Changes in classification criteria and active introduction of biomarkers of acute kidney injury (KDIGO, 2012) are changing approaches to diagnosis and treatment of postoperative renal dysfunction including cardiac surgery patients operated with cardiopulmonary bypass (CPB). The objective: to compare the detection rate of AKI after surgery with CPB with the use of biomarkers and kidney disease improving global outcomes criteria, as well as to evaluate the cause and localization of structural changes of the nephron.Subjects and Methods. A monocenter observational study among elective cardiac surgery patients (n = 97) was conducted. Inclusion criteria: age over 18 years, duration of surgery (coronary bypass surgery, prosthetic heart valves) from 90 to 180 minutes, no signs of end stage kidney disease. AKI was diagnosed based on changes in serum creatinine and biomarkers (NGAL, IgG, albumin in urine). The studied parameters were recorded 15 minutes after the start and end of anesthesia, as well as 24 and 48 hours after surgery. Retrospectively, the group was divided into three subgroups: 1) patients without AKI after surgery; 2) patients in whom signs of AKI were detected after 24 hours but regressed by the 48th hour; 3) patients in whom AKI persisted during all 48 hours of follow-up.Results. 24 hours after surgery, AKI based on KDIGO criteria was recorded in 56.3% of patients. Using biomarkers, signs of tubular damage (NGAL) at the end of anesthesia were detected in 95.9% of patients; after 24 hours, they were registered in 73.2% of cases. In a subgroup where AKI persisted for more than 24 hours, glomeruli were damaged in addition to tubules which was manifested not only by selective but also by non-selective proteinuria. The duration of CPB, hemodilution (Hb < 90 g/l), the release of free hemoglobin in the blood (> 1.5 mg/l) at low (< 1 g/l) values of haptoglobin were significantly associated with AKI development.Conclusion. The KDIGO criteria do not allow detecting a subclinical form of renal dysfunction which may occur in about 40% of patients after surgery with CPB. AKI can be caused by damage to both the tubular part of the nephron and glomeruli in cases of prolonged CPB with the development of hemolysis, the release of free hemoglobin in the blood, and persisting anemia at the end of the surgery. The NGAL assessment makes it possible to detect subclinical kidney injury in the absence of elevated serum creatinine levels.
Kidney Tubular Damage and Functional Biomarkers in Acute Kidney Injury Following Cardiac Surgery