Association of direct bilirubin level with postoperative outcome in critically ill postoperative patients

Background Hyperbilirubinemia is a common postoperative complication. Elevated direct bilirubin (D-Bil) and indirect bilirubin (I-Bil) levels are related to different pathophysiologies; therefore, their associations with outcomes also differ. However, there have been few comparative studies of such associations in postoperative patients. Methods This retrospective study compared the associations of postoperative D-Bil and I-Bil with outcomes. We included adult patients requiring postoperative intensive care for more than 48 hours between 2008 and 2013, except those undergoing liver operations. The number of patients was determined using a power calculation. D-Bil and I-Bil measurements were obtained on postoperative days (POD) 1 and 2. The primary outcome was defined as hospital mortality, with the number of ICU-free survival days (IFSD) at POD 28 as the secondary outcome. Results The study population consisted of 1,903 patients with a mortality rate of 2.2%. D-Bil at POD 1 was significantly higher in non-survivors than survivors (P = 0.001), but I-Bil at POD 1 showed no such relation (P = 0.209). Multivariate logistic analysis indicated that higher postoperative D-Bil was independently associated with increased postoperative mortality (POD 1: adjusted odds ratio [OR] = 2.32, P < 0.001; POD 2: adjusted OR = 1.95, P < 0.001), but I-Bil showed no such relation (POD 1: P = 0.913; POD 2: P = 0.209). Increased D-Bil was independently associated with decreased IFSD at POD 28 (POD 1: adjusted coefficient = -1.54, P < 0.001; POD 2: -1.84, P < 0.001). In contrast, increased I-Bil at POD 1 was independently associated with increased IFSD at POD 28 (POD 1: adjusted coefficient = +0.39, P = 0.021; POD 2: +0.33, P = 0.080). Conclusions D-Bil indices have a higher capability than I-Bil for predicting poorer outcomes in critically ill postoperative patients.