cyanotic congenital cardiac defects: diagnosisand therapy, by doctor tom kulik. i'm doctor tom kulik. i'm a pediatric cardiologistand cardiac intensivist at the children's hospital, boston. this lecture will be thesecond part of two lectures in regards to the diagnosis and management of the infantwith cyanosis. introduction. to briefly preview the lecture, we will firstreview 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 importanttypes 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 surgicalpalliation, or surgical correction of these lesions, but rather focus on the sort of thingsthat the neonatologist and intensivist will be involved with in their unit-- stabilizingand preparing the baby for more definitive treatment. physiology. let's briefly talk about the physiologyof cyanosis caused by congenital heart defects and review material that we had previouslydiscussed. 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 withtetralogy of fallot. in this case, there was a ventricular septal defect and outflow obstructionbetween the right ventricle and pulmonary
artery. hence, blood tends to go right toleft across the vsd into the aorta. right to left, interatrial shunting. in thiscase, it's a baby that has severe pulmonary stenosis. the obstruction to blood flow fromthe right ventricle to the pulmonary artery is so severe that an entire cardiac outputcannot be injected into the lungs, and hence, there's a considerable amount of right toleft shunting at the atrial level, not ventricular level. let's talk about what i might termsimple, or perhaps more commonly termed, complete mixing. and what you see here is an exampleof 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 bloodwith red pulmonary venous blood. and as a
result, there is a cyanosis. and finally, transposition physiology is thephysiology that occurs in babies that have a d-transposition of the great vessels. thatis to say the aorta is attached to the right ventricle and the pulmonary artery to theleft ventricle. in which case, there tend to be two separate circuits whereby the blueblood 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 surviveex-utero by virtue of some degree of mixing of the red and blue streams. and we will discussthis a little bit more in just a few minutes. there are multiple determinants of arterialoxygen saturation in congenital heart disease.
they can pretty much be boiled down to thesefive factors. the first is pulmonary venous oxygen saturation. obviously, a baby withcongenital heart lesion will be bluer than he or she would otherwise be if there is lungdisease, and hence, the pulmonary venous blood is not fully saturated. the ratio of pulmonaryto systemic blood flow, also known as qp:qs, is very important in babies with either completemixing lesions, or even a simple right to left shunting. the amount of systemic bloodflow, the hemoglobin content of the blood, and the total body o2 consumption are alsoimportant in determining arterial oxygen saturation. and the reason for this is that whenever thereis 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 blueblood is, the less red the arterial blood will be as it's ejected from the heart. soas systemic blood flow falls, mixed venous oxygen saturations also tend to fall. withless o2 delivery to the body because of lower hemoglobin, the mixed venous o2 saturationtends to fall. and as more oxygen is extracted because of high oxygen consumption, that alsotends to negatively impact the oxygen saturation of the venous blood. so these are the key determinants of arterialo2 saturation in just about any congenital heart lesion. perhaps the only exception tothat is d-transposition of the great arteries. and there, the key issue is how much mixingof the red blood and the blue blood streams
occurs. and again, we'll talk about this abit 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 congenitalheart disease from lung disease and persistent pulmonary hypertension of the newborn. we'renot going to try to provide enough information to allow one to make a specific diagnosisof a heart defect without performing an echocardiogram, because echo is really the definitive waywe make these diagnoses in the vast majority of cases. so i'm going to emphasize for thenext few minutes the things that one can observe in a baby in terms of physical signs and symptomsthat make one most concerned about the possibility
of a congenital defect, and hence initiatingprompt detailed evaluation of such. so let's talk about these red flags for congenitalheart disease. the first is babies that are cyanosis with what one of the kind of foundingfathers of pediatric cardiology, alex nadas, termed "happy tachypnea." happy tachypneais tachypnea without dyspnea, or a baby who's breathing fast but very easily. babies withlung 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 compliantlungs, and hence, although they will be tachypnic because of a hypoxic respiratory drive, theydon't tend to breathe particularly hard. and so happy tachypnea tends to make one thinkmore of heart disease and less of lung disease.
now, one has to be careful though. there isa 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 betweentheir origin and the heart, these babies can develop very severe pulmonary edema as isillustrated on this chest x-ray of a young patient with total obstructed veins. and thesebabies will have a considerable amount of dyspnea. so one always has to keep obstructivetotal veins in mind when presented with the cyanotic baby that has a lung finding suggestiveof pulmonary edema. the second red flag for congenital heart diseaseis differential cyanosis. differential cyanosis is when the oxygen saturations are differentin the right arm versus the lower body. and
there are basically two types of differentialcyanosis. the first is differential cyanosis due to right to left shunting of systemicvenous blood into the descending aorta. this can occur under two circumstances. one is persistent pulmonary hypertension ofthe 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 shuntblood from the pulmonary artery into the descending aorta, such that their oxygen saturationsin their right arm will be considerably higher than in their legs. not all babies with pphnhave differential cyanosis, but certainly many of them do.
those same findings however, can occur inbabies with congenital heart lesions. for example, i've shown a baby with interruptionof the aortic arch. in this particular set of circumstances, all of the profusion tothe lower body is via the right ventricle across the ductus and so these kids will tendto have substantially lower oxygen saturation in the lower extremities than in the rightarm. so differential cyanosis, while it can occur without a congenital heart lesion, specificallywith pphn, can also occur with certain forms of heart disease. the second flavor, if you will, of differentialcyanosis is reverse differential cyanosis. and with reverse differential cyanosis, theoxygen saturations are actually higher in
the lower body than in the right arm. andwhere this is occasionally seen, and i think pretty much the only time it's occasionallyseen, is in babies with d-transposition of the great vessels or a very similar anatomiclesion. in this case, if there is very high resistanceto blood flow in the lungs, and there's a patent ductus arteriosis, when the left ventricleejects blood into the pulmonary artery, a certain fraction of it will tend to go acrossthe ductus into the descending aorta. since this is red pulmonary venous blood, thesepatients will actually tend to have higher oxygen saturation in the legs than in theright arm. this can occur either because, as i just mentioned, high pulmonary vascularresistance, or sometimes coarctation of the
aorta in a d-transposition, where there isnarrowing of the isthmus of the aorta, the segment between the left subclavian arteryand the ductus. and that can also give reverse differential cyanosis. so the finding of reversedifferential cyanosis is very highly suggestive of congenital heart disease. murmurs can constitute a third red flag forcongenital heart disease. as i think most folks know, very soft murmurs are very commonin babies, and grade one to two over six murmurs do not necessarily connote congenital heartdisease. on the other hand, murmurs of grade three intensity or louder are quite unusualin otherwise normal babies, and certainly raise a red flag in a baby who has lower thannormal arterial oxygen saturations. continuous
murmurs in the back are also very uncommonin otherwise normal newborns and make one think of a lesion like tetrology of fallotwith pulmonary atresia. and there is one murmur in particular, thatis to say, the to and fro, not so much continuous, but to and fro murmur at the left upper sternalborder, 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 situationsin which a typical to and fro murmur like this is heard. so murmurs can sometimes putone on the alert for congenital heart lesion. point number four refers to the so-calledhyperoxia test, that is to say if one gives a baby with lung disease a very high inspiredoxygen, generally the po2 will go up substantially
or the o2 sat goes up substantially by virtueof the fact that most babies that are cyanotic by virtue of lung disease have vq mismatchas a primary cause for this. and this is quite responsive to oxygen. one can read variouscut-off levels for arterial po2 in response to 100% oxygen as discriminating between congenitalheart disease and lung lesions. i've used po2 of 200, because it's certainly possiblefor 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 notincrease their arterial po2s that much on 100% oxygen. on the other hand, babies withcertain forms of heart disease, for example,
total anomolous pulmonary venous connectionbelow the diaphragm will occasionally have streaming pulmonary venous blood in such away 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 itwould be safe to say that any po2s less than 200 or even somewhat greater than that, wouldmake one have to consider the possibility of congenital heart defects. and in fact, probably a more sophisticatedway to think about this, although a non-quantitative way, is to consider that whenever the arterialpo2 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 becautious. babies with obstructed total anomalous pulmonary venous connection can have verywet appearing chest x-ray, which might imply pneumonia, but in fact, is pulmonary edemadue to their congenital heart lesion. electrocardiogram is generally normal in mostbabies 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 zerodoes 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 deviationoccurs. finally the chest x-ray can be helpful. certainlydextrocardia doesn't prove the presence of
congenital heart disease although it makesquite likely. midline stomach bubble, as one sees with hetrotaxy syndromes also markedlyincreases the likelihood of congenital heart disease. right aortic arch can be a findingin a normal person, but it also suggests the possibility of tetralogy of fallot, truncusarteriosus or transposition views to pulmonary stenosis. and a classic finding with babiesthat have tetralogy of fallot or tetrolagy of fallot with pulmonary atresia is the upturnedcardiac apex combined with the flat pulmonary arterial segment on the chest x-ray and rightaortic 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 physicalfindings that make one concerned about heart disease, let's talk about the specific typesof cyanotic heart disease that occur most often in babies with this lesion. we're notgoing to go over detailed descriptions, but i hope to provide enough information thatyou'll have a general idea of what you will be dealing with about 99% of the time whendealing with cyanotic infants. and i'd like to break these lesions down intowhat you might call a ductus-centric classification. that is to say, categorize the babies, thepatients, 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-1may not be either required or even helpful. the third type of classification are babieswith 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 connectionwith obstruction. in those cases, babies neither benefit from-- in fact, they actually havea 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 e1is required therapy. the first would be babies with critical pulmonary stenosis or pulmonaryatresia. as i mentioned earlier in this lecture, babies with this particular lesion have sucha 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 thelungs. and hence, there is a very large amount of right-left shunting at atrial level. there'sa 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 rightventricle, but with relatively heavy trabeculations due to hypertrophy that's occurred in uterobecause of the very high right ventricular pressure. and you see a very thickened pulmonaryvalve. ordinarily, you can't really see the pulmonaryvalve very well on angiography and with a relatively small jet of contrast that goesacross 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 theductus is critical. tetralogy of fallot, if severe enough, canpresent with life-threatening hypoxemia in a neonate because of a marked reduction inpulmonary flow. i want to make the strong point, however, that most babies with tetralogyafter they're born, do not have severe obstruction to right ventricular outflow. most neonataltretralogies have quite adequate oxygen saturations without an open ductus, and really requirevery 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 thesame physiology. babies with single ventricle lesions thathave 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 thereis basically no right ventricle, no tricuspid valve. and so systemic used blood goes fromthe 2 cava into the right atrium, crosses the atrial septum into the left atrium andmixes with pulmonary venous blood there, enters the left ventricle, some is ejected into theaorta. and then some finds its way into the lungs, presuming there is an open vsd in asub-pulmonary chamber. if the vsd is quite restrictive, or the areaunderneath the pulmonary artery is quite narrow,
there may be a critical reduction in pulmonaryblood flow. in which case, prostaglandin e1 won't be required. now, not all tricuspidatresia babies have this critical reduction. some do not require prostaglandins. but somedo. and this is true for other single ventricle defects that have restricted pulmonary bloodflow. finally, this is a rare lesion. even largecenters will see this only a very few times of the year. but it's worth mentioning. ebstein's malformation basically is when thetricuspid valve is displaced into the right ventricle such the right ventricular massis reduced in functional volume. and the valve itself is very nonfunctional. so it tendsto have marked regurgitation.
there's a whole spectrum of ebstein's. verymild ebstein's is consistent with an asymptomatic long life. very severe ebstein's shows upin the way i've illustrated on this screen, with a baby that has a massively dilated heartin utero and immediately ex-utero and a right ventricle that by virtue of the tricuspidregurgitation, is basically insufficient to eject blood out the pulmonary artery and intothe lungs. these babies require an open ductus in order to provide adequate pulmonary bloodflow. the second general category of patients withcyanotic heart disease are those that have little or no obstruction to pulmonary bloodflow 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 ventricularoutflow obstruction. and so this would generally be the case for most babies with tetralogy. babies with tetralogy of fallot and so-calledmapcas, or multiple aortopulmonary arteries, are patients that also oftentimes do not requireprostaglandin for palliation. babies with this particular lesion are like tetralogyin 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 connectionbetween right ventricle and the pulmonary arteries, there is no connection. and bloodfinds its way into the lungs either as through the so-called aortopulmonary collateral vesselsor, in some cases, through an ductus arteriosus.
babies that do not have a ductus arteriosusand has supply through the aortopulmonary collateral vessels, of course, are not ductiledependent. i've illustrated the angiogram on the right side of the slide as arrows pointingto these collaterals that come directly of the aorta. these babies are not prostaglandindependent. do hasten, however, to make note of the fact that some subset of babies withtetralogy of fallot and pulmonary atresia will basically have their entire pulmonaryblood 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 requireprostaglandin e1 unless there is some additional lesion such as interruption of the aorticarch. babies with truncus basically have two
normal-sized ventricles and a vsd. and thenthere's a single large vessel that arises from these two ventricles this gives riseto both the aorta and pulmonary arteries. and this is not a ductile-dependent form ofcyanotic heart disease. babies with single ventricle lesions that have no obstructionto pulmonary blood flow do not require prostaglandin e1 in order to maintain adequate pulmonaryblood flow. now i hasten to make note of the fact thatsome of these babies can have obstruction to their aorta, either flow from the ventricleinto the aorta or coarctation or other narrowing of the aorta. in that case, prostaglandine1 may be required. but simply talking about babies with cyanotic defects, if there isno obstruction to pulmonary blood flow in
a single ventricle patient, there is no needfor a prostaglandin e1 in order to maintain adequate pulmonary blood flow. in the case of babies with transposition ofthe great arteries, prostaglandin e1 may be helpful. as you recall, these babies requiremixing of the red and blue blood streams in order to provide adequate 02 delivery to thebody. this generally has to, at least in part, occur at the level of the atrial septum. mixingat the level of the ductus as a sole level of mixing is not adequate. but the presence of an open ductus can increasepulmonary blood flow and augment mixing of the atrial level. and so for that, using prostaglandine1 may be helpful in babies with transposition.
not all babies will adequately respond tothis, however. there is an occasional baby with d-transpositionthat actually becomes acutely ill after introduction of this medication for whatever reason. soone has to keep this in mind. but by and large, maintaining ductile patency is helpful inthese patients with transposition. babies with total anomalous pulmonary venousconnection, on the other hand, may actually be harmed by prostaglandin e1. if these babieshave obstruction to pulmonary venous return to the heart, the resistance to blood flowthrough the lungs is very high. in which case, if the ductus arteriosus is open, blood that'sejected 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 therapythat's available for patients that are hypoxemic? well, basically there are three things thatone needs to do in order to effectively apply this therapy. the first thing is to assessand 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-threateninghypoxemia. and by the way to measure arterial oxygen saturations or po2s. transcutaniousoximeters are really not very accurate when
the oxygen saturation is low and really aren'tacceptable in many cases for determining whether a baby is seriously hypoxemic or merely hasa lower than normal oxygen level. it's necessary to make ultimately an accuratediagnosis 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 withoutsurgery. so what is life-threatening hypoxemia? atleast 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 onlyin terms of arterial saturation, but o2 delivery to the tissues.
o2 delivery-- the equation describes oxygendelivery to the tissues-- is very simple. it's basically delivery equals content ofarterial 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 normalheart-- 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 thata non-elevated lactate level necessarily implies that all organs, especially the brain, haveadequate o2 delivery. but as a general index of total o2 delivery sufficiency, a lack ofhigh lactates tends to be a somewhat reassuring. in general, i think one could say that withacceptable hemoglobin and cardiac output,
at least in newborn babies, arterial po2sin the low 20 range are tolerated at least for some period of time. and certainly, arterialpo2s of greater than 25 seem to be well tolerated for at least some period of hours or perhapseven longer. but again, i emphasize that it's criticalthat hematocrit be appropriate as well as cardiac output. if these determinants of o2delivery are reduced, then that means that even with a marginally acceptable arterialpo2, o2 delivery may not be sufficient. so what can you do for a baby that has inadequatearterial 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 thingsone can do to improve o2 delivery.
one can optimize hematocrit. i don't thinkanybody knows precisely what the very most optimum adequate is for o2 delivery. but itseems in general that hematocrit somewhere in the 45 range are probably pretty close. one can do one's best to obtain adequate systemicdiffusion, 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 agentsto improve cardiac output can be helpful in cyanotic patients. when we optimize a ventilation which oftentimeswill require means of mechanical ventilation, but not always, and can minimize total bodyo2 consumption through the use of chemical
paralysis, mechanical ventilation, sedation,and temperature control. and finally, one can use therapy to reduceor 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 highgrade anatomic obstruction, pulmonary blood flow. as i noted, it's often, but not always helpfulin the transposition. and as also noted, it can actually be harmful with obstructed totalanomalous pulmonary venous connection. or in any case in which a systemic hypotensionmay be non-helpful.
it's important to note that prostoglandine1 is a systemic vasodilator. and when this medication is started, it's oftentimes necessaryto use some degree of volume infusion, or even inotropic and alpha-adrenergic agentsin order to secure adequate blood pressure. one also needs to keep in mind that the prostoglandine1 also can cause apnea. this is especially true in prematures. it also seems to havean added effect along the sedation, so that babies that are sedated for procedures ortests or more prone to apnea with prostoglandin e1, and one needs to keep this in mind. babies that are transported shortly afteran e1 has been initiated, or even for that matter a number of hours after it, becausesometimes the apnea that occurs with this
medication occurs many hours later. one needs to consider whether or not thispatient should be intubated. whether or not intubation is indicated in this situationdepends upon the exact circumstances, but one always needs to consider this before transportinga patient. the dose that's used to open a closed ductuswith e1 is 0.1 micrograms per kilogram per minute. for babies that already have openedductuses, and one wants to maintain patency, we use a much lower dose. we generally usebetween 0.01 and 0.02 micrograms per kilogram per minute in order to maintain patency. as i noted before, it's important if one wantsto 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 literaturethat would suggest that pre-treatment with aminophylline, and one presumes that caffeinemay have the same effect-- it reduces the risk of apnea in babies with prostoglandine1 substantially. definitive palliation for babies mostly withd-transposition of the great vessels-- there are a few other unusual circumstances-- butprimarily 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 canbe done at the bedside using echocardiographic guidance or in the cath lab.
there is a relatively low risk of complicationswith this procedure, but the ones that do occur can be very serious. there is a riskof air embolism because of the technical features of the way this is generally done. also, somerisk of injury to systemic or pulmonary veins or av valves. so it's important that the hands performingthis 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 notalways 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 cathetercame 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 seethe balloon is briefly advanced and then forcibly pulled across the atrial septum into the rightatrium, as illustrated here. finally, i'll just briefly mention that thereare a few unusual situations that you might wind up encountering that will require slightlydifferent therapy. there are a few, but not many patients with congenital heart lesionsthat have increased pulmonary vascular resistance, much as is seen in persistent pulmonary hypotensionof the newborn. the only lesion in which this is seen withany frequency-- and even in this case-- it's
unusual, but not unheard of, is d-transpositionof 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 oreven ecmo support in order to support them while their vascular resistance is fallingpostnatally. babies with congenital heart disease thathave persistent findings of significantly elevated pulmonary vascular systems are quiteuncommon, and make one think of the possibility of alveolar capillary dysplasia, which hasbeen described in a number of congenital heart patients, especially left-side obstructivelesions.
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 outflowtract obstruction, prostoglandin e1 will not be of any use in palliation, of course. these patients can be treated sometimes palliatedfor some period of time by increasing their systemic vascular resistance so as to effectivelyforce blood across the high-grade obstruction in the right ventricular outflow tract. phenylephrineis most typically used for this. ecmo support can be useful. sometimes thesebabies can be treated in the cath lab by placement of a stent out the right ventricular outflowtract in order to open this up sufficiently
for adequate po2s. patients with obstruction of the total anomalouspulmonary venous-- anomalously connected pulmonary veins require emergency surgery because there'sreally no effective form of palliation other than very short-term ecmo under unusual circumstances. so, by and large, these patients require promptdiagnosis and prompt definitive surgical therapy. finally, to finish up the lecture, i'd justlike to spend a few minutes talking about icu therapy for patients with single ventriclephysiology and unobstructed pulmonary blood patients with this combination of defectstend to develop over the first few postnatal days. excessive pulmonary blood flow-- andreason is, of course, this is normally a resistance
to blood flow through the lungs is much lowerthan the body. and as pulmonary resistance falls-- and it tends to fall quite rapidlyafter birth-- these patients actually tend to send more and more blood to the lungs andless blood to the body. since the heart can only pump out a totalamount of blood-- a volume of blood at any one time, these patients tend to have onlymild hypoxemia, their saturations are in the 80s or even 90s. and there is a tendency forsystemic bloodflow to be reduced due to the excessive bloodflow into the lungs. typical lesions that have this or truncusarteriosus-- 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 previouspart 1 lecture that relates the total amount of pulmonary to systemic flow of the qp toqs 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 effectivelyis 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 onlyarterial saturation, but also systemic blood flow-- tends to go down. these are computer-generated curves of thelate 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 mostneonates generally have. and as the qp to qs goes much more than a little bit less than1, the total o2 delivery to the body actually falls even as the arterial saturation goesup. so it's important that these patients be managedin 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 avoidhyperoxia and alkalosis, both of which tend to vasodilate the lungs a pulmonary vascularbed. we avoid systemic hypertension. as systemicvascular resistance goes up, this tends to
force more blood into the low resistance pulmonarycircuit. patients like this may also benefit somewhatfrom inotropic support in order to maximize a cardiac output. diuretics can be helpfulsince they tend to accumulate some fluid in their body and their lungs. an occasional patient may benefit from sub-ambientoxygen, fio2 in the 15-16 range or so. if in fact they show signs in decreased systemicperfusion we actually don't tend to use that very much in our institution, but under certainclosely monitored circumstances it may be helpful. summary. so to summarize, it's important toidentify cyanotic lesions that seem likely
to have congenital heart disease so that promptdiagnosis can be undertaken. one can certainly base diagnosis as best aspossible on-- or base therapy-- as best as possible on specific diagnoses. and prostaglandine1 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 likelihoodis greater that you will help than harm the patient with prostaglandin e1. so especiallyif one is dealing with life threatening hypoxemia, waiting for a specific diagnosis to initiateprostaglandin e1 would generally not be the appropriate thing to do. if the baby, upon being started on prostaglandine1 becomes hypotensive or more hypoxemic,
one may need to modify that therapy. but oneshould be relatively liberal in one's use of prostaglandin e1, absent specific contraindications. and finally, and this is a very importantimportant point, some therapy, for example, optimizing hematocrit, minimizing o2 consumption,and promoting adequate systemic blood flow is helpful for just about anybody with severehypoxemia and can be applied even when there isn't a specific diagnosis while one is waitingto do that. thank you very much. please help us improve the content by providingus with some feedback.