Descriptors of the cardiovascular system are the pressure adjusted heart rate, lactate, intraaortic balloon pump and ventricular assist device. In our study the mean heart rate was higher in patients who survived, indicating that the heart rate is not a good predictor in cardiac surgery patients. Inotropes (epinephrine, norepinephrine, dopamine and dobutamine) were highly significant for mortality, and are a variable of the SOFA scoring system. We chose not to include the inotropes, because the combination regimens of inotropes differ between ICUs. Moreover, the dosages of inotropes may depend on volume replacement.
Cardiac index measures were only available in less than 30 % of all patients, and is therefore not an ideal variable. Mixed venous saturation showed no significant association with 30 day mortality.
Lactate proved to be one of the best predictors in postoperative cardiac patients. Most of the scoring systems were constructed at a time when lactate was not readily available. Today lactate is available in every ICU with own blood gas analysis. Davies et al. were able to demonstrate that lactate was the best predictor for intraaortic balloon pumping failure after cardiac surgery.
Many physiological changes of the cardiovascular system may be masked by intraaortic balloon pumps (IABP) and ventricular assist devices (VAD), which are commonly used in cardiac surgical patients. Including therapeutical interventions into a score has the potential disadvantage that the organ dysfunction will be described differently between centers because of different practice patterns. Higgins et al. reported an odds ratio of 7.11 in his morbidity model and an odds ratio of 4.46 in his mortality model for the postoperative IABP-usage. VADs may have even a greater impact on outcome and resource allocation compared to IABP insertion.