Acute kidney injury (AKI) is a frequent occurrence in hospitalized patients and its overall incidence appears to be increasing. In addition, the number of patients in whom AKI is preceded by exposure to iodinated contrast is also increasing (see Figure 1). Patients who develop AKI in hospital are typically those undergoing major surgical procedures and individuals suffering from hemodynamic insults, such as gastrointestinal bleeding, myocardial infarction, or sepsis. AKI also occurs in outpatients, where the etiology is more likely to be caused by nephrotoxins such as contrast media administered during coronary angiography and contrast-enhanced CT exams. For both inpatients and outpatients with AKI, regardless of etiology, there is a strong association between the occurrence of AKI and adverse events.1 These adverse events include increased length of hospital stay, greater hospital costs and in-hospital mortality, increased cardiovascular events, progression to end-stage kidney disease, and increased mortality at one year.
The association between AKI and adverse outcomes has been found across diverse cohorts of patients and etiologies of AKI.1 Despite this consistent association, it remains unclear whether the kidney injury itself is the cause of the subsequent adverse events. This is particularly relevant when discussing the relationship between AKI and events that occur months to years after the episode that produced the AKI. It could be argued that there is something about the patients who develop AKI that predisposes them to these longterm adverse events. For example, patients who have a significant burden of cardiovascular risk factors (e.g. those with diabetes and hypertension) are more likely to suffer AKI following a hemodynamic insult and independently to have a higher risk for long-term cardiovascular events such as stroke or myocardial infarction, and even death. In such patients, AKI may be a ├óÔé¼´åİmarker™ of cardiovascular risk factor burden. Alternatively, AKI may in some direct way accelerate the atherosclerotic process, increasing the likelihood of a future stroke, acute myocardial infarction, or death. In these patients, AKI may be a cause of the later adverse events. Distinguishing between these two possibilities is not easy. However, the impact of these two possible explanations is vastly different.
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