This chapter is relevant to Section G1(v) of the 2017 CICM Primary Syllabus, which asks the exam candidate to "describe the circulatory and respiratory changes that occur at birth". This has never been the subject of any First part questions, but appears extensively in the old pre-2007 Fellowship papers (Question 10 from the second paper of 2007, Question 11 from the first paper of 2005, Question 6 from the first paper of 2001). "The transfer from the fetal to the neonatal state is complex", says the college model answer helpfully, though it is not clear how making this statement in one's written answer would have contributed to one's marks. Fortunately, the circulatory events at birth can be summarised by saying that the normal extrauterine pattern of circulation results in the pressure-driven closure of the foramen ovale and ductus arteriosum.
In brief summary:
At birth,
- Lungs are aerated with the first breaths (which purges liquid and creates and FRC) and with crying (which maintains the FRC)
- This decreased pulmonary vascular resistance
- At the same time, systemic vascular resistance is increased by clamping the umbilical cord
- Right ventricular output is thereby channeled into the pulmonary circulation instead of the systemic
- Increased pulmonary blood flow and increased systemic vascular resistance results in increased left atrial pressure, reversing the flow across the foramen ovale (which therefore closes immediately)
- Increased aortic pressure reverses flow across the ductus arteriosus, which closes over around 24 hours (at least functionally - anatomic closure takes several days)
- Closure of these structures leads to the separation of the pulmonary and systemic circulations, which concludes the transition to the adult pattern of circulation.
Causes of a persistent foetal circulation:
- Low lung volume states (e.g. hyaline membrane disease and perinatal asphyxia)
- Pulmonary hypoplasia (e.g. diaphragmatic hernia and Potter’s syndrome)
- Meconium aspiration
- Chronic placental insufficiency
- Sepsis
- Hyperviscosity syndrome
- Perinatal hypoxia, hypothermia and acidosis from any cause
- Pulmonary thromboemobolism
Causes of reversion to foetal circulation:
- Medical or surgical (eg. infusion of prostaglandin E2 to maintain an open ductus arteriosus in cases of duct-dependent congential heart disease, eg. transposition of the great arteries)
- Hypoxia, hypothermia and acidosis from any cause - occurring in the critical period before permanent closure of the ductus arteriosus and foramen ovale
Probably the single best resource for this is Chris Nickson's entry in LITFL, which is exactly all you need to know and nothing more. Oh's Manual dedicates haf a page to the topic, at the beginning of Shelley D. Riphagen's chapter (Ch.103, p. 1071: "The Critically Ill Child"). A short but highly examinable list of reasons for postnatal reversion to foetal circulation is also available there, and is reproduced below with little modification. If for whatever reason your situation calls for a more detailed knowledge of the topic, there is an excellent article by van Vonderen et al (2014) which explores not only the physiological changes at birth but the methods we have used to investigate them, and the historical changes in this branch of human biology. Wherever no other specific reference is mentioned, this article was the main source for the content offered here.
These diagrams are from van Vonderen et al (2014):
In textual long form, which defeats the point of point form:
An excellent resource for this is D'cunha et al (2001). In short, a persistently foetal pattern of circulation is mainly caused by anything which keeps pulmonary vascular resistance high. That could be a whole host of causes. The linked article organises them into acute or chronic:
Chronically increased PVR in a structurally normal heart
Acutely increased PVR due to physiological pulmonary vasoconstriction
Causes of perinatal hypoxia, acidosis and hypothermia
Murphy, Peter John. "The fetal circulation." Continuing Education in Anaesthesia, Critical Care & Pain 5.4 (2005): 107-112.
Kiserud, Torvid. "Physiology of the fetal circulation." Seminars in Fetal and Neonatal Medicine. Vol. 10. No. 6. WB Saunders, 2005.
Kiserud, Torvid, and Ganesh Acharya. "The fetal circulation." Prenatal Diagnosis: Published in Affiliation With the International Society for Prenatal Diagnosis 24.13 (2004): 1049-1059.
Fishman, Alfred P., and Dickinson W. Richards. "Physiological changes in the circulation after birth." Circulation of the Blood. Springer New York, 1982. 743-816.
van Vonderen, Jeroen J., et al. "Measuring physiological changes during the transition to life after birth." Neonatology 105.3 (2014): 230-242.
Koos, Brian J., and Arezoo Rajaee. "Fetal breathing movements and changes at birth." Advances in Fetal and Neonatal Physiology. Springer New York, 2014. 89-101.
Hooper, Stuart B., et al. "Cardiovascular transition at birth: a physiological sequence." Pediatric research (2015).
D’cunha, Chrysal, and Koravangattu Sankaran. "Persistent fetal circulation." Paediatrics & child health 6.10 (2001): 744.