Anaesthesia | Obstetrics | The Fetal Circulation

The Fetal Circulation
Session Overview
Description
This session describes circulation and oxygen delivery in the fetus with particular reference to control of the fetal circulation and the transition to the neonatal circulation at birth.

Learning Objectives
By the end of this session you will be able to:

• Describe the fetal circulation
• List the major factors influencing the fetal circulation and the circulatory changes at birth
• Describe the process of gas transfer across the placenta and oxygen delivery to the fetus
• List the major factors influencing drug transfer across the placenta

Fetal circulation is markedly different from adult circulation.

In the fetus, gas exchage does not occur in the lungs but in the placenta. The placenta receives deoxygenated blood from the umbilical arteries and returns oxygenated blood to the fetus via the umbilical vein (Fig 1).

In addition, the fetal cardiovascular system is designed in such a way that the most highly oxygenated blood is delivered to the myocardium and brain.

These circulatory adaptations are achieved in the fetus by both the preferential streaming of oxygenated blood and the presence of intracardiac and extracardiac shunts. Therefore, the fetal circulation can be defined as a 'shunt-dependent' circulation.

It is important for anyone involved in obstetric and paediatric anaesthesia to understand the distinction between fetal and neonate circulation.