While the prevalence of key risk factors for acute kidney injury (AKI) has risen over the past decade, the incidence of the condition in patients hospitalized with acute myocardial infarction (AMI) actually has decreased. This was the conclusion of a study published in Archives of Internal Medicine (2012;172:246–253).
"Over the last several years, we have tried to increase the awareness of AKI by standardizing the definition," said study coauthor Chirag R. Parikh, MD, PhD, Associate Professor of Medicine in the Section of Nephrology at Yale School of Medicine.
"At the same time, some efforts have taken place in terms of clinician awareness and using better hospital processes to reduce AKI. We wanted to see the impact of all of these things on the incidence of AKI."
Amit P. Amin, MD, MSc, of the Department of Cardiovascular Medicine at St. Luke's Hospital in Kansas City, MO, was the lead author.
The researchers used data from 56 participating US hospitals in Cerner Corporation's Health Facts database to examine time trends in AKI incidence between Jan. 1, 2000, and Dec. 31, 2008. Evaluated in the study were 33,249 consecutive hospitalizations in 31,532 unselected patients with AMI.
Overall, the incidence of acute kidney injury was 22.5%, and the crude incidence declined significantly from 26.6% in 2000 to 19.7% in 2008.
Over the same time period, risk factors for AKI became more common, including mean age (66.5 vs 68.6 years), cardiogenic shock (4.3% vs 5.7%), chronic kidney disease (3.9% vs 12.7%), coronary angiography (59.0% vs 70.0%), diabetes mellitus (30.3% vs 35.1%), heart failure (29.8% vs 32.7%), and percutaneous coronary intervention (32.1% vs 47.0%).
After adjustment for potential confounders and changes in practice patterns that could bias the results, a 4.4% decline in AKI per year persisted. In-hospital mortality among patients with acute kidney injury also declined, from 19.9% in 2000 to 13.8% in 2008.
"I very much agree that the awareness of AKI has become quite evident over the last decade," said Mark D. Okusa, MD, John C. Buchanan Distinguished Professor of Medicine and Chief of the Division of Nephrology at the University of Virginia School of Medicine.
"Much effort has been put into understanding what is needed to make improvements in AKI outcomes. I think these patients are getting more attention."
NAC or Not
In a secondary analysis, temporal trends were observed in the use of medications potentially related to AKI development.
Diuretic use decreased from 56.4% in 2000 to 47.0% in 2008, while administration of N-acetylcysteine (NAC) went up from 0.6% in 2000 to 10.6% in 2008.
"There is always a lag time with stopping an agent, especially if no one has shown that it has been detrimental," said Joseph Bonventre, MD, PhD, Samuel A. Levine Professor of Medicine and of Health Sciences and Technology at Harvard Medical School. "My feeling is it is not effective."
Dr. Okusa gave another viewpoint. "NAC is relatively inexpensive, and we think that NAC is relatively safe, especially when given orally, so, despite the absence of definitive efficacy data, it is not unreasonable to give oral NAC prophylactically to prevent AKI," he said. "There is a good biological rationale for its use."
Hospital Variation, Cardiac Catheterization
The incidence of acute kidney injury significantly varied across hospitals, ranging from 10% to 32%, with the difference persisting even after multivariate adjustment.
"[T]his indicates that two patients with identical clinical characteristics would have an average increase of 26% in their risk of developing AKI simply due to being admitted to different hospitals," the authors wrote.
This observation looks to be evidence of a systems issue, Dr. Bonventre said.
"One could say that variations across hospitals could be related to the patients who are admitted to those hospitals," Dr. Bonventre said. "Perhaps a patient with a mild AMI might tend to be more likely to go to one community hospital, while someone with severe chest pain might be taken by ambulance to another hospital.
"Another possibility is it is not so much the initial patient management but the management of the contrast agents. Some hospitals may be more attentive to preventing AKI than other hospitals."
The magnitude of decline in AKI incidence was more pronounced in patients who had cardiac catheterization versus those treated conservatively. The crude incidence of acute kidney injury decreased from 24.6% in 2000 to 16.5% in 2008 among those who had that procedure.
"This could be related to the fact that there was more attention over the years to the amount or type of contrast agents that were given," Dr. Bonventre said. "Over time, if you reduce the contrast agent, you get fewer episodes of AKI."
The results of the study are intriguing, Dr. Okusa said. The data are clean, and the number of patients observed is large. Still, he would have liked to have seen more information on the treatment the patients received.
"There are data missing," Dr. Okusa said. "We don't necessarily know whether intravenous fluid was administered. We also don't know what type or volume of contrast they had. These are parameters where there is strong evidence that could affect outcomes in contrast-induced AKI. These are some of the limitations of this paper."
An invited commentary by Raymond K. Hsu, MD, and Chi-yuan Hsu, MD, MSc, of the Division of Nephrology at the University of California, San Francisco, noted the need for future work in this area (Arch Intern Med 2012;172:253–254).
"One, further population-based epidemiology studies should be conducted to better define contemporary AKI disease incidence—overall and in specific demographic, clinical, and geographic subgroups," the authors wrote.
"Two, if the incidence of AKI is increasing overall but falling in some subgroups (e.g., among patients with acute myocardial infarction), we need to understand what is driving up the AKI rate in other groups."
These differences must be examined, Dr. Bonventre agreed.
"One should take advantage of the systematic differences in the way that patients are managed across those different centers and come to the best practices," he said. "That should define subsequent studies."