Clinical cause of presumed acute tubular necrosis requiring renal replacement therapy and outcome of critically ill patients: post hoc analysis of a prospective 7-year cohort study

Acute kidney injury (AKI) secondary to acute tubular necrosis (ATN) is common in critically ill patients, and causes significant morbidity and mortality. The underlying etiology of ATN can be divided into pure ischemic, pure nephrotoxic, and mixed causes. This post-hoc analysis of a prospective cohort study aimed to investigate whether the cause (pure vs. mixed) of ATN affects the short- and long-term outcome of critically-ill patients.

A total of 425 critically-ill patients with AKI secondary to clinically diagnosed ATN were divided into three groups according to the cause of ATN. Of these patients, 215 had mixed ATN, 203 had pure ischemic ATN, and seven had pure nephrotoxic ATN. All patients had one episode of AKI only. No patient had pre-existing chronic kidney disease. Patients were followed throughout their hospital stay (mortality rate, recovery of renal function at discharge) and up to 7 years thereafter.

The three patient groups differed in their demographic and clinical characteristics. The in-hospital mortality rates were 55% in the presumably mixed-cause ATN group, 39% in the pure ischemic group, and 29% in the pure nephrotoxic group. Complete renal recovery at discharge was documented in five out of five surviving patients with nephrotoxic ATN (100%) and in 92 out of 124 surviving patients with pure ischemic ATN (74%), but only in 29 out of 97 patients with mixed ATN (30%). None of the surviving patients was lost during the 7-year follow-up. At the end of the observation period, 60% of the survivors of pure ATN, compared with 22% of the survivors of mixed ATN, were alive. After 7 years, 6% of the living patients with pure ATN had mild-to-moderate chronic kidney disease, whereas 38% of the mixed group patients had advanced CKD or end-stage renal disease.

The cause of presumed ATN has a profound impact on short- as well as long-term outcomes of critically-ill patients with AKI requiring renal replacement therapy. The challenge for intensivists is to avoid further injury to the kidneys of these patients.