Among patients hospitalized with an acute myocardial infarction (AMI), about 20% will develop an acute kidney injury (AKI). This complication has been linked to adverse long-term outcomes, including permanent renal impairment and end-stage renal disease. Minor increases in serum creatinine levels have also been associated with increased mortality, longer hospitalizations, and higher costs. “Experts are increasingly emphasizing the importance of preventing AKI and promptly recognizing it in patients hospitalized with AMI,” says Mikhail N. Kosiborod, MD. “A better understanding of trends may help determine if recent prevention efforts have been successful. This data can also be used to form initiatives aimed at preventing AKI.”
Taking a Closer Look at AKI
In the February 13, 2012 Archives of Internal Medicine, Dr. Kosiborod and colleagues analyzed data from a registry of patients admitted to 56 hospitals across the United States to examine trends in AKI from 2000 to 2008. AKI was defined as an increase of at least 0.3 mg/dL in creatinine levels or a relative increase of at least 50% during hospitalization. “The database used in our analysis had an extensive collection of laboratory data, including detailed assessments of renal function,” says Dr. Kosiborod. “Using this information, we wanted to understand the incidence trends in AKI and use of AKI prevention strategies among patients hospitalized with AMI.”
According to findings, the incidence of AKI declined from 26.6% in 2000 to 19.7% in 2008 (Figure). In-hospital mortality also declined in patients who developed AKI, dropping from 19.9% in 2000 to 13.8% in 2008. This improvement occurred despite a concomitant increase in AKI risk factors, including chronic kidney disease, cardiogenic shock, diabetes, heart failure, coronary angiography, and PCI (Table). “This is overall a very positive message,” said Dr. Kosiborod. “It suggests that the efforts by cardiologists aimed at preventing AKI seem to be bearing fruit.”
Another key finding was that there was substantial variability in AKI rates across participating sites. “This suggests that hospital-based processes of care may, in part, contribute to AKI incidence,” Dr. Kosiborod says. “It highlights that we have a potential opportunity for quality improvement.”
Dr. Kosiborod’s study team gave careful consideration to adjusting for demographic variables (eg, age, race, ethnicity, and sex) and comorbidities (eg, presence of diabetes, heart failure, cardiogenic shock, and baseline renal function) that are known AKI risk factors, which strengthened the results. This ensured that trends were not simply due to variation in patient characteristics over time or to differences in vigilance of renal function monitoring. The results also remained unchanged when the authors looked at the temporal trends in severe AKI.
Encouraging AKI Prevention Efforts
It is difficult to determine if the declining rates of AKI reflect increased awareness and prevention efforts or better selection of patients for coronary angiography and PCI. Dr. Kosiborod believes that increased awareness and use of preventative strategies are playing a role. “It’s possible that greater emphasis on AKI prevention efforts in the clinical guidelines has impacted physician behavior,” he says. One example of this is greater use of N-acetylcysteine (NAC) over time that was observed in the study. “Although NAC is not an effective treatment for AKI prevention, it’s probably a surrogate for using other, more effective preventative strategies, such as pre-procedural hydration, limiting contrast volume, and avoiding nephrotoxic medications” Dr. Kosiborod says.
Despite the observed improvements, there are still many opportunities for quality improvement in AKI, according to Dr. Kosiborod. There was wide variation across hospitals in AKI incidence and in medications that might influence AKI. These variations may reflect differences in hospital-based processes of care. “By gaining a better understanding of the practice patterns at centers with low AKI rates, we can get valuable insights into effective strategies for AKI prevention,” Dr. Kosiborod says. “In turn, this information can then be used to implement interventions to decrease the burden of AKI across hospitals.”
Understanding Hospital Variations
More prospective studies are needed to better understand the reasons for the variations across hospitals that were observed in the analysis and to define opportunities for improving patient outcomes further. More population-based epidemiology studies to better define AKI incidence— overall and in specific demographic and clinical subgroups—are warranted. “If the incidence of AKI is decreasing overall but rising in some subgroups, then we need to understand what is driving these differences,” says Dr. Kosiborod. “In addition, developing better hospital-based strategies to predict and prevent AKI on the individual patient level is needed.”