“Cyanotic Congenital Cardiac Defects: Diagnosis & Therapy” by Tom Kulik, MD, for OPENPediatrics

August 31, 2019 0 By Bertrand Dibbert


Cyanotic Congenital Cardiac Defects: Diagnosis
and Therapy, by Doctor Tom Kulik. I’m doctor Tom Kulik. I’m a pediatric cardiologist
and cardiac intensivist at the Children’s Hospital, Boston. This lecture will be the
second part of two lectures in regards to the diagnosis and management of the infant
with cyanosis. Introduction. To briefly preview the lecture, we will first
review the physiology of cyanosis that was covered in the first of these two lectures.
We will discuss general diagnostic considerations. We will briefly go over some of the most important
types of cyanotic heart disease, especially the types that are present in the neonate.
And we will discuss ICU based therapy. And by that we’re not going to talk about surgical
palliation, or surgical correction of these lesions, but rather focus on the sort of things
that the neonatologist and intensivist will be involved with in their unit– stabilizing
and preparing the baby for more definitive treatment. Physiology. Let’s briefly talk about the physiology
of cyanosis caused by congenital heart defects and review material that we had previously
discussed. There are basically four types of physiological reasons why babies are cyanotic.
They can have right to left intraventricular shunt, as illustrated here by a baby with
Tetralogy of Fallot. In this case, there was a ventricular septal defect and outflow obstruction
between the right ventricle and pulmonary artery. Hence, blood tends to go right to
left across the VSD into the aorta. Right to left, interatrial shunting. In this
case, it’s a baby that has severe pulmonary stenosis. The obstruction to blood flow from
the right ventricle to the pulmonary artery is so severe that an entire cardiac output
cannot be injected into the lungs, and hence, there’s a considerable amount of right to
left shunting at the atrial level, not ventricular level. Let’s talk about what I might term
simple, or perhaps more commonly termed, complete mixing. And what you see here is an example
of a baby that has a particular type of single ventricle lesion called tricuspid atresia.
In this case, there is what I might term simple or complete mixing of blue system venous blood
with red pulmonary venous blood. And as a result, there is a cyanosis. And finally, transposition physiology is the
physiology that occurs in babies that have a D-transposition of the great vessels. That
is to say the aorta is attached to the right ventricle and the pulmonary artery to the
left ventricle. In which case, there tend to be two separate circuits whereby the blue
blood coming back from the body to the heart is ejected right back out to the body again,
and red blood from the lungs is re-ejected to the lungs. These patients can only survive
ex-utero by virtue of some degree of mixing of the red and blue streams. And we will discuss
this a little bit more in just a few minutes. There are multiple determinants of arterial
oxygen saturation in congenital heart disease. They can pretty much be boiled down to these
five factors. The first is pulmonary venous oxygen saturation. Obviously, a baby with
congenital heart lesion will be bluer than he or she would otherwise be if there is lung
disease, and hence, the pulmonary venous blood is not fully saturated. The ratio of pulmonary
to systemic blood flow, also known as Qp:Qs, is very important in babies with either complete
mixing lesions, or even a simple right to left shunting. The amount of systemic blood
flow, the hemoglobin content of the blood, and the total body O2 consumption are also
important in determining arterial oxygen saturation. And the reason for this is that whenever there
is right to left shunting, the blue blood returning from the body tends to, essentially,
dilute out the oxygen level of the red blood returning from the lungs. The bluer the blue
blood is, the less red the arterial blood will be as it’s ejected from the heart. So
as systemic blood flow falls, mixed venous oxygen saturations also tend to fall. With
less O2 delivery to the body because of lower hemoglobin, the mixed venous O2 saturation
tends to fall. And as more oxygen is extracted because of high oxygen consumption, that also
tends to negatively impact the oxygen saturation of the venous blood. So these are the key determinants of arterial
O2 saturation in just about any congenital heart lesion. Perhaps the only exception to
that is D-transposition of the great arteries. And there, the key issue is how much mixing
of the red blood and the blue blood streams occurs. And again, we’ll talk about this a
bit more in a few minutes. Diagnostic Considerations. Let’s move on to general diagnostic considerations.
We’re going to focus primarily on the clinical characteristics which help discriminate congenital
heart disease from lung disease and persistent pulmonary hypertension of the newborn. We’re
not going to try to provide enough information to allow one to make a specific diagnosis
of a heart defect without performing an echocardiogram, because echo is really the definitive way
we make these diagnoses in the vast majority of cases. So I’m going to emphasize for the
next few minutes the things that one can observe in a baby in terms of physical signs and symptoms
that make one most concerned about the possibility of a congenital defect, and hence initiating
prompt detailed evaluation of such. So let’s talk about these red flags for congenital
heart disease. The first is babies that are cyanosis with what one of the kind of founding
fathers of pediatric cardiology, Alex Nadas, termed “happy tachypnea.” Happy tachypnea
is tachypnea without dyspnea, or a baby who’s breathing fast but very easily. Babies with
lung disease of course tend to have dyspnea because their lungs are relatively non-compliant.
On the other hand, babies with congenital heart disease tend to have very compliant
lungs, and hence, although they will be tachypnic because of a hypoxic respiratory drive, they
don’t tend to breathe particularly hard. And so happy tachypnea tends to make one think
more of heart disease and less of lung disease. Now, one has to be careful though. There is
a particular type of heart lesion, total anomalous pulmonary venous connection, that is to say,
when all the pulmonary veins returning from the lungs have obstruction somewhere between
their origin and the heart, these babies can develop very severe pulmonary edema as is
illustrated on this chest x-ray of a young patient with total obstructed veins. And these
babies will have a considerable amount of dyspnea. So one always has to keep obstructive
total veins in mind when presented with the cyanotic baby that has a lung finding suggestive
of pulmonary edema. The second red flag for congenital heart disease
is differential cyanosis. Differential cyanosis is when the oxygen saturations are different
in the right arm versus the lower body. And there are basically two types of differential
cyanosis. The first is differential cyanosis due to right to left shunting of systemic
venous blood into the descending aorta. This can occur under two circumstances. One is persistent pulmonary hypertension of
the newborn. Babies that have this particular disease have very high pulmonary resistance.
And if they have an open ductus, especially a large open ductus, they may actually shunt
blood from the pulmonary artery into the descending aorta, such that their oxygen saturations
in their right arm will be considerably higher than in their legs. Not all babies with PPHN
have differential cyanosis, but certainly many of them do. Those same findings however, can occur in
babies with congenital heart lesions. For example, I’ve shown a baby with interruption
of the aortic arch. In this particular set of circumstances, all of the profusion to
the lower body is via the right ventricle across the ductus And so these kids will tend
to have substantially lower oxygen saturation in the lower extremities than in the right
arm. So differential cyanosis, while it can occur without a congenital heart lesion, specifically
with PPHN, can also occur with certain forms of heart disease. The second flavor, if you will, of differential
cyanosis is reverse differential cyanosis. And with reverse differential cyanosis, the
oxygen saturations are actually higher in the lower body than in the right arm. And
where this is occasionally seen, and I think pretty much the only time it’s occasionally
seen, is in babies with d-transposition of the great vessels or a very similar anatomic
lesion. In this case, if there is very high resistance
to blood flow in the lungs, and there’s a patent ductus arteriosis, when the left ventricle
ejects blood into the pulmonary artery, a certain fraction of it will tend to go across
the ductus into the descending aorta. Since this is red pulmonary venous blood, these
patients will actually tend to have higher oxygen saturation in the legs than in the
right arm. This can occur either because, as I just mentioned, high pulmonary vascular
resistance, or sometimes coarctation of the aorta in a d-transposition, where there is
narrowing of the isthmus of the aorta, the segment between the left subclavian artery
and the ductus. And that can also give reverse differential cyanosis. So the finding of reverse
differential cyanosis is very highly suggestive of congenital heart disease. Murmurs can constitute a third red flag for
congenital heart disease. As I think most folks know, very soft murmurs are very common
in babies, and grade one to two over six murmurs do not necessarily connote congenital heart
disease. On the other hand, murmurs of grade three intensity or louder are quite unusual
in otherwise normal babies, and certainly raise a red flag in a baby who has lower than
normal arterial oxygen saturations. Continuous murmurs in the back are also very uncommon
in otherwise normal newborns and make one think of a lesion like Tetrology of Fallot
with pulmonary atresia. And there is one murmur in particular, that
is to say, the to and fro, not so much continuous, but to and fro murmur at the left upper sternal
border, which is almost pathogenomic of babies that have absent pulmonary valve syndrome,
also known as Tetrology of Fallot absent pulmonary valve. There are very few other situations
in which a typical to and fro murmur like this is heard. So murmurs can sometimes put
one on the alert for congenital heart lesion. Point number four refers to the so-called
hyperoxia test, that is to say if one gives a baby with lung disease a very high inspired
oxygen, generally the PO2 will go up substantially or the O2 sat goes up substantially by virtue
of the fact that most babies that are cyanotic by virtue of lung disease have VQ mismatch
as a primary cause for this. And this is quite responsive to oxygen. One can read various
cut-off levels for arterial PO2 in response to 100% oxygen as discriminating between congenital
heart disease and lung lesions. I’ve used PO2 of 200, because it’s certainly possible
for babies with cyanotic mixing lesions to have PO2s of greater than 150 on 100% oxygen.
But to be quite honest this test doesn’t have a clear cut cut off. Babies with very severe lung disease may not
increase their arterial PO2s that much on 100% oxygen. On the other hand, babies with
certain forms of heart disease, for example, total anomolous pulmonary venous connection
below the diaphragm will occasionally have streaming pulmonary venous blood in such a
way that the arterial PO2 can actually be greater than 200 in the upper body. And so,
it’s very hard to give a discrete reliable cut off for the hyperoxia test. I think it
would be safe to say that any PO2s less than 200 or even somewhat greater than that, would
make one have to consider the possibility of congenital heart defects. And in fact, probably a more sophisticated
way to think about this, although a non-quantitative way, is to consider that whenever the arterial
PO2 is out of proportion to the chest x-ray, one is concerned about congenital heart defects,
in particular relatively low PO2s, despite a normal chest x-ray. Again, one has to be
cautious. Babies with obstructed total anomalous pulmonary venous connection can have very
wet appearing chest x-ray, which might imply pneumonia, but in fact, is pulmonary edema
due to their congenital heart lesion. Electrocardiogram is generally normal in most
babies with cyanotic heart disease, and isn’t terribly useful in most cases. Therefore,
although the presence of left axis deviation, that is to say, QRS axis of less than a zero
does run along with certain forms of heart disease, cyanotic heart disease especially.
Tricuspid atresia certainly raises a red flag in the circumstances in which left axis deviation
occurs. Finally the chest x-ray can be helpful. Certainly
dextrocardia doesn’t prove the presence of congenital heart disease although it makes
quite likely. Midline stomach bubble, as one sees with hetrotaxy syndromes also markedly
increases the likelihood of congenital heart disease. Right aortic arch can be a finding
in a normal person, but it also suggests the possibility of Tetralogy of Fallot, truncus
arteriosus or transposition views to pulmonary stenosis. And a classic finding with babies
that have Tetralogy of Fallot or Tetrolagy of Fallot with pulmonary atresia is the upturned
cardiac apex combined with the flat pulmonary arterial segment on the chest x-ray and right
aortic arch as we see in this film of a baby with Tetralogy of Fallot in pulmonary atresia. Types of Cyanotic Congenital Heart Disease. So having discussed the sorts of physical
findings that make one concerned about heart disease, let’s talk about the specific types
of cyanotic heart disease that occur most often in babies with this lesion. We’re not
going to go over detailed descriptions, but I hope to provide enough information that
you’ll have a general idea of what you will be dealing with about 99% of the time when
dealing with cyanotic infants. And I’d like to break these lesions down into
what you might call a ductus-centric classification. That is to say, categorize the babies, the
patients, in this way– those that have severe obstruction to pulmonary blood flow and, therefore,
will require an open ductus and, therefore, Prostaglandin E1 for palliation. Number two,
babies that have little or no obstruction to pulmonary blood flow, in which case PGE-1
may not be either required or even helpful. The third type of classification are babies
with d-transposition of the great vessels. Those babies may benefit from an open ductus,
but not always. And finally, babies with a total anomalous pulmonary venous connection
with obstruction. In those cases, babies neither benefit from– in fact, they actually have
a deleterious effect from Prostaglandin E1. So let’s start with the first classification,
babies with severe obstruction to pulmonary blood flow, in which case Prostaglandin E1
is required therapy. The first would be babies with critical pulmonary stenosis or pulmonary
atresia. As I mentioned earlier in this lecture, babies with this particular lesion have such
a high degree of outflow obstruction between the right ventricle and the pulmonary artery,
that a full cardiac output cannot be ejected across this narrow pulmonary valve into the
lungs. And hence, there is a very large amount of right-left shunting at atrial level. There’s
a diagram of that on the left. On the right is a lateral view of an angiogram,
which is an injection into the right ventricle. And what you see here is a good-sized right
ventricle, but with relatively heavy trabeculations due to hypertrophy that’s occurred in utero
because of the very high right ventricular pressure. And you see a very thickened pulmonary
valve. Ordinarily, you can’t really see the pulmonary
valve very well on angiography and with a relatively small jet of contrast that goes
across it. This is kind of a typical angio of a baby with critical valvar pulmonary stenosis.
Because of the marked limitation of pulmonary blood flow in critical PS, patency of the
ductus is critical. Tetralogy of Fallot, if severe enough, can
present with life-threatening hypoxemia in a neonate because of a marked reduction in
pulmonary flow. I want to make the strong point, however, that most babies with Tetralogy
after they’re born, do not have severe obstruction to right ventricular outflow. Most neonatal
Tretralogies have quite adequate oxygen saturations without an open ductus, and really require
very little in the way of therapy. But in the case of a baby with severe obstruction,
Prostaglandin E1 may be required. There other lesions that are similar to Tetralogy of Fallot.
For example, double outlet right ventricle with pulmonary stenosis, that have much the
same physiology. Babies with single ventricle lesions that
have a high degree of obstruction to pulmonary blood flow also require Prostaglandin E1.
This is a diagram of a patient with tricuspid atresia. In the case of tri-atresia there
is basically no right ventricle, no tricuspid valve. And so systemic used blood goes from
the 2 cava into the right atrium, crosses the atrial septum into the left atrium and
mixes with pulmonary venous blood there, enters the left ventricle, some is ejected into the
aorta. And then some finds its way into the lungs, presuming there is an open VSD in a
sub-pulmonary chamber. If the VSD is quite restrictive, or the area
underneath the pulmonary artery is quite narrow, there may be a critical reduction in pulmonary
blood flow. In which case, Prostaglandin E1 won’t be required. Now, not all tricuspid
atresia babies have this critical reduction. Some do not require prostaglandins. But some
do. And this is true for other single ventricle defects that have restricted pulmonary blood
flow. Finally, this is a rare lesion. Even large
centers will see this only a very few times of the year. But it’s worth mentioning. Ebstein’s Malformation basically is when the
tricuspid valve is displaced into the right ventricle such the right ventricular mass
is reduced in functional volume. And the valve itself is very nonfunctional. So it tends
to have marked regurgitation. There’s a whole spectrum of Ebstein’s. Very
mild Ebstein’s is consistent with an asymptomatic long life. Very severe Ebstein’s shows up
in the way I’ve illustrated on this screen, with a baby that has a massively dilated heart
in utero and immediately ex-utero and a right ventricle that by virtue of the tricuspid
regurgitation, is basically insufficient to eject blood out the pulmonary artery and into
the lungs. These babies require an open ductus in order to provide adequate pulmonary blood
flow. The second general category of patients with
cyanotic heart disease are those that have little or no obstruction to pulmonary blood
flow and, therefore, do not require Prostaglandin E1 for palliation. As I mentioned before,
babies with Tetralogy of Fallot rarely need a ductus. Most do not have severe right ventricular
outflow obstruction. And so this would generally be the case for most babies with Tetralogy. Babies with Tetralogy of Fallot and so-called
MAPCAs, or Multiple Aortopulmonary Arteries, are patients that also oftentimes do not require
prostaglandin for palliation. Babies with this particular lesion are like Tetralogy
in the sense that there are two normal-sized ventricles and a ventricular septum defect.
The aorta generally comes off mostly the left ventricle. But instead of having some connection
between right ventricle and the pulmonary arteries, there is no connection. And blood
finds its way into the lungs either as through the so-called aortopulmonary collateral vessels
or, in some cases, through an ductus arteriosus. Babies that do not have a ductus arteriosus
and has supply through the aortopulmonary collateral vessels, of course, are not ductile
dependent. I’ve illustrated the angiogram on the right side of the slide as arrows pointing
to these collaterals that come directly of the aorta. These babies are not prostaglandin
dependent. Do hasten, however, to make note of the fact that some subset of babies with
Tetralogy of Fallot and pulmonary atresia will basically have their entire pulmonary
blood flow supplied via a ductus. And babies with that lesion do require an open ductus,
and hence, generally Prostaglandin E1 palliation. Babies with truncus arteriosus do not require
Prostaglandin E1 unless there is some additional lesion such as interruption of the aortic
arch. Babies with truncus basically have two normal-sized ventricles and a VSD. And then
there’s a single large vessel that arises from these two ventricles this gives rise
to both the aorta and pulmonary arteries. And this is not a ductile-dependent form of
cyanotic heart disease. Babies with single ventricle lesions that have no obstruction
to pulmonary blood flow do not require Prostaglandin E1 in order to maintain adequate pulmonary
blood flow. Now I hasten to make note of the fact that
some of these babies can have obstruction to their aorta, either flow from the ventricle
into the aorta or coarctation or other narrowing of the aorta. In that case, Prostaglandin
E1 may be required. But simply talking about babies with cyanotic defects, if there is
no obstruction to pulmonary blood flow in a single ventricle patient, there is no need
for a Prostaglandin E1 in order to maintain adequate pulmonary blood flow. In the case of babies with transposition of
the great arteries, Prostaglandin E1 may be helpful. As you recall, these babies require
mixing of the red and blue blood streams in order to provide adequate 02 delivery to the
body. This generally has to, at least in part, occur at the level of the atrial septum. Mixing
at the level of the ductus as a sole level of mixing is not adequate. But the presence of an open ductus can increase
pulmonary blood flow and augment mixing of the atrial level. And so for that, using Prostaglandin
E1 may be helpful in babies with transposition. Not all babies will adequately respond to
this, however. There is an occasional baby with d-Transposition
that actually becomes acutely ill after introduction of this medication for whatever reason. So
one has to keep this in mind. But by and large, maintaining ductile patency is helpful in
these patients with transposition. Babies with total anomalous pulmonary venous
connection, on the other hand, may actually be harmed by Prostaglandin E1. If these babies
have obstruction to pulmonary venous return to the heart, the resistance to blood flow
through the lungs is very high. In which case, if the ductus arteriosus is open, blood that’s
ejected from the right ventricle tends to go across the ductus into the descending aorta.
And hence, total pulmonary blood flow is reduced. So with total anomalous pulmonary venous connection,
one generally avoids the use of Prostaglandin E1. ICU Therapy. So finally, what is this ICU based therapy
that’s available for patients that are hypoxemic? Well, basically there are three things that
one needs to do in order to effectively apply this therapy. The first thing is to assess
and secure adequate O2 delivery for the patient. Even before one has a definitive diagnosis,
it’s necessary to attend to this. It’s important when assessing the baby from life-threatening
hypoxemia. And by the way to measure arterial oxygen saturations or PO2s. Transcutanious
oximeters are really not very accurate when the oxygen saturation is low and really aren’t
acceptable in many cases for determining whether a baby is seriously hypoxemic or merely has
a lower than normal oxygen level. It’s necessary to make ultimately an accurate
diagnosis and then eventually definitive therapy is applied, which is oftentimes surgical.
But there is a considerable amount of opportunity to make these patients better, even without
surgery. So what is life-threatening hypoxemia? At
least as far as I’m aware, there is no absolute arterial PO2 that qualifies for this. And so it’s very important to think not only
in terms of arterial saturation, but O2 delivery to the tissues. O2 delivery– the equation describes oxygen
delivery to the tissues– is very simple. It’s basically delivery equals content of
arterial content of oxygen, which is related to both the pulmonary venous, oxygen saturation,
as well as hemoglobin, and the systemic blood flow which is in a normal person– in a normal
heart– a cardiac output. One uses serum lactate since, to some extent,
serum bicarb levels are indicators of tissue dysoxia. I don’t think we know for sure that
a non-elevated lactate level necessarily implies that all organs, especially the brain, have
adequate O2 delivery. But as a general index of total O2 delivery sufficiency, a lack of
high lactates tends to be a somewhat reassuring. In general, I think one could say that with
acceptable hemoglobin and cardiac output, at least in newborn babies, arterial PO2s
in the low 20 range are tolerated at least for some period of time. And certainly, arterial
PO2s of greater than 25 seem to be well tolerated for at least some period of hours or perhaps
even longer. But again, I emphasize that it’s critical
that hematocrit be appropriate as well as cardiac output. If these determinants of O2
delivery are reduced, then that means that even with a marginally acceptable arterial
PO2, O2 delivery may not be sufficient. So what can you do for a baby that has inadequate
arterial delivery and saturations? Well, pretty much from regardless of the form of disease–
and this applies to lung disease as well as heart disease– there are a number of things
one can do to improve O2 delivery. One can optimize hematocrit. I don’t think
anybody knows precisely what the very most optimum adequate is for O2 delivery. But it
seems in general that hematocrit somewhere in the 45 range are probably pretty close. One can do one’s best to obtain adequate systemic
diffusion, appropriate volume infusion as needed, and inotropic agents can be very helpful.
Time does not permit a full discussion of these, but the general use of these agents
to improve cardiac output can be helpful in cyanotic patients. When we optimize a ventilation which oftentimes
will require means of mechanical ventilation, but not always, and can minimize total body
O2 consumption through the use of chemical paralysis, mechanical ventilation, sedation,
and temperature control. And finally, one can use therapy to reduce
or eliminate acidosis, make sure glucose and calcium levels are acceptable. Prostaglandin E1 is a definitive palliation,
although not permanent therapy for many lesions. It’s certainly necessary when there’s high
grade anatomic obstruction, pulmonary blood flow. As I noted, it’s often, but not always helpful
in the transposition. And as also noted, it can actually be harmful with obstructed total
anomalous pulmonary venous connection. Or in any case in which a systemic hypotension
may be non-helpful. It’s important to note that Prostoglandin
E1 is a systemic vasodilator. And when this medication is started, it’s oftentimes necessary
to use some degree of volume infusion, or even inotropic and alpha-adrenergic agents
in order to secure adequate blood pressure. One also needs to keep in mind that the Prostoglandin
E1 also can cause apnea. This is especially true in prematures. It also seems to have
an added effect along the sedation, so that babies that are sedated for procedures or
tests or more prone to apnea with Prostoglandin E1, and one needs to keep this in mind. Babies that are transported shortly after
an E1 has been initiated, or even for that matter a number of hours after it, because
sometimes the apnea that occurs with this medication occurs many hours later. One needs to consider whether or not this
patient should be intubated. Whether or not intubation is indicated in this situation
depends upon the exact circumstances, but one always needs to consider this before transporting
a patient. The dose that’s used to open a closed ductus
with E1 is 0.1 micrograms per kilogram per minute. For babies that already have opened
ductuses, and one wants to maintain patency, we use a much lower dose. We generally use
between 0.01 and 0.02 micrograms per kilogram per minute in order to maintain patency. As I noted before, it’s important if one wants
to avoid apnea to try to be ginger in one’s use of sedatives in patients on the Prostoglandins. There is also at least one paper in the literature
that would suggest that pre-treatment with aminophylline, and one presumes that caffeine
may have the same effect– it reduces the risk of apnea in babies with Prostoglandin
E1 substantially. Definitive palliation for babies mostly with
d-transposition of the great vessels– there are a few other unusual circumstances– but
primarily d-transposition of the great vessels is really affected by Rashkind Balloon Septostomy.
It’s performed by skilled personnel, generally well-trained pediatric cardiologists. It can
be done at the bedside using echocardiographic guidance or in the cath lab. There is a relatively low risk of complications
with this procedure, but the ones that do occur can be very serious. There is a risk
of air embolism because of the technical features of the way this is generally done. Also, some
risk of injury to systemic or pulmonary veins or AV valves. So it’s important that the hands performing
this procedure be skilled and experienced. Many babies that have this particular procedure,
by the way, still require an open ductus for adequate oxygen saturations. Simply having an open atrial septum does not
always ensure adequate mixing. This is an angiogram of a baby with d-transposition.
It has a Rashkind Balloon Septostomy and catheter placed in the left atrium. And the catheter
came up the inferior vena cava across the foraminal valley. And the balloon was inflated,
which by the way, has contrasts, radio-opaque contrasts, and it was inflated. And you see
the balloon is briefly advanced and then forcibly pulled across the atrial septum into the right
atrium, as illustrated here. Finally, I’ll just briefly mention that there
are a few unusual situations that you might wind up encountering that will require slightly
different therapy. There are a few, but not many patients with congenital heart lesions
that have increased pulmonary vascular resistance, much as is seen in persistent pulmonary hypotension
of the newborn. The only lesion in which this is seen with
any frequency– and even in this case– it’s unusual, but not unheard of, is d-transposition
of the great vessels. These babies occasionally have very high resistance,
which to some extent, is oftentimes responsive to inhaled nitric oxide or other vasodilators,
and tends to resolve after a few days. These patients may require nitric oxide or
even ECMO support in order to support them while their vascular resistance is falling
postnatally. Babies with congenital heart disease that
have persistent findings of significantly elevated pulmonary vascular systems are quite
uncommon, and make one think of the possibility of alveolar capillary dysplasia, which has
been described in a number of congenital heart patients, especially left-side obstructive
lesions. Some babies with right-side obstructive lesions,
especially a Tetralogy of Fallot, will have a congenital absence of the ductus arteriosus. If the baby has no ductus and severe outflow
tract obstruction, Prostoglandin E1 will not be of any use in palliation, of course. These patients can be treated sometimes palliated
for some period of time by increasing their systemic vascular resistance so as to effectively
force blood across the high-grade obstruction in the right ventricular outflow tract. Phenylephrine
is most typically used for this. ECMO support can be useful. Sometimes these
babies can be treated in the Cath lab by placement of a stent out the right ventricular outflow
tract in order to open this up sufficiently for adequate PO2s. Patients with obstruction of the total anomalous
pulmonary venous– anomalously connected pulmonary veins require emergency surgery because there’s
really no effective form of palliation other than very short-term ECMO under unusual circumstances. So, by and large, these patients require prompt
diagnosis and prompt definitive surgical therapy. Finally, to finish up the lecture, I’d just
like to spend a few minutes talking about ICU therapy for patients with single ventricle
physiology and unobstructed pulmonary blood flow. Patients with this combination of defects
tend to develop over the first few postnatal days. Excessive pulmonary blood flow– and
reason is, of course, this is normally a resistance to blood flow through the lungs is much lower
than the body. And as pulmonary resistance falls– and it tends to fall quite rapidly
after birth– these patients actually tend to send more and more blood to the lungs and
less blood to the body. Since the heart can only pump out a total
amount of blood– a volume of blood at any one time, these patients tend to have only
mild hypoxemia, their saturations are in the 80s or even 90s. And there is a tendency for
systemic bloodflow to be reduced due to the excessive bloodflow into the lungs. Typical lesions that have this or truncus
arteriosus– generally, in most cases– do not have obstruction of the pulmonary arteries,
hypoplastic left heart, or any single ventricle defect with unobstructed total pulmonary bloodflow. This is a slide that I had shown in the previous
part 1 lecture that relates the total amount of pulmonary to systemic flow of the QP to
QS to oxygen delivery. As you may recall from the first lecture,
as QP to QS goes up beyond a certain level, the blood that goes to the lungs effectively
is blood that’s stolen from the body. Given the fact the heart can only pump so much blood,
and as a result, the total amount of O2 delivery– which is of course dependent upon not only
arterial saturation, but also systemic blood flow– tends to go down. These are computer-generated curves of the
late QP to QS systemic O2 availability which is the same as delivery. And what it shows–
and I put a red circle on the graph to indicate the amount of total cardiac output that most
neonates generally have. And as the QP to QS goes much more than a little bit less than
1, the total O2 delivery to the body actually falls even as the arterial saturation goes
up. So it’s important that these patients be managed
in such a way that the natural tendency to have too much pulmonary bloodflow is not encouraged.
And the way we do that is we avoid therapy that decreases pulmonary resistance, we avoid
hyperoxia and alkalosis, both of which tend to vasodilate the lungs a pulmonary vascular
bed. We avoid systemic hypertension. As systemic
vascular resistance goes up, this tends to force more blood into the low resistance pulmonary
circuit. Patients like this may also benefit somewhat
from inotropic support in order to maximize a cardiac output. Diuretics can be helpful
since they tend to accumulate some fluid in their body and their lungs. An occasional patient may benefit from sub-ambient
oxygen, FiO2 in the 15-16 range or so. If in fact they show signs in decreased systemic
perfusion we actually don’t tend to use that very much in our institution, but under certain
closely monitored circumstances it may be helpful. Summary. So to summarize, it’s important to
identify cyanotic lesions that seem likely to have congenital heart disease so that prompt
diagnosis can be undertaken. One can certainly base diagnosis as best as
possible on– or base therapy– as best as possible on specific diagnoses. And prostaglandin
E1 when used appropriately can be very helpful. Even before one has a specific diagnosis,
I should emphasize that for severely hypoxemic patients, generally speaking, the likelihood
is greater that you will help than harm the patient with prostaglandin E1. So especially
if one is dealing with life threatening hypoxemia, waiting for a specific diagnosis to initiate
prostaglandin E1 would generally not be the appropriate thing to do. If the baby, upon being started on prostaglandin
E1 becomes hypotensive or more hypoxemic, one may need to modify that therapy. But one
should be relatively liberal in one’s use of prostaglandin E1, absent specific contraindications. And finally, and this is a very important
important point, some therapy, for example, optimizing hematocrit, minimizing O2 consumption,
and promoting adequate systemic blood flow is helpful for just about anybody with severe
hypoxemia and can be applied even when there isn’t a specific diagnosis while one is waiting
to do that. Thank you very much. Please help us improve the content by providing
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