Workbook in Practical Neonatology 6th Edition by Richard Polin

ANSWER KEYS INCLUDED




WORKBOOK

,V I D E O TA B L E O F C O N T E N T S

Video 16-1: Echocardiogram—Relationship of Ventricles and Great Vessels
Video 16-2: Fluoroscopic Image of Balloon Atraial Septostomy
Video 16-3: Echocardiogram—Ebstein’s Anomaly
Video 16-4: Echocardiogram—Stenotic Pulmonary Valve
Video 16-5: Fluoroscopic Image of Pulmonary Balloon Valvoplasty
Video 19-1: Benign Neonatal Seizure




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, 2 CHAPTER 1 A Physiologic Approach to Neonatal Resuscitation

Answer into lung tissue (Olver et al, 1986). This reverses the osmotic
Positive pressure ventilation should have been started gradient for liquid movement across the airway epithelium,
immediately. leading to liquid reabsorption, rather than secretion as occurs
From a teleologic perspective, it is logical that the physio- in utero. However, Na1 reabsorption requires high levels of
logic changes required for survival after birth are triggered by adrenaline, is relatively slow, only arises late in gestation, and
the one event that cannot occur in utero, lung aeration. so is not active in very preterm infants (Hooper et al, 2016).
Aerating the lung and establishing pulmonary ventilation Similarly, as cesarean section delivery in the absence of labor
triggers the physiologic changes that underpin the transition avoids the stress of labor, this mechanism is unlikely to be
to newborn life (Hooper et al, 2015a). However, it is far too activated in infants delivered by cesarean section without
simplistic to assume that the primary benefit of “establishing labor (Jain and Eaton, 2006).
pulmonary ventilation” is reestablishing oxygen and carbon Partial airway liquid clearance can also occur during labor
dioxide exchange lost following umbilical cord clamping. as a result of induced postural changes before and during
Lung aeration not only triggers the switch to pulmonary delivery of the head (te Pas et al, 2008). The fetus is forced
gas exchange but also triggers a very large reduction in pul- into an exaggerated “fetal position” with the enhanced dorso–
monary vascular resistance (PVR), which initiates a series ventral flexion causing an increase in abdominal pressure and
of cardiovascular changes that are also essential for survival rostral displacement of the diaphragm (Harding et al, 1990).
after birth (see later). Positive pressure ventilation also This increases intrathoracic pressures and forces liquid to
enhances reabsorption of lung fluid. leave the lungs via the trachea (Hooper and Harding, 1995;
Harding and Hooper, 1996). As the fetal respiratory system is
highly compliant, only small increases in intrathoracic pres-
CASE 1 CONTINUED sure are needed for large reductions in airway liquid volumes
With initiation of positive pressure ventilation, the heart rate (Hooper and Harding, 1995; Harding and Hooper, 1996).
increases to 120/min and the saturation increases to 85% by Although this mechanism is applicable to infants born
7 min of life. The infant is breathing regularly at 120 breaths/ vaginally, as per Na1 reabsorption, it is not readily applicable
min. Auscultation reveals fine rales and wet sounding rhon- to infants born by cesarean section, particularly in the
chi. You suspect the infant has a “wet lung syndrome.” absence of labor.
Exercise 2 Airway Liquid Clearance After Birth
Question Lung aeration has significant implications for respiratory
When is lung liquid reabsorbed? How did the mode of deliv- function in the newborn period, and to better understand
ery influence the resorption of lung liquid? these consequences, the process of lung aeration can be
divided into a series of phases that give rise to separate
Answer challenges (Hooper et al, 2016).
Resorption of lung liquid begins antenatally and continues 1. The first phase commences at birth with liquid-filled air-
during labor and delivery. However, most lung liquid is reab- ways, and so the primary challenge is to clear the airways
sorbed postnatally when spontaneous or assisted ventilations of liquid, which occurs across the distal airway wall.
begin. Infants delivered by cesarean section do not undergo 2. Airway liquid is cleared from the airways into the sur-
the postural changes of vaginally delivered infants; those rounding lung tissue at a much greater rate (over minutes)
changes help to expel liquid from the lungs. than it is cleared from the tissue (over hours). As such,
airway liquid accumulates within lung tissue for the first
few hours after birth, forming “perivascular fluid cuffs,”
AIRWAY LIQUID CLEARANCE expanding the chest wall and increasing interstitial tissue
BEFORE BIRTH AND DURING LABOR pressures, essentially making the lung edematous.
3. Airway liquid is gradually cleared from lung tissue via the
Although there is some evidence to suggest that airway liquid circulation and lymphatics, after which lung function and
clearance begins late in gestation before labor onset (Jain and mechanics stabilize.
Eaton, 2006), this is not a consistent finding, and the role of
experimental artefacts is unclear with regard to the original Exercise 3
observations (Harding and Hooper, 1996). Nevertheless, con- Question
sidering the capacity of the lung to clear airway liquid during What is the importance of spontaneous breathing (or posi-
labor and after birth (see later), whether small amounts of tive pressure ventilation) on promoting the clearance of lung
liquid are cleared before labor appear inconsequential. How- water?
ever, it is clear that airway liquid clearance can begin during
labor and vaginal delivery (Olver et al, 2004). The release of Answer
adrenaline in response to the stress of labor activates Na1 To clear lung liquid from the airways and alveoli, positive
channels located on the luminal surface of airway epithelial pressure ventilation (either spontaneous or assisted) must
cells, which promotes Na1 reabsorption from the airways begin. Ventilation moves the liquid through the airways to