Fractional excretion of potassium in the course of acute kidney injury in critically ill patients: potential monitoring tool?

Abstract

Objective To evaluate the behavior of fractional excretion of potassium in the course of acute kidney injury in critically ill patients.Methods As part of a larger study in which we have evaluated blood and urinary parameters in the course of acute kidney injury, 168 patients were included. Blood and urine samples were collected daily until the removal of the urinary catheter or the initiation of renal replacement therapy. We describe the evolution of fractional excretion of potassium based on whether acute kidney injury was diagnosed, its duration (transient or persistent) and its severity (creatinine-based Acute Kidney Injury Network - AKIN stage). The diagnostic performance of fractional excretion of potassium in predicting the duration of acute kidney injury and the need for renal replacement therapy on the day of acute kidney injury diagnosis was also evaluated.Results Fractional excretion of potassium was significantly higher in persistent acute kidney injury compared to transient acute kidney injury on the day of acute kidney injury diagnosis (24.8 vs. 13.8%, p<0.001). Both groups had the median fractional excretion of potassium increasing in the two days preceding the acute kidney injury diagnosis. Patients without acute kidney injury had stable low fractional excretion of potassium values. The fractional excretion of potassium was fairly accurate in predicting persistent acute kidney injury (area under the curve: 0.712; 95% confidence interval: 0.614-0.811; p<0.001) on the day of acute kidney injury diagnosis. The area under the curve was 0.663 (95% confidence interval: 0.523-0.803; p=0.03) for renal replacement therapy. The fractional excretion of potassium increased with maximum AKIN stage reached, in both transient and persistent acute kidney injury.Conclusion Sequential fractional excretion of potassium assessment appears to be useful in critically ill patients at risk for acute kidney injury.

Simple blood and urinary parameters measured at ICU admission may sign for AKI development in the early postoperative period: a retrospective, exploratory study

“…Distinct from FENa, which seems to be of no value in AKI monitoring, 16 FEK was recently described as a valuable monitoring tool. 6 This finding was confirmed by the fact that low FEK values (< 10% 12 ) were only present in patients with low sCr ( Figure 3C), being a specific marker of normal renal function similar to very high NaU values, as previously demonstrated. 17 Low FEK and high NaU may actually represent a less activated sympathetic and renin-angiotensin-aldosterone systems, both implicated in AKI pathophysiology.…”

“…DFEK as a valuable predictive parameter is questionable because most AKI were diagnosed at D1, the same day that DFEK was calculated. Nonetheless, it brought important insights in AKI pathophysiology since, in agreement with two previous studies, 6,15 it demonstrates that the behavior of FEK is directly related to renal function remaining high (or even increasing) in AKI and low (or rapidly decreasing) in no-AKI. Finally, for the practical purpose of this study, D0 was considered the ICU admission and not the day of AKI diagnosis, a fact that might have reduced the homogeneity of the data of AKI patients in the subsequent days (e.g., a patient may have AKI resolving at D2 and another patient may have AKI diagnosed at D2).…”

“…5 In that study, AKI development was characterized by increases in the strong ion gap (SIG) and serum phosphate besides decreases in urinary sodium (NaU), chloride (ClU) and increases in urinary strong ion difference (SIDu), alterations which preceded increases in serum creatinine (sCr) and decreases in urine output. In another complementary study, 6 we have suggested that increases in the fractional excretion of potassium (FEK) may be surrogates of decreases in glomerular filtration rate (GFR) and also precede increases in sCr. Of note, in these previous studies, 5,6 most of the patients had a medical reason for ICU admission.…”

“…In another complementary study, 6 we have suggested that increases in the fractional excretion of potassium (FEK) may be surrogates of decreases in glomerular filtration rate (GFR) and also precede increases in sCr. Of note, in these previous studies, 5,6 most of the patients had a medical reason for ICU admission. Surgical patients, however, are expected to have a more precise and homogeneous moment that AKI is usually triggered, which is the surgical procedure itself.…”

Back to Basics: Is There a Good Reason to Not Systematically Measure Urine Creatinine in Acute Kidney Injury Monitoring?

“…Biochemical parameters such as urine sodium [11,12] and the fractional excretion of potassium [13] have been recently proposed to be of help in AKI monitoring, changing before significant increases in sCr. In conjunction with creatinine excretion, systematic assessment of urine electrolytes may signal to some degree of stress to the kidneys and alert to a situation of greater risk of AKI development [14].…”