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Thesis Defence

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Christine Herman

on 31 January 2013

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Transcript of Thesis Defence

Christine Herman, MD, MSc Candidate Division of Cardiac Surgery Department of Epidemiology Dalhousie University Do Intra-operative Precursor Events Lead to Post-operative Outcomes? Introduction 1,200 cardiac surgery cases performed annually in NS Study Question Methodology Results Conclusion Coronary Artery Bypass Surgery (CABG) Aortic Valve Replacement (AVR) Cardiopulmonary Bypass (CPB) Biannual quality assurance exercises
2004 Mortality Spike
Low risk patients Continued Quality Assurance Unplanned events a result of patient or surgical factors

Easily compensated

Minimal real-time significance Precursor Events
Do intra-operative precursor events that occur in cardiac surgical patients lead to negative outcomes in the post-operative period? Case-control design
Compare occurrence of precursor events
Controls Methods Maritime Heart Center Cardiac Surgery Registry

CABG, Valve, CABG+Valve Methods
Matched group

OR note review

5 surgeons
Blinded to outcome

Identify precursors from OR note Model Cohort n=4,270 Results Age
Atrial Fibrillation
Procedure Type
Surgeon Results-Primary outcome Selection Bias
Artificial Sample Limitations Major Adverse Cardiac Events
Kidney Failure
Death Precursor Events
Difficulty Weaning from Cardiopulmonary Bypass
Incomplete Revascularization/Repair Secondary Outcomes Log odds of MACE HEMOGLOBIN * Surgeon, DM, HTN, Afib, COPD, PVD, BMI, NYHA Clinical Characteristics α= 0.05
Power 80% Sample Size Phase 2.12340 2.12345 1.23456 1.23456 Predicted probability of MACE Greedy Matching Precursor events are associated with Major Adverse Cardiac Events in patients undergoing CABG, Valve, and CABG + Valve surgery. Summary Information Bias
Dictation dependent
Recall Bias Confounding
Variations in hospital procedure
Mixed Procedure System Safeguards Precursor Event Trajectory of Opportunity Adverse Event Engineered
Person or
Procedural controls MACE No-MACE Precursor MACE No-MACE Precursor No-Precursor ? p=0.015 Knowledge creation
Contribute to literature
Well defined Precursor Events Knowledge Translation Dissemination
Research forums
Peer-reviewed publications Action
Closing the loop PREevent Initiative Development of post-operative algorithm
Mitigate consequence of precursor events

Prospective determination of Precursor rate

Combined Cardiac Surgery, Critical Care, Cardiac Anesthesia
Other institutions Thank You Questions? Acknowledgements Thesis Committee
Dr. Roger Baskett
Dr. Adrian Levy
Dr. JF Légaré Internal Validation Bootstrapping
X random samples with replacements
Estimate is the mean of X predictions

Maintain all data for model
Unlike data-splitting and cross validation
Nearly unbiased estimates with predictive accuracy
Low variance
We can estimate precision with 95% CI Precursor Events Literature sparse
Mixed procedure
Risk profiles
Not reproducible Halifax
Associated with post-operative mortality
Matched 98.4%
286 MACE : 286 No-MACE
19 variables
Clinical variables similar
Low-medium risk Sample n=3,192 Risk Adjusting
Logistic Regression Model
Age, Sex, Procedure, Urgency, Surgeon All Risk Low-Med Risk Matched Methods Bleeding Difficulty
Weaning Regrafting/
Repair Incomplete
Revasc/Repair ≥ 1 Precursor
Event OR = 1.6; 95% CI 1.1-2.3 Wong et al. Eur J Cardiothorac Surg 2006
de Leval et al. J Thorac Cardiovasc Surg 1994
de Leval J Thorac Cardiovasc Surg 2000
Herman et al. peer-reviewed abstract, 2011 No-precursor α= 0.05
Power 80% MACE rate 9.9% Predicted Risk Frequency Predicted Risk Frequency Predicted Risk Frequency Cardiac Surgery
3.5 precursor event/case
90% compensated
Death or adverse outcomes

Adverse outcomes
Minor or Major
Regardless of compensation Close the loop
Quality improvement initiative
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