Umbilical cannulation optimizes circuit flows in premature lambs supported by the EXTra-uterine Environment for Neonatal Development (EXTEND)

Abstract

EXTEND (EXTra-uterine Environment for Neonatal Development) is a novel system that promotes physiologic development by maintaining the premature lamb in a sterile fluid environment and providing gas exchange via a pumpless arteriovenous oxygenator circuit. During the development of EXTEND, different cannulation strategies evolved with the aim to improve circuit flow. This study examines how different cannulation strategies affect EXTEND circuit hemodynamics in extreme premature lambs. 17 premature lambs were cannulated at gestational ages 105–117 days (term 145–150 days) and supported on EXTEND for up to 4 weeks. Experimental groups were distinguished by cannulation strategy: carotid artery outflow and jugular vein inflow (CA/JV, n = 4); carotid artery outflow and umbilical vein inflow (CA/UV, n = 5); double umbilical artery outflow and umbilical vein inflow (UA/UV, n = 8). Circuit flows and pressures were measured continuously. As we transitioned from CA/JV to CA/UV to UA/UV cannulation, mean duration of circuit run and weight-adjusted circuit flows increased (P < 0.001) and frequency of flow interruptions declined (P < 0.05). Umbilical vessels generally accommodated larger-bore cannulas, and cannula caliber was directly correlated with circuit pressures and indirectly correlated with flow:pressure ratio (a measure of post-membrane resistance). We conclude that UA/UV cannulation in fetal lambs on EXTEND optimizes circuit flow dynamics and flow stability, and supports circuit flows that closely approximate normal placental flow.

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