Intermittent Urine Oxygen Tension Monitoring for Predicting Acute Kidney Injury After Cardiovascular Surgery: A Preliminary Prospective Observational Study

Introduction Novel biomarkers of acute kidney injury (AKI) are being developed and commercialized. However, none are universally available. The aim of this preliminary prospective observational study was to explore the effectiveness of intermittent urine oxygen tension (PuO(2)) monitoring without special equipment (using a blood gas analyzer) for predicting AKI after elective cardiovascular surgery requiring cardiopulmonary bypass (CPB). Methods Fifty patients who underwent elective cardiovascular surgery requiring CPB were enrolled in the study with written informed consent. Urine samples were intermittently collected from a urethral catheter at four points: T1, immediately after induction of general anesthesia in the operating room; T2, immediately after intensive care unit (ICU) admission; T3, six hours after ICU admission; and T4, 12 hours after ICU admission. PuO(2) was measured with a blood gas analyzer. The Kidney Disease Improving Global Outcomes classification was used for the diagnosis of AKI, then patients were followed up until postoperative day 7. By generating the receiver operating characteristic curves, the cut-off value of PuO(2) and area under the curve (AUC) for predicting the onset of AKI was calculated. The odds ratio (OR) and 95% confidence interval (CI) of each time point were calculated using logistic regression analysis or exact logistic regression method. P < 0.05 was considered significant. Results Twelve patients were diagnosed with AKI (24% morbidity). The cut-off values of PuO(2) for predicting onset of AKI at the four time points were T1, PuO(2) ≥ 132.4 mmHg (OR 3.1, 95% CI 0.78-12.0, p = 0.11, AUC 0.57); T2, PuO(2) ≥ 153.3 mmHg (OR 5.8, 95% CI 1.08-31.4, p = 0.04, AUC 0.51); T3, PuO(2) ≥ 130.1 mmHg (OR 0.19, 95% CI 0.05-0.75, p = 0.018, AUC 0.68); T4, PuO(2) ≥ 88.6 mmHg (OR 0.07, 95% CI 0-0.486, p = 0.011, AUC 0.64). Conclusion Intermittent PuO(2) values at six and 12 hours after ICU admission may be predictors of AKI, although the AUCs to predict AKI were low (0.68 and 0.64). AKI prediction by PuO(2) was not possible immediately after induction of general anesthesia (not statistically significant) and immediately after ICU admission (AUC was very low). Further studies are required to confirm the validity of intermittent PuO(2) monitoring.