Fluid accumulation, recognition and staging of acute kidney injury in critically-ill patients.
BACKGROUND
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. We evaluated the effect of fluid accumulation on sCr to estimate severity of AKI.


METHODS
In 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.


RESULTS
The 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.


CONCLUSIONS
In 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.
Macedo
Etienne
E
Division of Nephrology and Hypertension, Department of Medicine, University of California San Diego San Diego, 200 West Arbor Drive, MC 8342, San Diego, CA 92103, USA. etimacedo@hotmail.com
Bouchard
Josée
J
Soroko
Sharon H
SH
Chertow
Glenn M
GM
Himmelfarb
Jonathan
J
Ikizler
T Alp
TA
Paganini
Emil P
EP
Mehta
Ravindra L
RL
D058186:Acute Kidney Injury / Q000145:classification* / Q000175:diagnosis* / Q000378:metabolism / Q000503:physiopathology; D000328:Adult; D000368:Aged; D001826:Body Fluids / Q000378:metabolism*; D003404:Creatinine / Q000097:blood; D016638:Critical Illness; D018450:Disease Progression; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012720:Severity of Illness Index
D003404:Creatinine
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