Chronic on Acute Renal Failure

Abstract

EVERY YEAR MORE THAN 1 MILLION HOSPITALIZATIONS in the United States are complicated by acute kidney injury, accounting for an estimated $10 billion in excess costs to the health care system. Acute kidney injury has been shown to be a potent predictor of excess length of stay, morbidity, and mortality in a number of clinical settings. The incidence of acute kidney injury has increased more than 4-fold since 1988 and is estimated to have a yearly population incidence of more than 500 per 100 000 population—higher than the yearly incidence of stroke. Survival from an episode of acute kidney injury may be increasing by virtue of advances in critical care medicine and dialysis technologies. In short, more hospitalized patients are being discharged alive after an episode of acute kidney injury. The report by Wald and colleagues in this issue of JAMA provides valuable insights into the complex complications faced by survivors of an episode of severe acute kidney injury. Using linked administrative health databases covering the entire province of Ontario, Canada, the authors addressed the long-term risks of death and dialysis dependence among individuals who developed acute kidney injury requiring acute temporary dialysis during hospitalization. During a 10-year period between 1996 and 2006, they identified 18 551 individuals with acute kidney injury requiring dialysis, which corresponds to an approximate yearly incidence of 19 per 100 000 population—lower than the estimate of 24.4 per 100 000 population reported in Northern California between 1996 and 2003. After excluding 3321 individuals who had previous acute kidney injury, dialysis, or kidney transplantation in the preceding 5 years, and 202 who had extreme lengths of hospital stay, the authors identified 15 028 patients with a first hospitalization for acute kidney injury requiring dialysis. More than 40% of these individuals died during hospitalization, in keeping with previous reports of the grave implications of severe acute kidney injury. Nearly half of these patients recovered kidney function for at least 30 days following hospitalization, attesting to the remarkable ability of the kidneys to repair and regenerate even after severe, dialysis-requiring injury. Another 23% of patients required further dialysis within 30 days of discharge, but it is not reported how many of those required chronic dialysis. The final study cohort included 4066 survivors, 3769 (92.7%) of whom were matched to control patients and observed for a median of 3 years after discharge. Even among this selected cohort of survivors, mortality rates exceeded 10% per year. One of every 12 survivors of acute kidney injury requiring acute dialysis required subsequent initiation of chronic dialysis despite being dialysis-free at 30 days after discharge. These findings are noteworthy even without considering the next step in the analysis, which was to compare this incidence rate against that of matched individuals without acute kidney injury. From the perspective of a clinician caring for an individual with severe acute kidney injury, the findings by Wald et al provide an important quantitative estimate that can be shared with affected patients and their families: even in the best of circumstances—meaning survival during hospitalization and recovery of kidney function sufficient to stop dialysis for a month—there is almost a 10% chance of requiring chronic dialysis in the next few years. The chronic dialysis incidence rate reported by Wald et al is 72 times higher than that reported for the general population in the United States in 2006 (366/1 million person-years). This finding has important implications for the postdischarge care of patients successfully treated with acute temporary dialysis: follow-up care with a nephrologist for secondary prevention is absolutely necessary. These findings also highlight the magnitude of the problem of acute kidney injury as a cause of end-stage renal disease (ESRD): extrapolating from the data of Wald et al, a rough estimate of the yearly incidence of ESRD due to acute kidney injury is 0.3 per 100 000 population, which is approximately onethird of the incidence of ESRD secondary to cystic kidney disease. The true magnitude is even higher because this estimate does not consider the 3481 individuals excluded from the final cohort because of the need for dialysis during the