Urine Electrolytes in the Intensive Care Unit: From Pathophysiology to Clinical Practice

Urinary electrolyte parameters in sepsis-associated acute kidney injury: A prospective observational study

Background and Aims

Sepsis-associated acute kidney injury (SA-AKI) significantly contributes to morbidity and mortality. Current biomarkers have limitations, necessitating the exploration of alternative indicators. This study aims to evaluate various urinary electrolyte parameters to predict SA-AKI.

Methods

A prospective observational study included 111 sepsis patients within 24 h of admission. Urinary electrolyte samples were collected, and indices were calculated. Patients were monitored for 7 days to assess for acute kidney injury (AKI) according to Kidney Disease Improving Global Outcomes (KDIGO) definition criteria, mortality rates, and the need for renal replacement therapy. Mann-Whitney U test and Chi-squared test were used to analyse continuous and categorical variables, respectively. Receiver-operating characteristic (ROC) curves were constructed to determine to discriminatory ability of various parameters in predicting AKI.

Results

Of 111 patients, 42.3% developed AKI, with a mortality rate of 59.5%. When evaluating urinary parameters, the product of urine sodium and urine creatinine exhibited the maximum full form [area under the receiver operating characteristic (AUROC): 0.66; 95%CI: 0.56, 0.77)], and the parameter of fractional excretion of potassium (FeK) exhibited an AUROC of 0.62 (95%CI: 0.51, 0.72). Furthermore, 2-hour excretion of potassium revealed a statistically significant correlation with 2-hour creatinine clearance (r = 0.62, P < 0.001). Logistic regression models, incorporating Sequential Organ Failure Assessment (SOFA) score, FeK, and urine sodium concentration as variables (P = 0.020, 0.044, and 0.033, respectively), achieved an AUROC of 0.751 in predicting AKI.

Conclusion

Urine sodium levels and fractional potassium excretion moderately effectively predict AKI in sepsis patients. Urine potassium excretion correlates with glomerular filtration rate.

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.

How to cite this article

Maciel AT. Optimizing Postoperative Acute Kidney Injury Monitoring Using a Urine Biochemical Approach-Time to Bring More Dynamism to Serum Creatinine Evaluation! Indian J Crit Care Med 2024;28(8):729-733.

Screening Cases of Suspected Early Stage Chronic Kidney Disease from Clinical Laboratory Data: The Comparison between Urine Conductivity and Urine Protein

(1) Background: Chronic kidney disease (CKD) affects more than 800 million global population. Early detection followed by clinical management is among the best approaches for the affected individuals. However, a sensitive screening tool is not yet available. (2) Methods: We retrospectively reviewed 600 patients aged >20 years with a full range of estimated glomerular filtration rate (eGFR) for clinical assessment of kidney function between 1 January 2020, to 30 April 2021, at the Taichung Veterans General Hospital, Taichung, Taiwan. With stratified sampling based on the level of eGFR, participants were evenly grouped into training and validation sets for predictive modeling. Concurrent records of laboratory data from urine samples were used as inputs to the model. (3) Results: The predictive model proposed two formulae based on urine conductivity for detecting suspected early-stage CKD. One formula, P_male45, was for used male subjects aged ≥45 years, and it had a prediction accuracy of 76.3% and a sensitivity of 97.3%. The other formula, P_female55, was used for female subjects aged ≥55 years. It had a prediction accuracy of 81.9% and a sensitivity of 98.4%. Urine conductivity, however, had low associations with urine glucose and urine protein levels. (4) Conclusion: The two predictive models were low-cost and provided rapid detection. Compared to urine protein, these models had a better screening performance for suspected early-stage CKD. It may also be applied for monitoring CKD in patients with progressing diabetes mellitus.

Dual-mode ion-selective electrodes and distance-based microfluidic device for detection of multiple urinary electrolytes

Here, we developed a microfluidic paper device by combining ion-selective electrodes (ISE) and a distance-based paper device (dPAD) for simultaneous potentiometric and colorimetric detection of urine electrolytes including K+, Na+ and Cl−.