Urinary electrolyte monitoring in critically ill patients: a preliminary observational study.

OBJECTIVE Intensive care unit survivors and non-survivors have distinct acid-base profiles. The kidney's regulation of urinary electrolytes and the urinary strong ion difference plays a major role in acid-base homeostasis. The aim of this study was to evaluate the potential utility of daily spot urinary electrolyte measurement in acid-base and renal function monitoring. METHODS We prospectively recorded daily plasma acid-base parameters and traditional markers of renal function in parallel with spot urinary electrolyte measurements in patients with urinary catheters admitted to our intensive care unit. Patients who remained in the intensive care unit for at least 4 days with a urinary catheter were included in the study. RESULTS Of the 50 patients included in the study, 22% died during their intensive care unit stay. The incidence of acute kidney injury was significantly higher in non-survivors during the 4-day observation period (64% vs. 18% in survivors). Urinary chloride and sodium were lower and urinary strong ion difference was higher on day 1 in patients who developed acute kidney injury among both survivors and non-survivors. Both groups had similar urine output, although non-survivors had persistently higher urinary strong ion difference on all days. Survivors had a progressive improvement in metabolic acid-base profile due to increases in the plasma strong ion difference and decreases in weak acids. These changes were concomitant with decreases in urinary strong ion difference. In non-survivors, acid-base parameters did not significantly change during follow-up. CONCLUSIONS Daily assessment of spot urinary electrolytes and strong ion difference are useful components of acid-base and renal function evaluations in critically ill patients, having distinct profiles between intensive care unit survivors and non-survivors.