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Fetal cardiac surgery: hemodynamic characteristics of placenta during extracorporeal circulation

Renato S Assad; Fan-Yen Lee; Kim Berger; Frank I Hanley

DOI: 10.1590/S0102-76381991000100007


Decreased placental perfusion and respiratory gas exchange have been observed following experimental fetal cardiopulmonary bypass (CPB). To better characterize placental hemodynamics during CPB, 7 isolated in-situ lamb placentas were placed on a CPB circuit, using umbilical arterial and venous cannulation. Measures were taken to simulate normal placental hemodynamics. Perfusion flow rates were varied randomly from 15 to 300 ml/min/kg fetal wt. during both normothermia and hypothermia. Placental vascular resistance (PVR) remained constant when perfusion pressure and flow were varied above 40 mmHg and 150 ml/min/kg respectively. Below these values, PVR varied inversely. This increase in PVR was more marked when CPB was performed with hypothermia as compared to normothermia. The clinical implications is that decreased placental flow and pressure on CPB may lead to a vicious cycle resulting in further impariment of placental perfusion and respiratory gas exchange. Hypothermia promotes this impairment.


A diminuição da perfusão placentária com conseqüente distúrbio de trocas gasosas ocorre com freqüência após a circulação extracorpórea (CEC) fetal experimental. Com o objetivo de caracterizar a hemodinâmica placentária durante a CEC, foram colocadas em CEC sete placentas de ovelhas, isoladas in situ, através da canulação dos vasos umbilicais. O fluxo da CEC foi alterado de 15 a 300 ml/min/kg de peso fetal, em normotermia e hipotermia. A resistência vascular placentária (RVP) permaneceu constante durante uma pressão de perfusão e fluxo da CEC acima de 40 mmHg e 150 ml/min/kg, respectivamente. Abaixo destes valores, a relação da RVP com estes dois parâmetros foi inversamente proporcional. Um maior aumento da RVP foi observado durante a hipotermia. A implicação clínica destes achados reside no fato de que a diminuição do fluxo e da pressão de perfusão placentária durante a CEC pode conduzir a um ciclo vicioso, resultando em prejuízo adicional da perfusão placentária das trocas gasosas, sendo que a hipotermia agrava ainda mais esta disfunção placentária.
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