for index admissions and readmissions
within 30 days following discharge
Basic Model: Hospital Costs
i=person
y= cost of hospitalization*
PSI= (0,1) indicator equals 1 if patient has at least one
adverse patient safety event
x=control variables
* Index admission, readmission or total hospital costs
Basic Model: Patient Outcomes
i=person
y=(0,1) indicator equals 1 if patient is readmitted within
30 days of discharge*
PSI= (0,1) indicator equals 1 if patient has at least one
adverse patient safety event
x=control variables
* y=(0,1) indicator equals 1if patient dies during hospitalization
Control Variables
 Patient: age, sex, race/ethnicity, transfer admission,
emergency admission, 30 chronic conditions, MDC,
zipcode level median household income
 Hospital: teaching status, ownership type, bedsize
 Market: Health Service Area dummies
Patient Outcomes
PSI=0
PSI=1
Live discharge
Death during
index admission
84.55%
63.03%
0.86%
5.97%
Readmission
Death during
readmission
14.14%
28.32%
0.46%
2.68%
N
583,836
18,889
Average Costs
Index
Hospitalization Readmission
Total Costs
PSI=0
$12,579
$17,927
$15,198
PSI=1
$31,096
$33,445
$41,510
Difference
147%
87%
173%
Estimation
 Costs: GLM (Generalized Liner Method) log-link
with Gamma distribution (Manning and Mullahy,
2001)
 Patient Outcomes: Logit regressions
 Simulation results:
A : Predicted costs/outcomes with PSI=1
B : Predicted costs/outcomes with PSI=0
(A – B) : Predicted costs/outcomes due to adverse
patient safety events
Simulation Results: Outcomes
Death
during index
hospitalization
Death during
readmission
Death within
30 days of
discharge
PSI=0
0.92%
3.4%
1.4%
PSI=1
1.96%
5.2%
2.8%
% Difference
1.04%*
1.8%*
1.4%*
* Significantly different from zero at the 99% level
Simulation Results: Outcomes (cont.)
Probability of
readmission
PSI=0
15.1%
PSI=1
20.1%
Difference
5.0%*
* Significantly different from zero at the 99% level
Simulation Results: Costs
Index
Hospitalization Readmission
Total Costs
PSI=0
$12,801
$18,264
$15,618
PSI=1
PSI COST
$21,190
$8,388*
(232)
$26,198
$7,933*
(529)
$26,607
$10,989*
(284)
% Difference
65.5%
43.4%
70.4%
Summary
 Excess costs and adverse outcomes of
adverse patient safety events are not limited
to the initial hospitalization
 Adverse patient safety events during
hospitalizations lead to
– Higher probability of readmissions
– Higher probability of in-hospital death
following discharge
– Higher inpatient costs following discharge
Policy Implications
A reduction in adverse patient safety events
will not only improve quality of care but also
reduce long-term health care costs