Chapter 34: Pediatric Surgery
Which of the following statements regarding fetal physiology is correct?
(A) The circulatory pattern of the fetus is two ventricles working in series, rather than in parallel as in an adult.
(B) The right ventricle ejects highly oxygenated blood to the most metabolically active tissues.
(C) There are three components of venous return in the fetus: superior vena cava (SVC), inferior vena cava (IVC), and pulmonary veins.
(D) Renal blood flow is 3–5% of fetal cardiac output.
(E) Fetal water homeostasis relies primarily on fluid generated by the fetal lung.
(D) Neonatal and infant physiology is considerably different from an adult. The circulatory pattern of the fetus is unique in that the lungs are bypassed, and intracardiac/extracardiac shunts enable blood to be oxygenated (Fig. 34-19). Shunts (foramen ovale, ductus arteriosus, and ductus venosus) allow the fetus to receive blood from both ventricles, commonly referred to as parallel circulation. Adults experience a circulatory pattern in series that allows for an equal but separate output for each ventricle.
FIGURE 34-19. Fetal circulation AAo = Ascending aorta; CS = Crista dividens; DA = Ductus arteriosus; DAo = Descending aorta; DV = Ductus venosus; FO = Foramen ovale; IVC = Inferior vena cava; LA = Left atrium; LV = Left ventricle; MPA = Main pulmonary artery; PAs = Pulmonary arteries; RA = Right atrium; RV = Right ventricle; SVC = Superior vena cava; UA = Umbilical artery; UV = Umbilical vein; (from Rudolph CD, Rudolph AM, Lister GE, First LR, Gershon AA, eds. Rudolph’s Pediatrics. 22nd ed. New York, NY: McGraw-Hill; 2011: Fig. 483-3. Copyright © The McGraw-Hill Companies, Inc. All rights reserved).
The right ventricle receives relatively deoxygenated blood and ejects the majority of its output to the placenta. The left ventricle receives relatively highly oxygenated blood and ejects the majority of its output to the most metabolically active tissues. There are five components of venous return in the fetus: the upper body systemic venous return via the SVC; the lower body systemic venous return via the IVC; the placental return, also via the IVC; the coronary venous return, primarily via the coronary sinus (CS); and the pulmonary venous return via the pulmonary veins.
Renal blood flow is 3–5% of fetal cardiac output during the last trimester of gestation and increases to 12–16% during the first year of life. This is due to the relatively high vascular resistance of the fetal kidney, which decreases within the first 48 h after birth as a result of increase perfusion of the renal glomeruli. The decrease in vascular resistance is also responsible for ...