Plasma, Urinary, and Salivary Total Redox Status in Critically Ill Patients with Brain Injury and Secondary Organ Failure

Little is known about the clinical utility of blood, salivary, and urinary redox biomarkers in critically ill patients with brain injury and secondary organ failure. The aim of the study was to explore total antioxidant and oxidant status in neurocritically ill patients using ferric reducing antioxidant power (FRAP), total antioxidant capacity (TAC), and total oxidant status (TOS) in plasma, saliva, and urine from the study (n = 45) and the healthy control group (n = 49). We analyzed the relationship between well-known biomarkers of organ function and redox status in different biofluids. Plasma FRAP was significantly higher (p < 0.05), but salivary and urinary FRAP were statistically lower in the study group (p < 0.05, p < 0.001) compared with controls. The salivary and urinary TAC were statistically lower (p < 0.05, p < 0.001), while plasma TOS was significantly higher (p < 0.05) in the study group compared with the control group. Circulating redox status did not differ between survivors and non-survivors. Significant associations were observed in non-survivors: salivary TAC correlated with urea and creatinine; salivary FRAP with creatinine, troponin, and CRP; urinary TAC with troponin and P_aO₂/FiO₂ ratio, as well as plasma FRAP with P_aO₂/FiO₂ ratio. The plasma FRAP had a significant effect on survival (AUC = 0.687, p = 0.02), with 69% sensitivity and 83% specificity. Crucial differences in redox status in blood, saliva, and urine were observed between neurocritically ill patients and healthy controls; however, none of the biomarkers differed between survivors and non-survivors. Oxidative and antioxidant status correlated with organ function in non-survivors.