P2.ii · Foetal Circulation

This Viva will explore your understanding of the physiology of transition at birth. What is the normal haemoglobin saturation of a newborn breathing air? Subsequent questions explored knowledge of foetal haemoglobin oxygen dissociation curve, foetal/newborn circulation, changes at birth, normal values of newborn vital signs such as respiratory rate, heart rate, blood pressure, oxygen saturation.

This Viva relates to the respiratory changes of pregnancy at term, hypoxaemia and the foetal circulation. Q 1. Describe the respiratory changes in pregnancy at term. Subsequent questions sought a description of ABG at term pregnancy, physiological mechanism to explain an increased A-a gradient, causes of a low PaO2 in a patient with a normal A-a gradient, the response of hypoxemia to supplemental O2 when the A – a gradient is normal and when abnormal, and a description of the foetal circulation and the changes that occur at birth.

Candidates were expected to identify the major features on a diagram of the foetal circulation. Additional questions concerned the changes to this that occur with birth (Syllabus section P and O1), the haemoglobin oxygen dissociation curve (B1 h), the factors that impact on this and the significance of these changes. Syllabus : P, O1, B1h