Extracorporeal Membrane Oxygenation and Renal Function

Extracorporeal Membrane Oxygenation

Extracorporeal membrane oxygenation (ECMO) is intended to provide temporary extracorporeal respiratory support by the use of an artificial membrane lung in case of pulmonary failure unresponsive to conventional treatments. ECMO is indicated in case of high mortality risk, provided the underlying pathology is potentially reversible. Indeed, ECMO provides a life support system that enables evaluation, diagnosis, and, possibly, resolution of the most severe acute lung diseases. Although the technique was intended originally to buy time for the lungs to heal, ECMO is now recognized as a powerful tool to allow lung rest and foster recovery by minimizing the invasiveness of mechanical ventilation. In patients with respiratory failure, the common approach is the venovenous VV-ECMO bypass in contrast with the venoarterial VA bypass, which is used in the presence of severe heart failure. Impaired renal function is frequent in all conditions requiring ECMO, and ECMO can affect the renal system. Physiologic, clinical, and technical aspects of VV- and VA-ECMO treatments are described in dedicated chapters of this book. Here, we discuss the effects of VV-ECMO on renal function in adult patients, focusing on the incidence and pathophysiology of renal failure in ECMO patients. A brief description of the techniques available for combined ECMO and renal replacement therapy also is included.

Acute Kidney Injury in Extracorporeal Membrane Oxygenation Patients

Acute kidney injury (AKI) identifies a rapid deterioration of kidney function, characterized by reduced glomerular filtration rate (GFR) and urine output yielding increased serum creatinine. The definition of AKI evolved over the years and recently the KDIGO (Kidney Disease: Improving Global Outcomes) task force revisited the original RIFLE (risk, injury, failure, loss of kidney function, and end-stage kidney disease) and AKIN (Acute Kidney Injury Network) criteria. All the definitions are based on clinical and physiologic markers (e.g., serum creatinine, electrolytes, and urea nitrogen plus urine output), and the RIFLE and the AKIN criteria, from which the KDIGO definition derived, have been validated in various patient populations including ECMO and showed high sensitivity and specificity and a good capacity to predict clinical outcomes. However, current physiologic markers for AKI (elevated serum creatinine and decreased urine output) are not adequate for early diagnosis, because their changes occur late and often are influenced by many other factors (e.g., serum creatinine increases only when GFR declines more than 50%) and, for this reason, other markers are under investigation. Among the other candidates, one of the most sensitive appears to be the neutrophil gelatinase-associated lipocalin (NGAL), but, up to now, neither NGAL nor any of the others proposed biomarkers has replaced serum creatinine (SCr) in AKI definition.

AKI is a common complication in critically ill patients treated with extracorporeal lung support, and it may be associated with worse outcomes. The Extracorporeal Life Support Organization (ELSO) registry defined renal complications in ECMO patients by serum creatinine values between 1.5 and 3 mg/dL or higher and/or the need for dialysis. The ELSO reported in 2012 that, among adult patients supported by VV-ECMO for severe respiratory failure, SCr elevation between 1.5 and 3 mg/dL occurred in 18.9% of the cases (survival 37%), whereas in 12.9% of the cases SCr exceeded 3 mg/dL (survival 39%); dialysis was used in 14.2% (survival 39%), hemofiltration in 23.3% (survival 51%) and, finally, continuous arteriovenous hemodialysis (CAVHD) in 12.5% cases (41% survival). Studies using AKIN and RIFLE definitions reported an incidence of renal failure in adult patients with respiratory failure ranging between 34% and 78% with resulting mortality up to 80%. Lin et al. reported 78% mortality in patients with AKI versus 20% in non-AKI patients treated with ECMO. Kielstein et al. reported an 87% mortality rate in ARDS patients with AKI requiring RRT treated with ECMO. The use of renal replacement therapy (RRT) in adult patients in published ECMO series ranges between 25% and 68%. Zangrillo et al. reported that renal failure requiring continuous hemofiltration occurred in 52% of the patients treated with ECMO, ranking among the most common complications. Haneya et al., in a retrospective observational study in 262 adult patients with ARDS treated with VV-ECMO, found that 50% of the patients required RRT for renal failure or fluid overload (FO) . The need for RRT in patients receiving ECMO support is associated with increased mortality. In ECMO patients, the need for RRT may reflect inadequate renal perfusion or direct injury to the kidney either because of the disease process itself or to ECMO-associated side effects (e.g., hemolysis, multiple transfusion). Evidence of fluid overload (FO) usually plays a key role in the decision to start RRT in ARDS treated with ECMO, and it is a factor associated with longer ECMO duration and higher mortality. In fact, according to an online survey regarding renal support therapy during ECMO based on 65 international ECMO centers, the predominant indication for RRT was the treatment (43%) or prevention (16%) of FO. Haneya et al. reported that FO was the indication for RRT in 66% of their cohort of ECMO patients and that early RRT application for FO prevention improved the outcome and did not seem to affect mortality.