Delirium in Mechanically Ventilated Patients After Cardiac Surgery: The Importance of Preoperative Nutritional Management Revealed by a Multicenter Retrospective Cohort Study

OBJECTIVE: The effects of malnutrition on postoperative delirium (POD) after cardiac surgery remains understudied. We hypothesized that preoperative prognostic nutrition index (PNI) has a significant clinical role in predicting POD among mechanically ventilated patients undergoing cardiac surgery. METHODS: We conducted a multicenter retrospective study of adult patients who underwent cardiac surgery and subsequently received mechanical ventilation (MV) in the Intensive Care Unit at Nanjing First Hospital (NFH-ICU) and from Medical Information Mart for Intensive Care IV (MIMIC-IV). The relationship between PNI and POD was examined by Cox proportional hazards models, propensity score matching, mediation analysis, subgroup analysis, and sensitivity analysis. RESULTS: 2725 participants of NFH-ICU and 3368 participants of MIMIC-IV were included in this study. Reduced PNI levels were identified as an independent risk factor for POD, and its addition enhanced the accuracy of predicting POD. After adjusting for all confounders, Cox analysis revealed that PNI≤45.5 was significantly associated with the risk of progressing to POD (NFH-ICU: HR = 1.46, 95% CI 1.01-2.11, p = 0.044; MIMIC-IV: HR = 1.53, 95% CI 1.14-2.07, p = 0.005). We also analyzed the mediating role of duration of MV on malnutrition and POD. The proportions mediated were 31.64% and 9.71% in NFH-ICU and MIMIC-IV, respectively. CONCLUSION: The decreased PNI can increase the risk of POD after cardiac surgery. Meanwhile, the increased risk of POD associated with low PNI was partially mediated by prolonged duration of MV after surgery. The study highlights the preoperative nutritional management as an important intervention to prevent postoperative delirium in patients undergoing cardiac surgery.