Fluid accumulation, recognition and staging of acute kidney injury in critically-ill patients

Etienne Macedo,Glenn M Chertow,Josee Bouchard,Sharon H Soroko,Jonathan Himmelfarb,Emil P Paganini,Ravindra L Mehta,T Alp Ikizker

doi:10.1186/cc9004

Abstract

IntroductionSerum creatinine concentration (sCr) is the marker used for diagnosing and staging acute kidney injury (AKI) in the RIFLE and AKIN classification systems, but is influenced by several factors including its volume of distribution. We evaluated the effect of fluid accumulation on sCr to estimate severity of AKI.MethodsIn 253 patients recruited from a prospective observational study of critically-ill patients with AKI, we calculated cumulative fluid balance and computed a fluid-adjusted sCr concentration reflecting the effect of volume of distribution during the development phase of AKI. The time to reach a relative 50% increase from the reference sCr using the crude and adjusted sCr was compared. We defined late recognition to estimate severity of AKI when this time interval to reach 50% relative increase between the crude and adjusted sCr exceeded 24 hours.ResultsThe median cumulative fluid balance increased from 2.7 liters on day 2 to 6.5 liters on day 7. The difference between adjusted and crude sCr was significantly higher at each time point and progressively increased from a median difference of 0.09 mg/dL to 0.65 mg/dL after six days. Sixty-four (25%) patients met criteria for a late recognition to estimate severity progression of AKI. This group of patients had a lower urine output and a higher daily and cumulative fluid balance during the development phase of AKI. They were more likely to need dialysis but showed no difference in mortality compared to patients who did not meet the criteria for late recognition of severity progression.ConclusionsIn critically-ill patients, the dilution of sCr by fluid accumulation may lead to underestimation of the severity of AKI and increases the time required to identify a 50% relative increase in sCr. A simple formula to correct sCr for fluid balance can improve staging of AKI and provide a better parameter for earlier recognition of severity progression.

Highlights

Serum creatinine concentration is the marker used for diagnosing and staging acute kidney injury (AKI) in the RIFLE and Acute Kidney Injury Network (AKIN) classification systems, but is influenced by several factors including its volume of distribution
Median cumulative fluid balance increased from 2.7 L (IQR 0.5 to 6.2) on day 2 to 6.5 L (IQR 1.1 to 11.3) on day 7 (Table 1). Serum creatinine concentration (sCr) concentrations adjusted for fluid balance were significantly higher at each time point and the difference from median crude and adjusted values progressively increased from 0.09 mg/dL to 0.65 mg/dL
As the assessment of AKI is largely based on changes in sCr, we extended the observations of Moran and Myers using a cohort of critically-ill patients with AKI

Summary

Introduction

Serum creatinine concentration (sCr) is the marker used for diagnosing and staging acute kidney injury (AKI) in the RIFLE and AKIN classification systems, but is influenced by several factors including its volume of distribution. Minimal increases in serum creatinine (sCr) concentration are recognized as clinically significant events and the severity of AKI has been associated with a progressive increase in mortality [6-8]. Current diagnostic and staging criteria for AKI are based on changes in sCr and require sequential measurements [9,10]. In addition to its dependence on creatinine generation and clearance (reflecting muscle mass breakdown and kidney function, respectively), the accuracy of sCr measurements as a reflection of kidney function depends on TBW. Higher TBW results in lower sCr, which can lead to underestimation of severity of kidney injury

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