Introduction: Pleural and cardiac effusions develop after cardiac allotransplantation and are treated with thoracic drains. After preclinical cardiac xenotransplantation experiments, however, drains must be removed already before extubation due to animal noncompliance. Consequently, if acute and chronic pleural effusions occurred they were evacuated by ultrasound guided thoracentesis. The aim of the study was to estimate the amount of effusion using ultrasound techniques and to differentiate exsudate (usually indicating inflammation) from transudate (typical for heart failure).

Methods: Orthotopic pig-to-baboon cardiac xenotransplantation experiments (n=15) were performed with genetically multi-modified pigs (GGTA1KO, hCD46, hTHBD) serving as organ donors. The immunosuppressive regime included mycophenolate mofetil, costimulation blockade and corticosteroids. Regular sonographic examinations were done in sedation; if thoracentesis was necessary, the size of the effusion was estimated by measuring the distance between lung and mid-diaphragm (LZ) in ultrasound images. The LZ was then correlated to the exact amount of aspirate using linear regression analysis (n=8). Effusion and blood samples were sent to the laboratory and were chemically processed (n=10). Using the shortened Light’s criteria, based on the effusion/serum ratio of protein and LDH, exsudates were differentiated from transudates. Additionally, levels of troponin T, NT-proBNP and IL6 were measured in both serum and effusion.

Results: The ultrasound measurements of LZ correlated well with the actual amount of aspirate (r=0.8279, p<0.0001). Regression analysis yielded the formula: VolPE=7.4×LZ+39. Five animals had exclusively exsudates, four animals had both forms of pleural effusions. In all cases, levels of troponin T, NT-proBNP and IL6 were higher in pleural effusions as compared to blood serum measurements. One animal (baboon 17492) had separate pericardial and pleural effusions. In this case the pleural effusions were exclusively transudates; troponin T levels were highest in the pericardial effusions, whereas IL6 levels were higher both in the pericardial and pleural effusions as compared to serum.

Conclusion: Pleural effusions in baboons can be estimated by 2D ultrasound. As the pleural and pericardial cavities were broadly connected after transplantation, the origin of the effusions is unclear; however, the results from baboon 17492 point towards pericardium due to highly elevated troponin. Cardiac failure was the most probable cause for ongoing transudates, infections and inflammation for exsudates.