SP215SEVERE ACUTE KIDNEY INJURY IN CARDIOVASCULAR SURGERY: THROMBOTIC MICROANGIOPATHY AS A DIFFERENTIAL DIAGNOSIS TO ISCHEMIC RENAL INJURY

Abstract

INTRODUCTION: Acute kidney injury (AKI) after cardiovascular surgery (CVS) is a serious complication associated with high morbidity and mortality. Following CVS AKI is presumed to be mainly secondary to renal ischemia as a result of reduced cardiac output and the implementation of extracorporeal circulation. However, recent evidence suggests that nephrotoxic agents, systemic inflammation and other factors might also play an important role. Thrombotic microangiopathies (TMA) are a rare complex of diseases characterized by a microangiopathic hemolytic anemia (MAHA), thrombocytopenia and organ dysfunction. Atypical hemolytic uremic syndrome (aHUS) is a type of TMA characterized by overactivation of the alternative complement pathway that clinically presents with AKI and/or other extrarenal manifestations such as central nervous systemabnormalities. Studies suggest a 2-step model in which the presence of predisposing factors and a triggering agent lead to overactivation of the complement system. The aim of this study was to assess the frequency of postoperative AKI in CVS patients and the impact of TMA episodes in the development of AKI. METHOD(S): We retrospectively analyzed patients who underwent AKI needing RRT upon CVS on the intensive care unit (ICU) of our hospital between the 11.2017 and 12.2018. RRT was initiated on patients with either refractory acid-base disturbances, lactic acidosis or oliguria/anuria. Renal function was assessed using eGFR as calculated with the CKD-EPI creatinine equation. Patients with post-surgery AKI with or without signs of neurological impairment, presenting with drowsiness or delayed awakening following anesthesia, and laboratory findings suggesting MAHA by Coombs-negative anemia and non-immune thrombocytopenia fulfilled diagnostic criteria for a TMA. After measuring ADAMTS13 activity and complement activity, patients were started on plasma exchange (PE) and/or eculizumab based on the clinical and laboratory evolution, as assessed by the nephrology department. RESULT(S): Among a total of 665 patients admitted between 11.2017 and 12.2018 to the CVS unit of our hospital, 60 patients needed RRT on the ICU post-surgery. 7 patients were on chronic hemodialysis before surgery (CKD Stage V). Out of the 53 (7,96%) patients with a new AKI needing RRT (RRT-AKI), 14 died (26,4%) and 12 (22,6%) did not recover renal function and were discharged on regular hemodialysis. Within the RRT-AKI group, 12 (22,6%) patients fulfilled TMA criteria. Further 3 patients presenting with AKI post-surgery met TMA criteria but did not require RRT. 10 out of 15 TMA patients were started on PE and/or eculizumab. Mean ADAMTS13 activity in these patients was 58%, excluding TTP as a differential diagnosis. Complement diagnostics revealed complement activation in 8 out of 15 patients. TMA was mainly associated with combined surgical procedures including aortic valve replacement and the use of extracorporeal circulation with hypothermia (9 out of 15). Among TMApatients requiring RRT (n = 12), 4 never recovered renal function and were discharged on hemodialysis. There were no deaths among patients with a TMA (p=0.0183). CONCLUSION(S): Our observations suggest that post-operative AKI in CVS patients is not only a result of ischemic injury. Diagnosis and adequate treatment of TMA in this patient group could reduce post-operative end stage chronic kidney disease and overall mortality. Further studies are needed to assess complement activation in CVS as a potential trigger for TMA.