Kidney Injury After Heart Surgery – A Japan National Center Biobank Network Investigation

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Sudden injury to the kidneys or acute kidney injury (AKI) in which waste excretion into urine is impaired can occur as a result of a multitude of shocks to the body including sepsis and cardiac surgery. The presence of AKI can be determined by measuring the small molecule metabolite creatinine in the blood. It is a break-down product of high energy phosphocreatine and is normally excreted by the kidney. A build-up of creatinine in the blood can therefore indicate kidney injury. AKI that persists for seven days or more is described as acute kidney disease (AKD).

AKI after cardiac surgery has a complex etiology that can vary person to person and has been well studied. The clinical course of AKD following cardiac surgery has been less well characterized. Eisei Noiri of the National Center Biobank Network, National Center for Global Health and Medicine, Tokyo, Japan, and colleagues therefore investigated the clinical course

of AKD after cardiac surgery, including its association with AKI, 90-day mortality, renal prognosis at hospital discharge, and long-term renal prognosis using a database including intensive care units (ICUs) at 18 hospitals. The results were published in the journal Scientific Reports.

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There were 3,605 patients eligible for the study. Progression to AKD was judged to occur in 11% of the study participants and was associated with non-elective (emergency) surgery. AKD was significantly associated with 90-day mortality after cardiac surgery, occuring in 20% of these patients. The 90-day mortality rates were 0.4%, and 2%, in the no injury and AKI groups, respectively.

The follow-up by a Nephrologist of patients with AKI is recommended in clinical practice guidelines for AKI because of their risk of progression to CKD. However, only a minority of AKI

patients actually receive a nephrologist follow-up in real-world practice due to patient volume and time constraints. Predicting which AKI patients will develop into AKD would help to ensure that AKI patients in greatest need were followed-up.

It is possible the study was confounded by various factors. Data was not collected on perioperative nephrotoxic agents, such as imaging contrast agents, which may have an effect on AKI. The diagnosis of AKD was based on creatinine alone, urine output volume was not considered for practical reasons.

“AKD after cardiac surgery was associated with 90-day mortality, 90-day renal prognosis, and 2-year follow-up, suggesting that this particular clinical condition may call for closer attention,” concluded the authors.