Ultrasound Assessment of Pleural Effusions After Orthotopic Pig-to-Baboon Cardiac Xenotransplantation

Background: Pleural effusions develop frequently after cardiac surgery in humans. Lung ultrasound is an essential non-invasive tool in the diagnosis and treatment of these effusions. Pleural effusions also develop regularly after preclinical cardiac xenotransplantation experiments. Unlike in the human setting, modern ultrasound devices lack pre-installed tools for calculating the volume of pleural effusions in baboons. The aim of this study was to analyze ultrasound examinations of pleural effusions after orthotopic pig-to-baboon cardiac xenotransplantation experiments in order to develop a formula for calculating the effusion volume based on ultrasound measurements.

Methods: Hearts from seven genetically modified (GGTA1-KO, hCD46/hTBM transgenic) juvenile pigs were orthotopically transplanted into male baboons. Postoperatively, the baboons were tested regularly for the development of pleural effusions using ultrasound. When thoracocentesis was required, the drained effusion volume (EV) was compared to ultrasound-derived calculations using various formulas. These calculations were based on measuring the distance between lung and diaphragm at the effusions' maximum height (H_max). Subsequently, the most promising formula was used to describe the interobserver variability between trained and untrained staff members to predict effusion volumes based on ultrasound measurements.

Results: Ultrasound measurement correlated very strongly with the absolute EV (r = 0.9156, p < 0.0001), with EV indexed to total body weight (r = 0.9344, p < 0.0001) and with EV indexed to body surface area (BSA) (r = 0.9394, p < 0.0001). The ratio between H_max and EV increased with total body weight and BSA and also depended on the baboon species. The sonographic measurements taken by an experienced and an inexperienced observer showed only low interobserver variability. A Bland-Altman plot of both observers' measurements showed an overall bias of -2.39%.

Conclusion: Ultrasound imaging provides a simple and non-invasive tool for measuring pleural effusion quantity in baboons. This facilitates simple and efficient monitoring even in the hands of untrained personnel and may guide the decision-making to perform thoracocentesis.