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

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. 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.

Survival by dialysis modality in critically ill patients with acute kidney injury.

Among critically ill patients, acute kidney injury (AKI) requiring dialysis is associated with mortality rates generally in excess of 50%. Continuous renal replacement therapies (CRRT) often are recommended and widely used, although data to support its superiority over intermittent hemodialysis (IHD) are lacking. Data from the Program to Improve Care in Acute Renal Disease (PICARD), a multicenter observational study of AKI, were analyzed. Among 398 patients who required dialysis, the risk for death within 60 d was examined by assigned initial dialysis modality (CRRT [n = 206] versus IHD [n = 192]) using standard Kaplan-Meier product limit estimates, proportional hazards ("Cox") regression methods, and a propensity score approach to account for selection effects. Crude survival rates were lower for patients who were treated with CRRT than IHD (survival at 30 d 45 versus 58%; P = 0.006). Adjusted for age, hepatic failure, sepsis, thrombocytopenia, blood urea nitrogen, and serum creatinine and stratified by site, the relative risk for death associated with CRRT was 1.82 (95% confidence interval 1.26 to 2.62). Further adjustment for the propensity score did not materially alter the association (relative risk 1.92; 95% confidence interval 1.28 to 2.89). Among critically ill patients with AKI, CRRT was associated with increased mortality. Although the results could reflect residual confounding by severity of illness, these data provide no evidence for a survival benefit afforded by CRRT. Larger, prospective, randomized clinical trials to compare CRRT and IHD in severe AKI are needed.

Timing of initiation of dialysis in critically ill patients with acute kidney injury.

Among critically ill patients, acute kidney injury (AKI) is a relatively common complication that is associated with an increased risk for death and other complications. To date, no treatment has been developed to prevent or attenuate established AKI. Dialysis often is required, but the optimal timing of initiation of dialysis is unknown. Data from the Program to Improve Care in Acute Renal Disease (PICARD), a multicenter observational study of AKI, were analyzed. Among 243 patients who did not have chronic kidney disease and who required dialysis for severe AKI, we examined the risk for death within 60 d from the diagnosis of AKI by the blood urea nitrogen (BUN) concentration at the start of dialysis (BUN < or = 76 mg/dl in the low degree of azotemia group [n = 122] versus BUN > 76 mg/dl in the high degree of azotemia group [n = 121]). Standard Kaplan-Meier product limit estimates, proportional hazards (Cox) regression methods, and a propensity score approach were used to account for selection effects. Crude survival rates were slightly lower for patients who started dialysis at higher BUN concentrations, despite a lesser burden of organ system failure. Adjusted for age, hepatic failure, sepsis, thrombocytopenia, and serum creatinine and stratified by site and initial dialysis modality, the relative risk for death that was associated with initiation of dialysis at a higher BUN was 1.85 (95% confidence interval 1.16 to 2.96). Further adjustment for the propensity score did not materially alter the association (relative risk 1.97; 95% confidence interval 1.21 to 3.20). Among critically ill patients with AKI, initiation of dialysis at higher BUN concentrations was associated with an increased risk for death. Although the results could reflect residual confounding by severity of illness, they provide a rationale for prospective testing of alternative dialysis initiation strategies in critically ill patients with severe AKI.