Evaluation of Gas Exchange and Hemocompatibility of an Experimental Oxygenator at Anticipated Human Fetal Flow Rates in Fetal Lambs Using a Dual Oxygenator Platform in the EXTra-Uterine Environment for Neonatal Development (EXTEND) System.

Background: We previously reported the EXTEND (EXTra-uterine Environment for Neonatal Development) system provides physiologic support of fetal lambs (105-111 days gestational age; GA) via a pumpless arteriovenous circuit using a commercially available oxygenator (Maquet-Ox). However, for anticipated human subjects at 23-28 weeks of GA, a smaller oxygenator is required. To meet this requirement, a proprietary oxygenator (Experimental Oxygenator: Exp-Ox) was developed.

Methods: Fourteen lambs (mean GA 99 days, mean weight at cannulation 1.36 kg) were placed on the EXTEND system. Thereafter, Exp-Ox was connected in parallel with the Maquet-Ox, and its durability and hemocompatibility were assessed over a prolonged use of up to 21 days, utilizing a dual oxygenator platform. Blood flow to Exp-Ox was increased over time using a tubing clamp to maintain the anticipated human fetal flow rates (50-165 mL/min).

Results: Throughout the study, there was no deterioration in the oxygen and CO₂ exchange function. The pressure drop in the Exp-Ox remained unchanged over time, with no statistically significant difference, whereas the calculated Exp-Ox resistance (pressure drop/blood flow) decreased since the change in pressure drop increased at a slower rate than the increase in blood flow. The quantitative clot burden in the Exp-Ox following completion of the study ranged from 0.03% to 2.55%, with no correlation to study duration.

Conclusions: The study demonstrated the Exp-Ox maintained its ability to transfer oxygen and CO2 and sustained hemocompatibility for up to 21 days at anticipated fetal flow rates on the EXTEND system.