Extracorporeal fetal support: a new animal model with preservation of the placenta.
Previous models of support for premature sheep fetuses have consisted of cesarean delivery followed by catheterization of umbilical or central vessels and support with extracorporeal membrane oxygenation (ECMO). The limitations of these models have been insufficient blood flow, significant fetal edema, and hemorrhage related to anticoagulation. We performed a gravid hysterectomy on 13 ewes between 135 and 145days gestational age. The uterine vessels were cannulated bilaterally and circulatory support was provided via ECMO. Successful transition was defined as maintenance of fetal heart rate for 30minutes after establishing full extracorporeal support. Circuit flow was titrated to maintain mixed venous oxygen saturation (SvO2) of 70-75%. Seven experiments were successfully transitioned to ECMO, with an average survival time of 2hours 9minutes. The longest recorded time from cannulation to death was 6hours 14minutes. By delivering a circuit flow of up to 2120ml/min, all but one of the transitioned uteri were maintained within the desired SvO2 range. We report a novel animal model of fetal ECMO support that preserves the placenta, mitigates the effects of heparin, and allows for increased circuit flow compared to prior techniques. This approach may provide insight into a technique for future studies of fetal physiology.