Optimizing Postoperative Acute Kidney Injury Monitoring Using a Urine Biochemical Approach—Time to Bring More Dynamism to Serum Creatinine Evaluation!

Glomerular filtration rate (GFR) impairment is common both intraoperatively and in the early postoperative period of major surgeries, even elective ones. In some patients, such impairment is subtle and short-lasting, not even detected by increases in serum creatinine (sCr) and, consequently, not of sufficient magnitude to fulfill acute kidney injury (AKI) sCr-based criteria. In patients with a GFR decrease of greater magnitude, significant increases in sCr will occur but, unfortunately, usually at a late time in its progression. Both urinary and serum biomarkers have been proposed to be capable of anticipating AKI development but they are not widely available nor cost-effective in most centers. In this context, a urine biochemical approach using urinary sodium concentration (NaU) and the fractional excretion of potassium (FeK) has been proposed, anticipating the level of renal microcirculatory stress and decreases in GFR. An educational postoperative case example is presented highlighting the relevance that this approach can have in the correct interpretation of sCr values, bringing more dynamism to renal function monitoring.