Variable selection for the classification of postoperative cardiac patients

A set of 13 extensively used hemodynamic, ventilatory and gas analysis variables are measured (on-line or off-line) on 200 patients in an intensive care unit (ICU) during the 6 h immediately following cardiac surgery. Since the existence of two well-separated classes of low- and high-risk patients has been previously shown the divergence criterion is then used to identify those variables which, at three equidistant observation times, possess the greatest separation power. Such variables always include the cardiac index (CI), representative of cardiac performance, and two indices related to respiratory efficiency and metabolic rate, i.e. the carbon dioxide production index (VCO2I) and the arterio-venous oxygen difference (avO2D). The Fisher linear classifier, utilizing these three features, is then tested by using the rotation method. The results show good performance of the linear classifier, which exhibits a probability of correct recognition always greater than 87%, thus suggesting the possibility of obtaining interesting improvements by means of more sophisticated classifiers.