Severe Acute Kidney Injury in Cardiovascular Surgery: Thrombotic Microangiopathy as a Differential Diagnosis to Ischemia Reperfusion Injury. A Retrospective Study

[Thrombotic microangiopathies in surgical intensive care medicine with special consideration of atypical hemolytic uremic syndrome]

Thrombotic microangiopathies (TMA) are rare diseases, which are defined by the triad microangiopathic hemolytic anemia, thrombocytopenia and organ damage, and are associated with high morbidity and mortality. The recognition of a TMA and the distinction of important differential diagnoses are key factors, particularly in a perioperative context and in routine clinical intensive care. The further differentiation of the different TMA subtypes, such as thrombotic thrombocytopenic purpura (TTP), Shiga toxin-producing Escherichia coli hemolytic uremic syndrome (STEC-HUS) and atypical hemolytic uremic syndrome (aHUS), based on the underlying pathophysiology and the development of new targeted treatment options in recent years have significantly improved the prognosis. A close interdisciplinary cooperation between critical care specialists and specialist disciplines experienced in the treatment of TMA, is essential for a prompt diagnosis and the initiation of the appropriate treatment.

Postsurgical Thrombotic Microangiopathy and Deregulated Complement

Postsurgical thrombotic microangiopathy (TMA) is a complication associated with significant morbidity and mortality. Still, the pathophysiological underlying mechanism of postsurgical TMA, a diagnosis often overlooked in postoperative patients with acute kidney injury and thrombocytopenia, is largely unknown. Here, we report the case of a 56-year-old male that developed anuric acute kidney injury, Coombs-negative hemolysis, and thrombocytopenia after surgical aortic arch replacement. Massive ex vivo complement activation on the endothelium, a rare complement gene variant in C2, at-risk haplotype MCPggaac, and excellent response to therapeutic complement inhibition, points to the pivotal role of complement in the pathophysiology of disease. Moreover, the importance of a multidisciplinary team approach in (postsurgical) thrombocytopenia is emphasized.

Thrombotic microangiopathy following aortic surgery with hypothermic circulatory arrest: a single-centre experience of an underestimated cause of acute renal failure

OBJECTIVES

Acute kidney injury (AKI) following surgery involving the heart-lung-machine is associated with high mortality and morbidity. In addition to the known mechanisms, thrombotic microangiopathy (TMA) triggered by the dysregulation of complement activation was recently described as another pathophysiological pathway for AKI following aortic surgery. The aim of this retrospective study was to analyse incidence, predictors and outcome in these patients.

METHODS

Between January 2018 and September 2019, consecutive patients undergoing aortic surgery requiring hypothermic circulatory arrest were retrospectively reviewed. If suspected, diagnostic algorithm was initiated to identify a TMA and its risk factors, and postoperative outcome parameters were comparably investigated.

RESULTS

The incidence of TMA in the analysed cohort (n = 247) was 4.5%. Multivariable logistic regression indicated female gender {odds ratio (OR) 4.905 [95% confidence interval (CI) 1.234-19.495], P = 0.024} and aortic valve replacement [OR 8.886 (95% CI 1.030-76.660), P = 0.047] as independent predictors of TMA, while cardiopulmonary bypass, X-clamp and hypothermic circulatory arrest times showed no statistically significance. TMA resulted in postoperative AKI (82%), neurological disorders (73%) and thrombocytopaenia [31 (interquartile range 25-42) G/l], corresponding to the diagnostic criteria. Operative mortality and morbidity were equal to patients without postoperative TMA, despite a higher incidence of re-exploration for bleeding (27 vs 6%; P = 0.027). After 6 months, survival, laboratory parameters and need for dialysis were comparable between the groups.

CONCLUSIONS

TMA is a potential differential diagnosis for the cause of AKI following aortic surgery regardless of the hypothermic circulatory arrest time. Timely diagnosis and appropriate treatment resulted in a comparable outcome concerning mortality and renal function.