The Mystery of Inappropriate Hypoxia After Single Lung Transplant

Abstract

<h3>Introduction</h3> Single lung transplantation (SLT) is a treatment option for end stage lung disease in select patients, increasing utilization of a scarce resource. Increase in relative perfusion to the allograft from hypoxic vasoconstriction typically ameliorates hypoxia despite native lung disease. We present a SLT recipient with idiopathic pulmonary fibrosis (IPF) who developed hypoxia due to inappropriate shunting to the native lung after an IPF exacerbation. <h3>Case Report</h3> A 66 year old female with IPF had a left SLT eight months prior to presentation. Four months post transplant, she developed submassive bilateral extensive pulmonary embolism (PE) requiring suction thrombectomy, catheter-directed thrombolysis and anticoagulation without subsequent oxygen requirement. Three months later, she presented with two weeks of productive cough and hypoxia requiring high flow nasal cannula. CT chest showed worsening native lung fibrosis with ground glass opacities without PE or allograft infiltrate. Bronchoalveolar lavage was negative for infection, recent transbronchial biopsies were negative for rejection, and no donor specific antibodies were identified. Despite empiric antibiotics and pulse dose steroids for native lung exacerbation, she developed worsening hypoxia with progressive native lung infiltrates. A perfusion scan revealed 68% and 32% perfusion to the left and right lung, respectively. A right heart catheterization was performed, showing no intracardiac or pulmonary shunt, a mildly increased gradient across the left pulmonary artery (PA) anastomosis, and a marked improvement in left PA PaO2 during right PA balloon occlusion. On hospital day 16, repeat perfusion scan demonstrated an increase in relative perfusion to the allograft (83%). The patient was discharged on 3L oxygen and remains stable as an outpatient. <h3>Summary</h3> Severe hypoxia in the setting of a functioning SLT during a native lung exacerbation is rare. Literature on normal perfusion after SLT remains limited, with small studies suggesting ∼75% of fractional perfusion to the allograft without native lung exacerbation. Similar cases of inappropriate shunting after SLT had improvement in oxygenation after contralateral PA banding with other options including intravascular interventions or contralateral SLT. Further studies characterizing optimal perfusion after SLT and interventions for inappropriate shunting are needed.