Validity of scoring systems to predict risk of prolonged mechanical ventilation after coronary artery bypass graft surgery

Study objective: Two scoring systems, (the Spivack scoring system [SSS] and the cardiac risk score [CRS]), have been proposed to predict the risk of prolonged mechanical ventilation (PMV) after coronary artery bypass graft surgery (CABG). The primary objective of this study was to validate the efficacy of these scoring systems to predict the risk of PMV. Design: Prospective observational study. Setting: Cardiovascular surgical ICU. Patients: Three hundred forty-eight patients underwent CABG. Following surgery, patients were extubated by a standardized respiratory weaning protocol. Measurements and results: Forty-nine percent of patients had SSS > 0 and had significantly longer duration of mechanical ventilation. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the SSS for failure to extubate at 48 h are 80, 49, 9%, and 98%, respectively. Two hundred thirty-two patients (67.5%), 101 patients (29%), and 12 patients (3.5%) had a CRS of 0 to 4, 5 to 8, and > 8, respectively. Patients with lower scores had shorter duration of mechanical ventilation. The sensitivity, specificity, PPV, and NPV of the CRS for failure to extubate at 10 h are 42, 73, 47% and 69%, respectively. Conclusion: The SSS may be used as a preoperative screening tool. A simple questionnaire that includes history of unstable angina, diabetes, congestive heart failure, and smoking prior to hospital admission can be used to calculate the SSS. Patients with SSS ≤ 0 are at low risk for PMV and can proceed to surgery without further evaluation.