Intra-operative events during cardiac surgery are risk factors for the development of delirium in the ICU

Background: Risk factors for delirium following cardiac surgery are incompletely understood. The aim of this study was to investigate whether intra-operative pathophysiological alterations and therapeutic interventions influence the risk of post-operative delirium. Methods: This retrospective cohort study was performed in a 12-bed cardiosurgical intensive care unit (ICU) of a university hospital and included patients consecutively admitted after cardiac surgery during a 2-month period. The diagnosis of delirium was made clinically using validated scores. Comparisons between patients with and without delirium were performed with non-parametric tests. Logistic regression was applied to identify independent risk factors. Results are given as number (percent) or median (range). Results: Of the 194 consecutive post-cardiac surgery patients, 50 (26 %) developed delirium during their ICU stay. Univariate analysis revealed that significant differences between patients with and without delirium occurred in the following intra-operative variables: duration of cardiopulmonary bypass (184 [72-299] vs 113 (37-717) minutes, p < 0.001), lowest mean arterial pressure (50 [30-70] vs 55 [30-75] mmHg, p = 0.004), lowest haemoglobin level (85 [56-133] vs 98 [53-150] g/L, p = 0.005), lowest body temperature (34.5 [24.4-37.2] vs 35.1 [23.9-37.2] degrees C, p = 0.035), highest noradrenaline support (0.11 [0.00-0.69] vs 0.07 [0.00-0.42] mu g/kg/minute, p = 0.001), and frequency of red blood cell transfusions (18 [36 %] vs 26 [18 %], p = 0.018) and platelet transfusions (23 [46 %] vs 24 [17 %], p < 0.001). Only platelet transfusions remained an independent risk factor in the multivariate analysis (p < 0.001). Conclusions: In patients undergoing cardiac surgery, various intra-operative events, such as transfusion of platelets, were risk factors for the development of a post-operative delirium in the ICU. Further research is needed to unravel the underlying mechanisms.