*Purpose: Lung transplantation surgery increases the risk of pulmonary embolism (PE), with an incidence described between 6% to 27%, based on data from 15 years ago. It is unclear what impact, if any, the changes in pulmonary artery blood flow after single lung transplant have on the risk of pulmonary embolism. This study aims to determine the prevalence and laterality of pulmonary embolism in patients with a single lung transplant.

*Methods: A retrospective cohort study was conducted in a single lung transplant center. Patients who underwent single lung transplantation between January 1st, 2010 and September 20th, 2020, were included. Data on patient factors, presence of deep venous thrombosis (DVT), and presence of PE, diagnosed either with computed tomography or nuclear ventilation/perfusion (VQ) scan, were collected. An “intermediate probability” on VQ scan was considered a positive test. Patients undergoing repeat transplantations were only counted once, and those with evidence of thrombosis prior to transplant were excluded.

*Results: A total of 135 patients were evaluated, of which 2 were excluded given inadequate studies, and 2 were excluded due to the presence of thrombosis prior to transplantation. The median age at transplant was 68, and 48.9% of patients were female. 16.8% of patients identified as Hispanic and the average BMI was 25.9. The majority of patients had primary diagnosis of idiopathic pulmonary fibrosis (52.7%) or chronic obstructive pulmonary disease (32.1%). The median lung allocation score was 36.6. Forty-two patients underwent evaluation for PE, of which 28.6% of patients had a positive test. The median days from transplant to the detection of PE was 130 days. Of patients evaluated for DVT, 26.1% had a positive test. Two-thirds of patients with pulmonary embolism had emboli found on the same side as the transplant, and 25% of patients had PE occurring on the native side. 50% of patients with PE also had DVTs. 31.3% of patients with RSLT had PE, compared to 20% for LSLT, but this was not statistically significant (p=0.49). Logistic regression models did not reveal a statistically significant risk factor for PE when evaluating age, gender, BMI, or LAS. Chi-square analysis did not reveal an association between native lung pathology and diagnosis of PE.

*Conclusions: The incidence of PE and DVT is consistent with prior studies. The majority, but not all, patients with pulmonary embolism have clots detected on the side of the transplant. This would suggest that the physiology of the blood flow to the transplanted lung counteracts the possible increased risk of clot formation on the native side. Most pulmonary emboli occur within the first two years following lung transplantation.

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