Gas exchange during perfluorocarbon liquid immersion: Life-support for the ex utero fetus

Abstract

Respiratory mortality and morbidity remain major consequences of extreme prematurity. Percutaneous transfer of oxygen and carbon dioxide is possible in the newborn human. Perfluorocarbon (PFC) liquids have excellent oxygen and carbon dioxide carrying capacity. Animals can breath immersed in perfluorocarbon liquids and maintain adequate gas exchange. Our hypothesis is that the combination of spontaneous tidal perfluorocarbon breathing and respiration through the skin immersed in perfluorocarbon will allow adequate gas exchange in the preterm newborn. In this pilot study we aimed to observe the effects of immersion in FC-77 perfluorocarbon liquid on the preterm lamb. PILOT DATA: Four preterm lambs at 100-115 days gestation were delivered using a modified EXIT procedure. Immediately after complete delivery, the catheterised lamb was immersed in warm, oxygenated FC-77 perfluorocarbon liquid. Physiological monitoring was done for up to 60 min. All lambs were warmed adequately and seemed to have centrally intact circulation initially. All had little or no respiratory effort and there was no appreciable lung expansion. All had severe respiratory acidosis. For the provision of immediate ex utero care to the 'fetus' there are three requirements: adequate gas exchange surfaces and sufficient oxygen and carbon dioxide gradients, a functioning circulation, and an environment capable of keeping the lamb warm (thus minimising metabolic demand, oxygen consumption and carbon dioxide production). In this pilot study the greatest initial problem was the severe and rapidly worsening respiratory acidosis. The major problem was a lack of respiratory drive. No lung expansion from the outset would yield zero contribution to gas exchange from the lungs. An intact central circulation does not necessarily mean that the pulmonary circulation, respiratory drive and/or the skin circulation are adequate. For adequate gas exchange to occur it will require a 'breathing' animal with expanded alveoli. If the transition from the normal in utero state to immersion in PFC was immediate, and lung expansion was achieved, it could still be possible to achieve adequate gas exchange through the skin and lungs of the extremely preterm newborn. Given the potential for gas exchange across the skin of the extremely preterm infant we hypothesise that the immersion of extremely preterm infants in PFC liquid will allow optimal percutaneous gas exchange to occur. Given some lung gas exchange with less injurious liquid ventilation (spontaneous or mechanical) we hypothesise that the combination of skin and lung gas exchange will provide sufficient gas exchange to support life.