Understanding Severe Hyperammonemia in Lung Transplantation

Purpose Elevated serum ammonia (NH3) level is often observed following lung transplantation. Idiopathic hyperammonemia syndrome (IHS), which is diagnosed as serum ammonia level over 200 umol/L on at least 1 occasion, is a rare, often fatal complication following lung transplantation. In this study, we analyzed the patients with hyperammonemia to understand the clinical manifestation of them. Methods 283 patients who underwent lung transplantation from January 2013 to June 2020 were retrospectively reviewed. We defined non-severe hyperammonemia as serum ammonia >38umol/L and severe hyperammonemia as >75umol/L. Results Elevated ammonia level was detected in 134 patients on median postoperative 10.4 days. 96 (86.6%) showed non-severe hyperammonemia. 38 (13.4%) developed severe hyperammonemia and among them, 5 (1.8%) suffered IHS. Baseline demographics were not significantly different between two groups. The amount of estimated blood loss (p=0.014) and intraoperative transfusion (p=0.037) was greater in the severe group. More patients in the severe group suffered acute rejection (15.8% vs 3.12%, p=0.016), postoperative bleeding (29.0% vs 11.5%, p=0.027), postoperative acute kidney injury (36.8% vs 17.7%, p=0.032), operative mortality (15.8% vs 1.0%, p=0.002), and overall mortality (55.3% vs 29.2%, p=0.002). Logistic regression analysis demonstrated that underlying chronic renal disease (OR4.5, p=0.008), pretransplant hospital stay (OR2.3, p=0.034), postoperative bleeding (OR2.4, p=0.037), acute rejection (OR5.4, p=0.013), as significant risk factors for severe hyperammonemia. Kaplan-Meier curves showed different survival rate of severe hyperammonemia patients from patients without hyperammonemia or non-severe hyperammonemia (figure 1). Conclusion Patients with severe hyperammonemia demonstrated discriminating clinical features from the non-severe group. Identifying high risk patients and applying aggressive treatment strategy might be helpful to overcome the outcome of lethal IHS.