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] °C, p = 0.035), highest noradrenaline support (0.11 [0.00–0.69] vs 0.07 [0.00–0.42] μg/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.