RT Journal Article
SR Electronic
T1 A physiological approach to the timing of umbilical cord clamping at birth
JF Archives of Disease in Childhood - Fetal and Neonatal Edition
JO Arch Dis Child Fetal Neonatal Ed
FD BMJ Publishing Group Ltd and Royal College of Paediatrics and Child Health
SP F355
OP F360
DO 10.1136/archdischild-2013-305703
VO 100
IS 4
A1 Stuart B Hooper
A1 Graeme R Polglase
A1 Arjan B te Pas
YR 2015
UL http://fn.bmj.com/content/100/4/F355.abstract
AB Umbilical cord clamping at birth has a major impact on an infant's cardiovascular system that varies in significance depending upon whether the infant has commenced breathing. As umbilical venous return is a major source of preload for the left ventricle during fetal life, recent experimental evidence has shown that clamping the umbilical cord severely limits cardiac venous return in the absence of pulmonary ventilation. As a result, cardiac output greatly reduces and remains low until breathing commences. Once the infant begins breathing, aeration of the lung triggers a large increase in pulmonary blood flow, which replaces umbilical venous return as the source of preload for the left ventricle. As a result, cardiac output markedly increases, as indicated by an increase in heart rate immediately after birth. Thus, infants born apnoeic and hypoxic and have their cords immediately clamped, are likely to have a restricted cardiac output combined with hypoxia. As increased cardiac output is a major physiological defence mechanism that counteracts the effects of hypoxaemia, limiting the increase in cardiac output exposes the infant to ischaemia along with hypoxia. However, if the infant commences breathing, aerates its lungs and increases pulmonary blood flow before the umbilical cord is clamped, then pulmonary venous return can immediately take over the supply of left ventricular preload upon cord clamping. As a result, there is no intervening period of reduced preload and cardiac output and the large swings in arterial pressures and flows are reduced leading to a more stable circulatory transition.