A preoperative and intraoperative predictive model of prolonged intensive care unit stay for valvular surgery

In developing countries, the costs of intensive care unit (ICU) stay are very high for patients after valve surgery. In addition, patients with a prolonged ICU stay have a poor prognosis compared to those with a short ICU stay. The study aim was to develop a specific risk model and to use a logistic EuroSCORE model to predict prolonged ICU stay after valve surgery.

A total of 507 consecutive patients undergoing valve surgery were studied using univariate and multivariate analyses. Prolonged ICU stay was defined as five days or more. Stepwise logistic regression analysis was used to identify the risk factors for prolonged ICU stay. These variables were then used to calculate a prognostic score (S) and a predicted probability (P) for prolonged ICU stay. A receiver operating characteristic (ROC) curve was calculated to measure the prognostic value of the new risk model and logistic EuroSCORE model. Sensitivity and specificity analysis were used for evaluation.

Multivariate logistic regression analysis showed that age > or = 65 years, left ventricular ejection fraction (LVEF) < or = 50%, cardiothoracic ratio (CTR) > or = 0.68, previous cardiac surgery, maximal voluntary ventilation (MVV) observed/predicted < 71% and repeat cardiopulmonary bypass (CPB) during surgery were risk factors. Mitral valve surgery reduced the risk of prolonged ICU stay. Observed probabilities compared well with predicted probabilities. The ROC curve produced an area under the curve (AUC) value of 0.81 for prolonged ICU stay. Based on predicted probability, patients were classified as low-risk (0 < or = P < 10%), intermediate-risk (10% < or = P < 20%), high-risk (20% < or = P < 40%) and very high-risk (> or = 40%) groups. A P-value > or = 40% was used as a cut-off point for the prognostic test. The specificity of this test was 97%, sensitivity 32%, positive predictive value 62%, negative predictive value 89%, positive likelihood ratio 10.67, and negative likelihood ratio 0.70. The ROC curve of a logistic EuroSCORE model gave an AUC value of 0.66 for prolonged ICU stay.

The study results showed that individual patients undergoing valve surgery could be stratified according to their risk factors for prolonged ICU stay. High-risk patients may require more careful preoperative and postoperative management to reduce postoperative mortality, morbidity, the length of ICU stay, and therefore the cost of valve surgery.