Ventilation before Umbilical Cord Clamping Improves the Physiological Transition at Birth

Abstract

The transition from a fetus to a neonate at birth represents a critical phase in our life. Most infants make this transition without complications, but preterm infants usually require some form of assistance due to immature cardiopulmonary systems that predispose them to lifelong sequelae. As the incidence of preterm birth is increasing, there is now an urgent need for the development of management strategies that facilitate this transition, which will likely include improved strategies for the management of the maternal third stage of labor. For instance, recent studies on the physiological transition at birth have led to the discovery that establishing ventilation in the infant before the umbilical cord is clamped greatly stabilizes the cardiovascular transition at birth. While most benefits of delayed clamping previously have been attributed to an increase in placenta to infant blood transfusion, clearly there are other significant benefits for the infant, which are not well understood. Nevertheless, if ventilation can be established before cord clamping in a preterm infant, the large adverse changes in cardiac function that normally accompanies umbilical cord clamping can be avoided. As preterm infants have an immature cerebral vascular bed, large swings in cardiovascular function places them at high risk of cerebral vascular rupture and the associated increased risk of mortality and morbidity. In view of the impact that cord clamping has on the cardiovascular transition at birth, it is also time to re-examine some of the strategies used in the management of the third stage of labor. These include the appropriate timing of uterotonic administration in relation to delivery of the infant and placenta. As there is a lack of evidence on the effects these individual practices have on the infant, there is a necessity to improve our understanding of their impact in order to develop strategies that facilitate the transition to newborn life.

Keywords: delayed cord clamping; neonatal; preterm birth; transition; umbilical cord clamping.

Figures

Figure 1

Left Panel: The fetal circulation is unique due to the presence of the placenta, which provides the gas-exchange requirements of the fetus. The lungs are filled with fluid and, as a result, pulmonary vascular resistance (PVR) is high and the majority right ventricular output bypasses the pulmonary circulation through the ductus arteriosus (DA). Therefore, the placenta supplies both left and right ventricular output, with left ventricular output being support by blood flow through the foramen ovale (FO). Middle Panel: With clamping of the umbilical cord you immediately remove placental supply of right and left ventricular output, resulting in an instantaneous reduction to combined ventricular output (CVO) by ~50%. Since the lungs are still filled with fluid, PVR is high thus right ventricular output is still diverted away from the pulmonary circulation, through the DA. Right Panel: Removal of lung liquid and aeration of the lung results in a rapid fall in PVR and a subsequent increase in PBF, allowing 100% of right ventricular output to enter the lungs. This allows the pulmonary circulation to replace the placenta as the source of left ventricular output. There is also a reversal in pressure gradient and thus direction of blood flow across the ductus arteriosus (from left-to-right to right-to-left), allowing for up to 50% of left ventricular output to enter the pulmonary circulation, thus further stabilizing the upper body circulation.