The fetal circulation

Abstract

The fetal circulation (Fig. 1) is markedly different from the adult circulation. In the fetus, gas exchange does not occur in the lungs but in the placenta. The placenta must therefore receive deoxygenated blood from the fetal systemic organs and return its oxygen rich venous drainage to the fetal systemic arterial circulation. 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. Thus, the fetal circulation can be defined as a 'shunt-dependent' circulation. © The Board of Management and Trustees of the British Journal of Anaesthesia [2005] All rights reserved.