RESUMEN
BACKGROUND: We examined potential maternal-fetal interactions during fetal cardiopulmonary bypass. these interactions, not previously described, may significantly influence attempts at fetal cardiac surgery. METHODS: Eight fetal sheep underwent cardiopulmonary bypass (5 singletons, 3 twins; 100-109 days) for 60 minutes using a centrifugal microcircuit (20 mL prime), and the placenta as oxygenator. We measured maternal hemodynamics, arterial blood gases, and changes in blood flow to the gravid uterus using bilateral uterine artery flow probes. Maternal measurements were correlated to fetal hemodynamics, blood gases, and umbilical blood flows. After bypass, fetuses were followed for 60 minutes. RESULTS: Decreases in uterine blood flow occurred without changes in maternal hemodynamics or arterial blood gases, but were associated with worsening fetal arterial blood gases (pH decreased from 7.2 +/- 0.2 to 7.0 +/- 0.1, partial pressure of carbon dioxide increased 45.6% and partial pressure of oxygen decreased 15.4%). Changes in maternal hemodynamics (decreased systolic blood pressure [17.5%, SD = 11] and decreased diastolic blood pressure [20.3%, SD = 15]) were only noted when uterine blood flows decreased by greater than 38.2% (SD = 26). Correction of maternal hypocalcemia (0.89 g/dL, SD = 0.1) led to improved uterine artery flows (28.3% increase, SD = 30). Finally, fetal sternotomy, cannulation, and cardiopulmonary bypass each decreased uterine artery flows by 27.5% (SD = 18), 31.0% (SD = 26), and 39.7% (SD = 25), respectively. Similar changes were not observed in the nonbypass twin. CONCLUSIONS: Significant changes in uterine blood flow can occur during fetal cardiopulmonary bypass support without apparent changes in maternal hemodynamics or arterial blood gases. These changes imply a unique transplacental maternal-fetal interaction. Limited data from the twin fetus suggest a localized mechanism involving only the segment of placenta exposed to extracorporeal circulation.
Asunto(s)
Puente Cardiopulmonar , Sangre Fetal/química , Feto/cirugía , Hemodinámica , Placenta/irrigación sanguínea , Útero/irrigación sanguínea , Animales , Velocidad del Flujo Sanguíneo , Presión Sanguínea , Dióxido de Carbono/sangre , Puente Cardiopulmonar/efectos adversos , Cateterismo , Femenino , Feto/patología , Edad Gestacional , Tamaño de la Camada , Intercambio Materno-Fetal , Oxígeno/sangre , Presión Parcial , Placenta/patología , Embarazo , Ovinos , Esternón/cirugíaRESUMEN
Fetal bypass presents several perfusion challenges, including the need for high arterial flow rates using flexible arterial and small venous cannulae. We hypothesized that vacuum-assisted venous drainage (VAVD) would improve drainage and allow perfusion at higher flow rates which are thought to prevent placental dysfunction induced by fetal bypass. We conducted bypass for 60 minutes in 14 fetal lambs (90-105 days gestation; approximately 1-1.5 kg) using a roller pump and various angled venous cannulae (8-12 Fr). VAVD at -20 mm Hg or -40 mm Hg was compared with gravity drainage. Average flow using gravity drainage was 139 ml/kg/min; after VAVD, we achieved average flows of 285 ml/kg/min (range, 109-481 ml/kg/min). VAVD at -40 mm Hg caused right atrial trauma in four fetuses; no injury was seen at -20 mm Hg. Venous air entrainment during repair of the injuries did not result in any apparent air embolism. Spontaneous pulmonary hemorrhage occurred in two fetuses at the highest flows (> or = 400 ml/kg/min). In all but one case, termination of bypass was followed by placental dysfunction within 120 minutes. VAVD can be safely applied during fetal bypass provided pressures are kept < or = -20 mm Hg. However, the achieved higher flow rates do not prevent postbypass placental dysfunction and may indeed be detrimental to the fetus.