The fluid shift from the vascular compartment immediately after birth

Abstract

Immediately after birth there is a rise in concentration of Hb and in PCV in the majority of infants. The rise may be discernible within a few minutes of birth and is probably completed within an hour or two. It occurs in the absence of any transfer of placental blood. The possible causes are considered in detail and it is concluded that the effect is brought about by a shift of fluid from the vascular compartment. This fluid is mainly whole plasma, and its volume may amount to a large fraction of the circulating plasma at birth, a quarter or more. In addition, there is a shift of fluid from the red cells, the volume of red cells contracting after birth by an average of 3%. The cause of these fluid shifts is discussed and it is suggested that the plasma loss may be a consequence of the re-routing of the circulation after birth. These results imply that the foetus in utero is hydraemic, i.e. has a large plasma volume. Haemodilution is thus in part responsible for the wide range of the normal cord Hb level. Possible clinical implications are mentioned, particularly in relation to the pulmonary failure of the premature infant.