Urine sodium concentration to predict fluid responsiveness in oliguric ICU patients: a prospective multicenter observational study

Abstract

BackgroundOliguria is one of the leading triggers of fluid loading in patients in the intensive care unit (ICU). The purpose of this study was to assess the predictive value of urine Na+ (uNa+) and other routine urine biomarkers for cardiac fluid responsiveness in oliguric ICU patients.MethodsWe conducted a prospective multicenter observational study in five university ICUs. Patients with urine output (UO) <0.5 ml/kg/h for 3 consecutive hours with a mean arterial pressure >65 mmHg received a fluid challenge. Cardiac fluid responsiveness was defined by an increase in stroke volume >15 % after fluid challenge. Urine and plasma biochemistry samples were examined before fluid challenge. We examined renal fluid responsiveness (defined as UO >0.5 ml/kg/h for 3 consecutive hours) after fluid challenge as a secondary endpoint.ResultsFifty-four patients (age 51 ± 37 years, Simplified Acute Physiology Score II score 40 ± 20) were included. Most patients (72 %) were not cardiac responders (CRs), and 50 % were renal responders (RRs) to fluid challenge. Patient characteristics were similar between CRs and cardiac nonresponders. uNa+ (37 ± 38 mmol/L vs 25 ± 75 mmol/L, p = 0.44) and fractional excretion of sodium (FENa+) (2.27 ± 2.5 % vs 2.15 ± 5.0 %, p = 0.94) were not statistically different between those who did and those who did not respond to the fluid challenge. Areas under the receiver operating characteristic (AUROC) curves were 0.51 (95 % CI 0.35–0.68) and 0.56 (95 % CI 0.39–0.73) for uNa+ and FENa+, respectively. Fractional excretion of urea had an AUROC curve of 0.70 (95 % CI 0.54–0.86, p = 0.03) for CRs. Baseline UO was higher in RRs than in renal nonresponders (1.07 ± 0.78 ml/kg/3 h vs 0.65 ± 0.53 ml/kg/3 h, p = 0.01). The AUROC curve for RRs was 0.65 (95 % CI 0.53–0.78) for uNa+.ConclusionsIn the present study, most oliguric patients were not CRs and half were not renal responders to fluid challenge. Routine urinary biomarkers were not predictive of fluid responsiveness in oliguric normotensive ICU patients.

Doppler Renal Resistance Index for the Prediction of Response to Passive Leg‐Raising Following Cardiac Surgery

“…17,18 By specifically assessing renal blood flow, measurement of the renal RI might be more predictive of the renal fluid responsiveness. 19 It must be noted that the magnitude of the observed changes in renal RI during the PLR manoeuvre were very small and were in the order of usually reported inter-observer variability. 30 This could limit the clinical utility of this modality, especially when the Doppler evaluation is sub-optimal due to patient's body habitus or to the quality of the ultrasound apparatus.…”

“…As recently reported, some oliguric patients might be "renal fluid responders" without a significant increase in cardiac output. 19 The objective of this exploratory study was to determine if serial RI measurements in patients after cardiac surgery can predict an increase in cardiac output following passive leg-raising, a validated marker of fluid responsiveness. 20…”

Fluid management in acute kidney injury

“…AKI acute kidney injury, GFR glomerular filtration rate, RBF renal blood flow oliguric states related to acute illness are less clear. There seems to be dissociation between macrohaemodynamic response to fluid challenge and renal response; half of the oliguric ICU patients are not renal responders [20]. Therefore, the use of hypotension or oliguria alone as triggers for fluid therapy is often not fully supported by physiological reasoning.…”

A nephrologist should be consulted in all cases of acute kidney injury in the ICU: We are not sure

“…Furthermore, diagnostic work-up as taught to nephrology residents may not be applicable to ICU patients. As an example, the accuracy of the classical urinary indices for the differential diagnosis between prerenal and renal causes is disappointing in ICU patients [6]. 3.…”