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Delirium is a postoperative complication that often occurs after cardiac surgery and prolongs the intensive care stay and in-hospital stay. The aim of the present work was to investigate the association between delirium after cardiac surgery and various clinical pre-, intra-, and postoperative factors to determine the variables with the greatest effect on the occurrence of delirium. In the entire patient cohort, delirium occurred postoperatively in 31% of cases (93 patients). From a statistical point of view, whether delirium occurs or not does not depend on whether patients have undergone ACB or valve /aortic surgery. The proportion of delirium was slightly lower in the ACB group with 28.7% (43 patients) than in the valve/aortic group with 33.3% (50 patients) (p = 0.384 for t-test and Kruskal-Wallis test).
The logistic regression analysis revealed only age as a preoperative variable with significant impact on the occurrence of delirium. With each year of life, the probability of delirium increases in ACB patients by 9.5%, in valve/aortic operations by 6.8% and in the overall patient group by 7.9%. The other preoperative variables – including the preoperative hemoglobin level and the CDT level as well as the secondary diseases (e.g., arterial hypertension, diabetes, COPD) - were not relevant for the postoperative occurrence of delirium.
Among the intraoperative factors, only the duration of the extracorporeal circulation was a predictor for delirium in the overall patient group and in the valve/aortic subgroup. If the CPB time is increased by one minute, the probability of delirium increases in the total patient group by 0.9% and in the valve/aortic group by 1.4%. All other intraoperative factors were found to be insignificant for postoperative delirium in the logistic regression analysis.
On the other hand, the COX Regression analysis revealed that the minimum paO2 value, the maximum paCO2 value and the minimum paCO2 value are significant predictors of delirium for the entire patient group. In CABG patients, the total fluid balance, the lowest body temperature and the maximum paCO2 value were found to be relevant predictors for delirium. For the valve/aortic group, the minimum paO2 value and the minimum paCO2 value were identified as relevant. Hypoxia, hypocapnia and hypercapnia during CPB increase the risk for postoperative delirium. Therefore, in order to minimize the occurrence of delirium, care should be taken to maintain blood gas levels within the recommended limits.
Among the postoperative variables the number of fresh frozen plasma units (FFP) that were transfused during CPB and during the first 48 postoperative hours, the total mechanical ventilation time, as well as the postoperative occurrence of atrial fibrillation (only in the valve/aortic group) are significant risk factors for delirium. With each transfused FFP unit, the relative probability of delirium increases for the total patient group by 14.2% and for the valve/aortic group by 14.8%. If mechanical ventilation is increased by one hour, the probability of delirium increases in the overall patient group by 1.2% and in CABG patients by 6.2%. If atrial fibrillation occurs postoperatively, the relative probability of delirium in the valve/aortic group increases by 357%.
Thus, to minimize the occurrence of delirium, the CPB time and the ventilation duration should be maintained short, bleeding should be controlled so the need for blood product transfusions stays low, and the occurrence of AF should be prevented.
The proposed delirium calculator allows early determination of the risk for delirium for each group based on the individually determined values of the predictors. Implementation of the delirium calculator immediately after the operation and before 'weaning' is initiated, allows early initiation of the antidelirant therapy when indicated, that would improve vigilance and cognitive function more quickly, reduce ventilation time and speed up postoperative recovery.