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ORIGINAL ARTICLE

Tolerance of placenta to normothermic umbilical circulatory arrest

Renato S AssadI; Fan-Yen LeeII; Joseph SabikI; Saralyn MackenzieII; Frank L HanleyII

DOI: 10.1590/S0102-76381992000300001

ABSTRACT

Elevation of placental vascular resistance (PVR) and depression of fetal gas exchange occurs after fetal cardiopulmonary bypass (CPB). Excluding the placenta from the CPB circuit may protect the placental vasculature from the unwanted stimuli which lead to elevated PVR. To evaluate this approach, 9 isolated in-situ sheep placentas were placed on CPB by cannulating the umbilical vessels, with a mean umbilical artery flow of 214 ml/min/kg. After 30 minutes of stable flow, placental circulation was arrested for 30 minutes, simulating the umbilical vessel clamp time during whole body fetal CPB. Placental circulation was then restored to baseline values. Placental gas exchange and maternal placental blood flow were evaluated before and after arrest. Interruption of blood flow to the placenta for 30 minutes under normothermic conditions does not affect placental function or maternal placental blood flow. It may be possible to exclude the placenta from the circulation during fetal CPB as a mean of eliminating the detrimental effects of CPB on placental gas exchange. This model suggests an alternative way of designing a scheme for clinical fetal CPB which may avoid the negatives effects of CPB on the placenta.

RESUMO

O aumento da resistência vascular placentáriae distúrbios de trocas gasosas freqüentemente ocorrem após a circulação extracorpórea (CEC) fetal. A utilização de um circuito convencional de CEC que exclua a placenta da circulação através do clampeamento temporário do cordão umbilical pode proteger a vasculatura placentária dos estímulos que levam ao aumento da resistência vascular. Para avaliar a tolerância placentária à parada normotérmica do fluxo sangüíneo umbílico-placentário, 9 placentas de ovelhas isoladas in-situ, foram colocadas em CEC através da canulação dos vasos umbilicais, com fluxo médio de artéria umbilical de 214 ml/min/kg. Após 30 minutos de estabelecimento da CEC, a circulação placentária foi interrompida por 30 minutos, simulando o clapeamento do cordão umbilical durante a CEC fetal total. Posteriormente, a circulação placentária foi restabelecida aos valores basais. A troca de gases placentária, o fluxo sangüíneo e a resistência vascular materno-placentários foram avaliados antes e depois da parada circulatória. Não houve diferença estatisticamente significante entre os gradientes transplacentários de pO2 e pCO2, indicando que a interrupção do fluxo sangüíneo placentário por 30 minutos, em condições normotérmicas, não afeta a função placentária. Este modelo sugere um método alternativo para a aplicação clínica da CEC fetal, através da exclusão da circulação umbílico-placentária durante a CEC fetal, eliminandose, assim, os efeitos deletérios da CEC nas trocas gasosas placentárias.
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