Feb 20, 2018
Dr. Roberta Keller is a neonatologist, an expert in caring for critically ill newborns, particularly those with congenital lung or heart disease. She is director of the USCF Benioff Children’s Hospital Extracorporeal Membrane Oxygenation (ECMO) program, or artificial lung, for newborns. Her research addresses lung and heart disorders affecting newborns, such as congenital diaphragmatic hernia and patent ductus arteriosus. In this episode, Dr. Keller discusses the basics of neonatology.
I'm Dr. Robert Keller. I work at the University of California at San Francisco, the Benioff Children's Hospital. My specialty is neonatology, which is newborn intensive care. My area of focus is newborn lung disease, and pulmonary vascular disease, and lung disease leading to chronic problems with pulmonary hypertension.
Neonatology is newborn intensive care. We take care of babies who are sick from birth. Many times, that means babies who are born preterm. They need intensive care from the time of birth due to their small size and underdeveloped lungs and organ systems, to help support their breathing, their gas exchange, but also to help feed them safely and get them nourished, and growing, and get them to the point that they can come off that support.
In addition, there's a large population of babies we take care of who are born with birth defects that require, again, intensive care. The ones that I focus on are ones that affect the development of the lungs. A baby with diaphragmatic hernia who's born at term on time can have the size of lungs of a baby who weights 1,000 grams, which is two pounds. Even though they're born at a normal size, they have very tiny lungs that are underdeveloped. They don't function well. They don't exchange gas well. On top of that, the pulmonary vascular bed is underdeveloped. It causes circulatory compromise along with the impaired gas exchange. The things that we focus on, again, are these children who are born very early but also children who are born with birth defects who require supportive care in order to get to the point that they can breathe on their own, eat on their own, and get adequately nourished.
What we see normally when babies are born healthy with normally developed lungs is that they have, when they're in utero, inside the mother, they have a relatively high pulmonary vascular resistance. Their blood vessels in their lungs are developed normally, but they're somewhat constricted in the normal fetal circulation, because blood flow to the lungs is decreased compared to what it needs to be once you're exchanging gas through your lungs. The lungs are a growing organ, but they're not functioning for gas exchange. The placenta does that so that you exchange gas from your mother, and that's how the fetus gets oxygenated and is able to clear its carbon dioxide.
What happens at birth when a healthy baby first cries and takes that big breath that everyone likes to hear and gets excited about is their lungs open up. As the oxygen comes in, so they've been in a very low-oxygen environment, now they're breathing room air, but that's already more oxygen than they were exposed to. As the oxygen comes in and the lungs open up, those blood vessels relax and dilate, and a bunch more blood flow starts going through the lungs. Within 24 hours, you have the same amount of blood flow going through the lungs that you have going to the body.
Babies who are born with birth defects that affect their lung development, the blood vessels to the lung, there's fewer of them. It's a smaller vascular bed. When they get that relaxation, there's just not as much area for the blood to travel through. Then sometimes also those blood vessels don't relax in the usual way. They don't go through that normal transition in the first 24 hours, and in fact, have a very delayed transition. Many of them are born with pulmonary hypertension.
Now what we've shown in some of the work we've done with congenital diaphragmatic hernia by following these very sick babies with serial echocardiograms is most of the babies who do well actually transition at least by echocardiogram around between two and three weeks of age, somewhere in that range. As opposed to the first two to three days of age, they're transition is delayed to two to three weeks of age. Those children who do well are still able to transition. It's just a very delayed transition. During that period of time, they have some degree of pulmonary hypertension.
Then, there's a proportion of kids who don't transition. They get up to that two to three week of age, and they still have quite significant pulmonary hypertension. Those are the children I think that we really need to focus on. Some of the recommendations we had in the [Pediatric Pulmonary Hypertension] guidelines are focused on that group of kids. Some of the recommendations in the guidelines, they're focused on not doing harmful things. Yes, we know they have pulmonary hypertension, but we also know they have small lungs that are vulnerable to injury. Let's be judicious in the support we give. Let's give them enough support but maybe calibrate our expectations as to what enough support is, and really try and not harm things, and allow that transition to happen, even though it's going to be delayed to two to three weeks of age instead of by two to three days of age. If some of the recommendations and the guidelines are really focused on that, let's allows that to happen, and by not harming things and causing that to be delayed and causing more problems.
But then some of the other recommendations are focused around then what happens when you don't make that transition and those children who really have much more problems with persistence of pulmonary hypertension and maybe even some changes in their pulmonary vasculature that they're starting to really have more pulmonary vascular disease. The recommendations we've made there are, one is try and preserve right heart function. The right heart is the dominant ventricle in utero. It knows how to work by allowing it to not have to pump always against the pulmonary circulation if that is a very constricted, small, vascular bed, by keeping the ductus arteriosus, which is a normal vessel inside the uterus in fetal life, by allowing that to stay open, allowing the right ventricle to have that and maintain that fetal circulation, we can protect to some extent the right heart function while we're allowing for that delayed transition in those babies who take longer than two to three weeks.
Then for those kids who really fail to even transition by four to six weeks of age, thinking about evaluating them in the same way we evaluate any children who we're concerned about chronic pulmonary hypertension and really making sure we get the information we need to think about the types of treatments they might need long term.
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