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
viii
, A Physiologic Approach
to Neonatal Resuscitation
Stuart B. Hooper, Arjan B. te Pas and Roberts Ca/um T. Roberts
INTRODUCTION the physiologic changes that occur at birth and highlight
Neonatal resuscitation is commonly defined as the assistance approaches that may best assist different subgroups of infants
given to infants immediately after birth as they transition to as their physiology changes. Many well-informed, recent
newborn life. From a physiologic perspective, this transition publications have already detailed the currently recom-
involves some of the most complex and profound changes mended strategies for un_g_er aking neonatal resuscitation
that any human will likely encounter during their life. The from a practical Rerspective (Weiner et al, 2018). We intend
airways that are filled with liquid during fetal life must be to take a different approach and will focus on the physiology.
cleared to allow the entry of air and onset of pulmonary gas This is because currently recommended strategies for neona-
exchange, and major vascular shunts must close to separate tal resuscitation will likely change as our understanding of
the pulmonary and systemic circulations. It is truly an amaz- the pt.siology improves and better strategies for facilitating
ing feat of nature that the vast majority of infants transition the necess ry physiologic changes are identified. Indeed,
through these changes with such apparent ease. As a result, it much of, the evidence underpinning current neonatal resus-
is easy to underestimate both the magnitude of the physio- citati0n guidelines is regarded as weak and/or absent
logic changes and the complexity and difficulty of rendering SPerlman et al, 2015). The reasons for this are unclear, but it
assistance to infants struggling to adapt to life after birth. could be argued that a lack of scientific clarity regarding the
Very preterm infants commonly require assistance at birth physiology of transition is a major contributing factor.
because they are simply too immature to survive unassisted, Nevertheless, in the following discussion, it will become
but there is considerable debate about what assistance is evident that some of the emerging science is not consistent
required and how it should be provided. Nevertheless, a fun- with current recommendations. This should not be misinter-
damental tenet of neonatal resuscitation is to recognize that preted as a recommendation for changing practice, but as the
at birth, newborn infants, particularly ery Rreterm infants, first important step in designing studies that will provide the
are not "mini adults" but are essentially exteriorized fetuses required level of evidence needed to better guide practice.
with liquid-filled airways. As such, the type of assistance
given should be tailored to suit the infant's changing physiol-
ogy and its specific needs at any moment in time. For ESTABLISHING PULMONARY VENTILATION
instance, what is the logic of applying ventilation strategies
that facilitate pulmonary gas exchange when the gas exchange
CASE1
regions of the lung are liquid filled and so no pulmonary gas You are called to the delivery room to resuscitate a late pre-
exchange can occur? Although this is only a transient consid- term infant born at 34 weeks' gestation by repeat cesarean
eration for most infants, because the airways are rapidly section. The 1 min Apgar score is 2. You arrive at 90 sec of life.
cleared of liquid, it is a lingering consideration in very The infant is pale with a heart rate of 30 beats/min. The
preterm infants who have problems aerating their lungs infant is receiving nCPAP with 100% oxygen, but only gasp-
(te Pas et al, 2008). ing intermittently. The Sao 2 reading on the pulse oximeter is
A key component to a successful neonatal resuscitation is 65%. The anesthesiologist has just begun chest compressions.
understanding the physiologic changes that occur after birth
and having the capacity to monitor the infant as it progresses Exercise 1
through these changes so that the right assistance can be Question
provided at the right time. As such, rather than utilizing an What is the next most appropriate next step in this infant's
algorithm-based approach for describing currently recom- resuscitation, and what should have been done before you
mended strategies for neonatal resuscitation, we will discuss arrived?
1
, 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 BEFORE BIRTH expanding the chest wall and increasing interstitial tissue
pressures, essentially making the lung edematous.
AND DURING LABOR 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
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
viii
, A Physiologic Approach
to Neonatal Resuscitation
Stuart B. Hooper, Arjan B. te Pas and Roberts Ca/um T. Roberts
INTRODUCTION the physiologic changes that occur at birth and highlight
Neonatal resuscitation is commonly defined as the assistance approaches that may best assist different subgroups of infants
given to infants immediately after birth as they transition to as their physiology changes. Many well-informed, recent
newborn life. From a physiologic perspective, this transition publications have already detailed the currently recom-
involves some of the most complex and profound changes mended strategies for un_g_er aking neonatal resuscitation
that any human will likely encounter during their life. The from a practical Rerspective (Weiner et al, 2018). We intend
airways that are filled with liquid during fetal life must be to take a different approach and will focus on the physiology.
cleared to allow the entry of air and onset of pulmonary gas This is because currently recommended strategies for neona-
exchange, and major vascular shunts must close to separate tal resuscitation will likely change as our understanding of
the pulmonary and systemic circulations. It is truly an amaz- the pt.siology improves and better strategies for facilitating
ing feat of nature that the vast majority of infants transition the necess ry physiologic changes are identified. Indeed,
through these changes with such apparent ease. As a result, it much of, the evidence underpinning current neonatal resus-
is easy to underestimate both the magnitude of the physio- citati0n guidelines is regarded as weak and/or absent
logic changes and the complexity and difficulty of rendering SPerlman et al, 2015). The reasons for this are unclear, but it
assistance to infants struggling to adapt to life after birth. could be argued that a lack of scientific clarity regarding the
Very preterm infants commonly require assistance at birth physiology of transition is a major contributing factor.
because they are simply too immature to survive unassisted, Nevertheless, in the following discussion, it will become
but there is considerable debate about what assistance is evident that some of the emerging science is not consistent
required and how it should be provided. Nevertheless, a fun- with current recommendations. This should not be misinter-
damental tenet of neonatal resuscitation is to recognize that preted as a recommendation for changing practice, but as the
at birth, newborn infants, particularly ery Rreterm infants, first important step in designing studies that will provide the
are not "mini adults" but are essentially exteriorized fetuses required level of evidence needed to better guide practice.
with liquid-filled airways. As such, the type of assistance
given should be tailored to suit the infant's changing physiol-
ogy and its specific needs at any moment in time. For ESTABLISHING PULMONARY VENTILATION
instance, what is the logic of applying ventilation strategies
that facilitate pulmonary gas exchange when the gas exchange
CASE1
regions of the lung are liquid filled and so no pulmonary gas You are called to the delivery room to resuscitate a late pre-
exchange can occur? Although this is only a transient consid- term infant born at 34 weeks' gestation by repeat cesarean
eration for most infants, because the airways are rapidly section. The 1 min Apgar score is 2. You arrive at 90 sec of life.
cleared of liquid, it is a lingering consideration in very The infant is pale with a heart rate of 30 beats/min. The
preterm infants who have problems aerating their lungs infant is receiving nCPAP with 100% oxygen, but only gasp-
(te Pas et al, 2008). ing intermittently. The Sao 2 reading on the pulse oximeter is
A key component to a successful neonatal resuscitation is 65%. The anesthesiologist has just begun chest compressions.
understanding the physiologic changes that occur after birth
and having the capacity to monitor the infant as it progresses Exercise 1
through these changes so that the right assistance can be Question
provided at the right time. As such, rather than utilizing an What is the next most appropriate next step in this infant's
algorithm-based approach for describing currently recom- resuscitation, and what should have been done before you
mended strategies for neonatal resuscitation, we will discuss arrived?
1
, 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 BEFORE BIRTH expanding the chest wall and increasing interstitial tissue
pressures, essentially making the lung edematous.
AND DURING LABOR 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
