Is preoperative vitamin D level a risk factor for acute kidney injury developing after cardiopulmonary bypass?

Objective: In this study, the relationship between acute kidney injury (AKI) that developed in the early postoperative period in the patients that underwent open heart surgery with cardiopulmonary bypass (CPB) and their preoperative 25-Hydroxy Vitamin D (25-OHD) levels was investigated. 
Method: 285 patients who underwent open heart surgery with CPB between February 2018 and December 2020 were retrospectively analyzed. Ninety seven patients (71 men, 26 women) who met the criteria were included in the study. The patients were divided into 3 groups according to their preoperative 25-OHD levels as deficiency (group I, n=28), insufficiency (group II, n=42) and normal (group III, n=27).Demographic and clinical characteristics, AKI, and CPB time were compared between the groups.Kidney Disease: Improving Global Outcomes (KDIGO) guidelines were used to define postoperative AKI. 
Results: According to the KDIGO guidelines, the incidence of postoperative AKI decreased to 19% at the end of 48 hours and to 6.2% at discharge whereas it was 21% in the first 24 hours. The decrease in KDIGO AKI stages was found to be statistically significant (p=0.002). The rate of DM was found to be significantly higher in Group I (p=0.001). No statistical difference was found between AKI and 25-OHD levels at 24 hours, 48 hours and discharge. CPB time was found to be significantly higher in Group I (p=0.006). In the univariate logistic regression model created after 25-OHD groups were taken as low (group I+group II) and normal (group III), low 25-OHD levels were found to have a significant effect on the development of DM (p=0.001, OR:8.474, 95%CI 2.336 -30.303). 
Conclusion: Although we could not find a statistical relationship between AKI and preoperative 25-OHD levels in the patients that underwent open heart surgery with CPB, we believe that 25-OHD deficiency might have effects on postoperative morbidity and mortality by affecting the renocardiovascular system.