FETAL PHYSIOLOGY

QUESTION 1:
When assessing the fetus at birth:
A. 90% of all infants have 1-minute Apgar scores of 8 or more
B. the 5-minute Apgar score correlates well with acidosis and survival
C. it is abnormal for a neonate to have  cyanosed extremities beyond 60 seconds of age
D. the normal heart rate of a term neonate is between 100 and 120 beats per minute
E. the Apgar scoring system was devised by Dr. Virginia

QUESTION 2:
Concerning perinatal respiratory physiology, all of the following are true EXCEPT:
A. at term, the fetal lung contains about 30 ml/kg of an ultrafiltrate of plasma
B. the fetal lung does not usually contain amniotic fluid
C. approximately 2/3 of the lung fluid is expelled during the birth process
D. babies born by cesarean section have about the same amount of lung fluid as babies born vaginally
E. small preterm infants born vaginally frequently have excess lung water

QUESTION 3:
Concerning cardiovascular physiology after birth, all of the following are true EXCEPT:
A. the pulmonary vascular resistance decreases
B. pressures on the left side of the heart increases
C. completion of closure of the ductus arteriosus requires adequate arterial muscle tissue
D. mechanical closure of the ductus arteriosus occurs after 2 to 3 days
E. events during anesthesia may cause a return to fetal circulation

ANSWER 1
A. The 1-minute Apgar score correlates well with acidosis and survivial, and the 5-minute score may be predictive of neurologic outcome. Infants very frequently have a bluish tinge at the moment of birth, but at 60 seconds of age, most are entirely pink except for their hands and feet, which remain blue.  The normal heart rate of a term neonate is 120 to 160 beats per minute. Dr. Virginia Apgar first introduced her scoring system in 1953.

ANSWER 2
D. About 50 to 150 ml/kg/day of fluid is produced by a fetal lung at term (an ultrafiltrate plasma).  This fluid is expelled into the mouth where it is either swallowed or released into the amniotic fluid.  Normally the lung fluid contains no amniotic fluid, but if the depth of fetal breathing increases (such as during stress) some may be drawn in.  During the normal birth process the muscles of the vagina and pelvic floor squeeze the fetal chest and expel about 2/3 of the lung fluid.  the remainder being removed by capillaries, lymphatics, and breathing.  If this vaginal squeeze does not take place, infants may have excess lung water and respiratory difficulties.  This may occur after cesarean section (especially if there has been no previous labor) and in small preterm infants.

ANSWER 3:
D. At birth, the pulmonary vascular resistance decreases dramatically in response to lung expansion, increased pH, and a rise in alveolar oxygen tension.  This reduces the pulmonary artery pressure and increases pulmonary blood flow.  The increased amount of blood returning to the left atrium raises the pressures in the left atrium closing the foramen ovale.  The ductus arteriosus closes primarily in response to increased oxygen tension.  This is functional closure, but complete mechanical closure requires adequate arterial muscle and occurs after 10 days or more.


Questions from McGraw-Hill Specialty Board Review (6th ed.)