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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