A Novel Score to Estimate the Risk of Pneumonia After Cardiac Surgery

Arman Kilic, MD1, Rika Ohkuma, MD 1, J. Trent Magruder, MD1, Joshua C. Grimm, MD1, Marc Sussman, MD1,

Eric B. Schneider, PhD1, Glenn J.R. Whitman, MD1

1Division of Cardiac Surgery, Johns Hopkins Hospital, Baltimore, MDNone of the authors have any relevant financial relationships to disclose.

BackgroundPneumonia is the most common nosocomial infection

after cardiac surgery

Postoperative pneumonia is associated with increased risk of mortality and readmission, as well as prolonged ICU and hospital stay and increased costs of care

A composite risk index for estimating pneumonia risk after cardiac surgery would have clinical utility

Study Aim

To derive and validate a risk score for postoperative pneumonia after cardiac surgery

Study Design

Study Population Adult patients (18 or older) Study period: January 1, 2005 to December 31, 2012 Excluded: ECMO or heart transplant patients

Data Source Single institution series

Data Analysis

Primary OutcomePostoperative pneumonia – STS definition – “positive sputum cultures, transtracheal fluid, bronchial washings, and/or clinical findings consistent with pneumonia”

Study PopulationRandomly divided 3:1 into training and validation sets

Data AnalysisGeneration of Risk Score in the Training Set

Univariable logistic regression analysis to evaluate association between multiple preoperative and intraoperative variables and postoperative pneumonia

Variables associated with pneumonia in univariable analysis (p<0.20) and <10% missing data entered into a multivariable model

Points were assigned to significant risk factors based on the relative magnitudes of the odds ratios

Data AnalysisValidation of Risk Score in the Validation Set

Predictive accuracy of the risk score evaluated using logistic regression, area under receiver operating characteristic curve (c-index)

C-indices also compared between risk score and STS prolonged ventilation model in predicting pneumonia

Baseline Patient CharacteristicsVariable Training Set

(n=4,666)Validation Set

(n=1,556)p-value

Age (years) 61.2 ± 14.9 61.4 ± 14.7 0.69

Male 3,067 (66%) 1,020 (66%) 0.90

Body Mass Index (kg/m2) 28.8 ± 7.6 29.0 ± 9.4 0.38

Chronic Lung Disease None Mild Moderate Severe

4,053 (87%)338 (7%)184 (4%)90 (2%)

1,346 (87%)131 (8%)54 (3%)25 (2%)

0.32

Diabetes Mellitus 1,257 (27%) 404 (26%) 0.45

Hypertension 3,411 (73%) 1,112 (71%) 0.21

Dialysis Dependence 135 (4%) 38 (4%) 0.34

Serum Creatinine (mg/dL) 1.20 ± 1.10 1.18 ± 1.12 0.56

Cerebrovascular Disease 467 (10%) 177 (11%) 0.13

Peripheral Vascular Disease 473 (10%) 160 (10%) 0.87

Prior Cardiac Intervention 1,437 (31%) 486 (31%) 0.75

Cardiogenic Shock 124 (3%) 37 (2%) 0.55

Myocardial Infarction 1,294 (28%) 413 (27%) 0.36

Baseline Operative CharacteristicsVariable Training Set

(n=4,666)Validation Set

(n=1,556)p-value

Elective Case 2,886 (62%) 976 (63%) 0.54

Type of Operation Valve CABG Combined Valve and CABG Other

1,613 (35%)1,776 (38%)487 (10%)790 (17%)

534 (34%)595 (38%)172 (11%)255 (16%)

0.88

Cardiopulmonary Bypass Time (minutes)

122.1 ± 53.3 122.1 ± 55.7 0.98

Aortic Cross Clamp Time (minutes) 78.6 ± 34.5 77.9 ± 34.6 0.52

Intra-Aortic Balloon Pump 427 (9%) 127 (8%) 0.24

Timing of Intra-Aortic Balloon Pump Preoperative Intraoperative Postoperative

262 (61%)140 (33%)

25 (6%)

79 (62%)39 (31%)

9 (7%)

0.83

ResultsPostoperative pneumonia rate of 4.5% (n=282)

In-hospital mortality rate15.3% (pneumonia) versus 4.8% (no pneumonia)

p<0.001

30-day mortality rate8.0% (pneumonia) versus 4.6% (no pneumonia)

p=0.01

Multivariable Model for PneumoniaCovariate Odds Ratio (95%

Confidence Interval)P-value Points Assigned

Age ≥ 65 Years 1.40 (1.01-1.94) 0.04 3Chronic Lung Disease None Mild Moderate Severe

Reference1.97 (1.22-3.16)3.07 (1.80-5.23)3.31 (1.56-7.03)

Reference0.005

<0.0010.002

0467

Peripheral Vascular Disease 1.69 (1.11-2.56) 0.01 3

Cardiopulmonary Bypass Time >100 Minutes

1.71 (1.13-2.61) 0.01 3

Intraoperative Red Blood Cell Transfusion

1.08 (1.03-1.13) 0.002 2

Pre- or Intraoperative Intra-Aortic Balloon Pump

2.01 (1.30-3.11) 0.002 4

TOTAL POINTS POSSIBLE - - 22

*other variables included in the multivariable model but not significant predictors: hypertension, prior cardiac intervention, myocardial infarction in last 24 hours, cardiogenic shock, increasing serum creatinine, emergent operation, type of operation, increasing aortic cross clamp time, and tricuspid valve procedure

0 2 4 6 8 10 12 14 16 18 20 220

20

40

60

80

100

Risk Score

Pre

dic

ted

Pn

eu

mon

ia R

ate

(%

)

Probability of PneumoniaBased on the Training Set

Predicted Rate

95% CI for Predicted Rate

0 2 4 6 8 10 12 14 16 18 20 220

20

40

60

80

100

Risk Score

Pre

dic

ted

Pn

eu

mon

ia R

ate

(%

)

Probability of PneumoniaBased on the Training Set

Predicted Rate

95% CI for Predicted Rate

0 2 4 6 8 10 12 14 16 18 20 220

20

40

60

80

100

Risk Score

Pre

dic

ted

Pn

eu

mon

ia R

ate

(%

)

Probability of PneumoniaBased on the Training Set

Score=0

Rate=1.2%

Predicted Rate

95% CI for Predicted Rate

0 2 4 6 8 10 12 14 16 18 20 220

20

40

60

80

100

Risk Score

Pre

dic

ted

Pn

eu

mon

ia R

ate

(%

)

Probability of PneumoniaBased on the Training Set

Score=0

Rate=1.2%

Score=22

Rate=55%

Predicted Rates of Pneumonia in the Training Set by Score Categories

Score = 0 Score 1-5 Score >50

1.3

2.5

3.8

5

1.5

2.4

4.8

Risk Score Category

Pre

dic

ted

Pn

eu

mo

nia

R

ate

in

th

e T

rain

ing

Set

(%)

p=0.002

Actual Rates of Pneumonia in the Validation Set by Score Categories

Score = 0 Score 1-5 Score >50

1

3

4

5

0

2

4

Risk Score Category

Actu

al P

neu

mo

nia

Rate

in

th

e V

alid

ati

on

Set

(%)

p=0.02

Correlation Between Predicted and Actual Rates of Pneumonia

Score = 0 Score 1-5 Score >50

1.3

2.5

3.8

5

1.5

2.4

4.8

0

2

4

Risk Score Category

Pn

eu

mo

nia

Rate

(%

)

Correlation between predicted rates in training set and actual rates in validation set

r=0.70 p<0.001

Logistic regressionOdds ratio 1.32, 95% CI 1.16-1.49

p<0.001C-index

0.74 (risk score) versus 0.71 (STS prolonged ventilation model) in predicting postoperative

pneumonia

Predictive Accuracy of the Risk Score in the Validation Set

Summary Component Points

Age ≥ 65 years 3

Chronic Lung Disease None Mild Moderate Severe

0467

Peripheral Vascular Disease 3

Cardiopulmonary Bypass Time >100 Minutes 3

Intraoperative Red Blood Cell Transfusion 2

Pre- or Intraoperative Intra-Aortic Balloon Pump 4

TOTAL POINTS POSSIBLE 22

Limitations

Clinical diagnosis of pneumonia can be subjective

In-hospital pneumonia diagnoses only

Potential for other risk factors not captured in our analysis

Did not account for interrelationship between pneumonia and other postoperative complications

Conclusions

We derived and validated a risk score for postoperative pneumonia in adult patients undergoing cardiac surgery

Immediately applicable on ICU arrival Risk score may aid in identifying high risk patients, and

therefore have applications in: • clinical research stratification• targeting patients who will benefit from tailored

preoperative management

A Novel Score to Estimate the Risk of Pneumonia After Cardiac Surgery

Arman Kilic, MD1, Rika Ohkuma, MD 1, Joshua C. Grimm, MD1, J. Trent Magruder, MD1, Marc Sussman, MD1,

Eric B. Schneider, PhD1, Glenn J.R. Whitman, MD1

1Division of Cardiac Surgery, Johns Hopkins Hospital, Baltimore, MD