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					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

 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


Patient Safety Indicators

Anesthesia Complications *

3 4 5 6

Accidental Puncture or Laceration During Procedure
Foreign Body Left In During Procedure* Hemorrhage or Hematoma Wound Dehiscence Infection Due to Medical Care


Pulmonary Embolism and Deep Vein Thrombosis

* Labeled as medical errors

Patient Safety Indicators (cont.)

Iatrogenic Pneumothorax*


Acute Respiratory Failure

10 Sepsis 11 Physiologic and Metabolic Derangements 12 Transfusion Reaction 13 Hip Fracture*

14 Decubitus Ulcer*

* Labeled as medical errors

 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 Live discharge Death during index admission
Readmission Death during readmission N

PSI=1 63.03%
5.97% 28.32%

0.86% 14.14%



Average Costs
Index Hospitalization Readmission

Total Costs

PSI=0 PSI=1 Difference

$12,579 $31,096 147%

$17,927 $33,445 87%

$15,198 $41,510 173%

 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=1 % Difference

1.96% 1.04%*

5.2% 1.8%*

2.8% 1.4%*

* Significantly different from zero at the 99% level

Simulation Results: Outcomes (cont.)
Probability of readmission

PSI=0 PSI=1 Difference

15.1% 20.1% 5.0%*

* Significantly different from zero at the 99% level

Simulation Results: Costs
Index Hospitalization Readmission

Total Costs


$12,801 $21,190 $8,388* (232) 65.5%

$18,264 $26,198 $7,933* (529) 43.4%

$15,618 $26,607 $10,989* (284) 70.4%

% Difference

 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

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