RESUMEN
BACKGROUND: The extrauterine fetal incubation system must meet stable blood gas exchange and sufficient oxygen supply to provide the physiologic oxygen consumption of the fetus. In the fetus, blood gas exchange is totally sustained by the placental circulation. The placenta can be regarded as an extracorporeal organ, and the basic structure of placental circulation comprises arteriovenous (AV) bypass. To mimic this mode of circulation, we used AV ECMO (extracorporeal membrane oxygenation) in the goat fetus, and attempted to achieve stable blood gas exchange and oxygen supply to the fetus. METHODS: Pregnant goats, weighting 30 - 35 kg, were anesthetized with N2O-O2-enflurane. We performed a cesarean section with a midline incision, and cannulated via the umbilical vessels after a hysterotomy, and connected the fetuses to an ECMO circuit. The fetus was transferred to an incubator containing normal saline mixed with antibiotics. Blood samples were obtained every 4 to 6 hours from the circuit for electrolytes, hemoglobin and blood gas analysis and arterial blood pressure and heart rate were monitored through the umbilical artery. Oxygen delivery and consumption were calculated from the measured parameters. Microscopic examinations of the liver, kidney and lung were performed 24 hours after ECMO to know the effect of AV ECMO on the circulation of the organ. RESULTS: AV ECMO was done for 24 hours in the six goat fetuses and the main cause of death was circulatory failure. Heart rates and blood pressure were stable during ECMO. Sodium bicarbonate was injected when mild acidosis occurred and blood gas exchange was maintained stable. Mean pump flow rate was 156 +/- 62 ml/min/kg and oxygen extraction ratio was 30.4%. The liver function tests were sustained within normal limits both before and 24 hours after ECMO, but BUN and creatininincreased beyond upper normal limits 24 hours after ECMO. Microscopic features of the liver and kidney showed congestion 24 hours after ECMO. The fetal lung after 24 hours of ECMO especially showed an increase of mature capillaries in the septum and wall of alveoli compared with the twin fetal lung. CONCLUSIONS: These results indicate that the extrauterine fetal incubation model used for this study was suitable to blood gas exchange and utility of oxygen for goat fetuses.