Post-Surgical Maintenance of Cardiac Function in an Ex Vivo Premature Lamb Model

INTRODUCTION: Ex vivo uterine environment (EVE) therapy is an experimental neonatal intensive care model for extremely preterm infants who, due to their extreme prematurity, are unable to survive on mechanical ventilation. EVE therapy involves surgical cannulation and ligation of umbilical vessels to connect parallel membranous oxygenators for fetal gas exchange, obviating the need to ventilate the extremely immature preterm lung. The aim of the current study was to evaluate the impact of the cannulation on fetal circulation and cardiac function using ultrasound measurements. METHODS: The study was performed on preterm lambs at gestational age (GA) of 115±3 days. Fetuses received either 8 Fr arterial and 10 Fr venous catheters (n=5, Group A) or 10 Fr arterial 10 Fr venous catheters n=5, Group B), which were placed into umbilical vessels. Fetal circulation (flow direction of ductus arteriosus; DA and foramen ovale; FO) and cardiac function (early and late diastolic filling ratio of mitral valve and tricuspid valve; MV-E/A and TV-E/A, left myocardial performance index; MPI, maximum systolic velocity of descending aorta; Ao-Vmax, and pre-load index of inferior vena cava; PLI) were measured immediately after surgery. Identical fetal measurements were performed using control (non-surgery) ewes of corresponding GA (n=6, Group C). The data were analyzed using the one-way analysis of variance (ANOVA) and Tukey honestly significant difference (HSD) test. RESULTS: Blood flow at DA and FO was maintained in a right to left direction in all groups. Regarding MV-E/A and TV-E/A, Group A had a significantly higher value than Group B or C. There was no significant difference between Group B and C. For MPI and Ao-Vmax, both Groups A and B were significantly different from C, and there was no significant difference between Group A and B. No difference was observed for PLI among the three groups. CONCLUSION: Fetal circulation was maintained immediately after surgery in both catheter groups. Enlargement of catheter diameter contributes to improvement in cardiac function as a result of decreasing in afterload. However, further improvement is necessary to eliminate differences in cardiac function between Control Group lambs and those treated with EVE therapy