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Congenital heart .docx

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NURS 203
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Congenital heart Know fetal circulation (which vessels have the least/most O ); rem2mber that the baby is NOT exchanging blood with O in 2he lungs. Pulmonary vessels in the fetus look like they have pulmonary HTN – they are so thick that it is extremely hard to get blood through the pulmonary artery into the LV b/c very little blood can go there – this is why baby needs a patent ductus to get blood out. Where is O com2ng from? Coming from chorionic villus dipping into lake of blood, which derives from mom’s spiral arterioles. Have chorionic villi dipping into blood and extracting O 2rom it. Obviously, this is not as good an O sour2e as the lungs; therefore, you want a high affinity Hb to be able to get what little O is2down in the area – this is why babies have HbF, b/c of its high affinity to grab O from the blood. Bad news is that it gets the O , but 2 2 doesn’t want to give it up (says mine) – it left shifts the curve. What is compensatory response? This left shift causes tissue hypoxia, which will cause EPO to be released and the kid will have an 18 gram Hb – b/c of this, all newborns (in a sense) have polycythemia. This is the way around HbF’s high affinity for O 2 more RBC’s made, more Hb, and baby gets more O . 2 Order of O p2ssing: O goes2through syncytiotrophoblast of chorionic villus, into the cytotrophoblast, then through the myxomatous stroma of the chorionic villus, then into the blood vessel. The blood vessels of the chorionic villis all coalesce to form the umbilical vein. This has the highest O c2ntent. It goes to the liver and it can go two ways: 1) into the hepatic sinusoids and recollects into the hepatic vein and gets dumped into the IVC; and 2) ductus venosis and straight into the IVC. Then it goes up the right side of the heart; the foramen ovale is open in all fetuses (its not closed) – so all this blood is coming up the IVC – will it go straight across, through the foramen ovale and into the left atrium, or will it go into the IVC into the right atrium, down to through the tricuspid valve, and into the right ventricle? It will go through the foramen ovale. So, all this oxygenated blood will go directly from the right atrium of the foramen ovale into the left atrium, then the left ventricle and out the aorta. What about SVC blood valve? It is coming from the superior part of the right atrium (its not gonna make a left turn and go through the foramen ovale). It will go straight down, through the tricuspid valve into the right ventricle. Now, it will go out the pulmonary artery. This is a PROBLEM b/c the pulmonary vessels are too thick and it’s encountering this tremendous amount of pressure. To counter this problem, kept the patent ductus open (which is kept open by the PGE2, a vasodilator, made by the placenta) – so, there is a right to left shunt and blood can get out of the pulmonary artery and dumped back into the aorta. Then, when the baby is born and takes its first breath, the pulmonary vessels (that were all shut), all open within a millisecond, and blood is going through those pulmonary arteries and gas exchange is occurring through the lungs in literally seconds. Also, the patent ductus closes and forms the ligamentum arteriosum. This is normal fetal circulation. Vessels with the least O ar2 the 2 umbilical arteries, and the one with the most amount of O is th2 umbilical vein. Shunts: Look at O 2aturations (this is how they dx them – they catheterize, measure O saturati2ns in different chambers, and know which direction the shunts are going. Need to get used to two terms – step up and step down. If you have a left to right shunt, and have oxygenated blood going into unO ’d 2lood, what is happening to O s2turation on the right side? Step up b/c mixing O ’d wi2h unO ’d blo2d. If you have a right to left shunt with unO 2d blood going into the O ’d2blood? Step down. The O 2aturation on the right side of the heart in blood returning from the body is 75%. The O 2 saturation on the left side is 95%. VSD (MC) Who’s stronger - left or right ventricle? Left, therefore the direction of the shunt is left to right. So, oxygenated blood will be dumped into the right ventricle, leading to step up. Also, it will pump it out of the pulmonary artery, leading to step up. So, you have a step up of O in r2ght vent and pul artery. What if this is not corrected? With this mech, you are volume overloading the right side of the heart b/c of all that blood coming over. The outcome of this will be pulmonary HTN (the pulmonary artery has to deal with more blood and must contract more – leading to pul HTN) – Once pul HTN occurs, right ventricle will have a problem contracting and it will get hypertrophied. Suddenly, you run the risk of reversing a shunt b/c then right ventricle could eventually be stronger than the left. So, it will be a right to left shunt – this is called Eisenmenger’s syndrome. So, an uncorrected left to right shunt has the potential for producing Eisenmenger’s syndrome. After reversal of the shunt occurs, pt will have cyanosis (aka cyanosis tardive). Most VSD’s close spontaneously and some need to be patched. ASD Normal for a fetus to have a patent foramen ovale; it is not normal once they are born. Which direction will blood go through the foramen ovale? Left to right (b/c the left side is always stronger than the right). Therefore, what will happen to the right atrium? Step up – so it will go from 75 to 80%. What will happen to the right ventricle and pulmonary artery? Step up. So, what is the main diff in O2 saturations in VSD vs ASD? ASD is step up of O2 also in the right atrium. Are you volume overloading the right heart? Yes. So do you run a risk for Eisenmenger’s? Yes. What else are at increased risk for? Paradoxical embolization. What if you weren’t lucky enough to have a DVT in the leg, and it embolize up and the pressures of the right side of the heart are increasing, and you have a patent foramen ovale – will there be an embolus that can go from the right atrium to the left atrium and will have a venous clot in arterial circulation? Yes – this occurs in pts with ASD. MC teratogen that has ASD associated with it? Fetal alcohol syndrome (1/5000) PDA It’s normal in a fetus but not when they are born. Connection between the aorta and pulmonary artery – which is stronger? Aorta. So, oxygenated blood goes from left and get dumped in the pulmonary artery before going into the lungs. So, what happens in the pulmonary artery? Step up. So, now its 80% O2 saturation – the pulmonary artery is the only thing that has a step up of O2. Then will go under the lungs and the pulmonary vein will have the normal 95% O2 sat. B/c there is an opening between these, there is blood going back and forth during systole and diastole – machinery murmur – where is it heard best? Between shoulder blades. Can you vol. overload the right heart? Yes. Pulmonary HTN? Yes. Now which way will the shunt go? Will go the same way when it was a fetus; you will have unO2’d blood dumping into the aorta. Where does the ductus empty? Distal to the subclavian artery – so, the baby will have pink on top and blue on bottom b/c dumping unO2’d blood below the subclavi
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