Wednesday, May 12, 2010

35 Wks, 2 Days: Hoping for Lots of Bubbles

This is so bizarre: the very career-oriented respiratory therapist waiting on a test to determine lung maturity. My amnio is at 1:30 this afternoon, and I, as usual, cannot sleep. This is essentially where the rubber meets the road- what I have been gearing towards since January 29th, when I was first hospitalized for preterm labor at 20 weeks.

I have been talkng incessantly about it, but then realized that the layperson may not realize what all of the fuss is about. We all know that the lungs are the last to mature in a fetus. Lung development actually takes place in 2 stages. First, Baby Zachary had to produce all of his tiny little alveoli and his bronchiole tree. All of the exchange of carbon dioxide and oxygen occurs through a very thin membrane called the alveolar-capillary membrane. A single alveolus is very small-not much surface area for this exchange to happen. In its beauty of organization, his body has grown a ton of these little grape-like clusters of alveoli. More of them means more surface area for the all-important exchange vital for life outside of the womb, when my body will no longer be taking this role over for him. But that simply is not enough.

The second stage is the production of surfactant. What in the hell is that? Well, it is a slick, soap-like substance that lines and lubricates these alveoli. We all make it via these cells called Type II Alveolar cells. We see pathophysiology in adults, even, when the surfactant in their lungs is depleted. Without it, we can compare breathing to inflating balloons. No regular balloons either. Think of those teensy, tiny balloons you use to make fill with water for a water-balloon fight. And you blow and blow into the balloon, about to pop a blood vessel in your forehead trying to inflate them. That is essentially what it is like to try to breathe and inflate all of these little tiny alveoli without surfactant. So the surfactant acts to reduce surface tension, making this job easier. Once they are inflated, the body also does something else to make it easier--the functional residual capacity of the lungs. Basically, with each breath we take, a small amount of air remains in the alveoli after exhalation. Just like it is easier to inflate the tiny balloon once there is a small amount of air in it, it is also easier to breathe with the FRC.

A newborn's first breath is vital, and is also the most difficult, stressful event of his birth. Because after this development takes place, he "breathes" amniotic fluid to practice. This is how they are able to determine lung maturity from a sample of amniotic fluid. There will literally be traces of what is in his lungs in the actual fluid they withdraw from my belly via a very large needle poked through all of the layers of my belly, my uterus, and into the amniotic sac. If adequate surfactant is present, agitating the sample will produce bubbles like soap will, and we know that the cells in his lungs are working. (It's actually a little more complicated, as they actually send the sample to be chemically analyzed.) So when a baby is born vaginally, the process of childbirth actually squeezes this fluid out. Obviously, with a c-section, this doesn't occur, and often the baby will require invasive suctioning. Then his work begins. It takes an astounding amount of pressure to take that first breath. Even with the help of surfactant, his little body still has to generate enough negative pressure to pull in that first breath, overcoming the remaining fluid in his lungs and the collapsed alveoli. Once accomplished, the air literally pushes out the remaining traces of fluid in the alveoli, through the alveolar-capillary membrane, and ultimately into the his lymphatic system to be carried away.

In the meantime, a fetus's circulatory sytem is still geared to life in the womb. Our bodies, as adults, are designed to do all of the work for us. We filter our own blood. It goes in and out through different circuits, because it has to first go through the pulmonry circuit to be oxygenated by the lungs and rid itself of carbon dioxide before it can go through the remainder of the body to oxygenate the rest of the body tissues. For months and months, a fetus has had this role performed for him by Mom. In a portrait of efficiency, as a result, the fetus's body has these shunts in place. There are several--the Foramen Ovale, the Ductus Areteriosus, the Ductus Venosus--all designed to bypass the organs in his body that are not yet needed while in the womb.

Ever read about or talked to someone with a preemie who had a "PDA"? That is a Patent Ductus Arteriosus. Basically, birth is what we in healthcare call a "hypoxic event".The baby isn't breathing while he makes his transition to life outside of the womb in those first seconds. Without breathing and exchanging gases, the concentration of oxygen in his blood drops and the concentration of carbon dioxide increases. This shift in concentration causes changes in the pressures in his blood vessels, which triggers all of those shunts to close so his circulatory system can switch to that of an adult. In a PDA, this fails to occur.

So there you have it--a primer on what took years of college for me to learn, summed up in one little blog post, off the top of my head. Of course it has also been years since I have studied perinatal pulmonary development. But this is what we are waiting for so anxiously. This is why the biggest problem with a premature baby is usually respiratory in nature. Without proper time to "cook", the baby's lungs just aren't ready to do this on his own, which usually means intubation and machines doing it for him while his lungs finish developing. Then failure of the lungs to do this work results in a failure on the part of circulation to close all of the shunts. A steep, slippery slope.

Of course we have the tecnology to do a lot of this. We even have artificial surfactant we give. The biggest brand name is Survanta. We simply administer it through the endotracheal tube once the baby has been successfully intubated. Then we literally tip and tilt the baby around to make sure it gets to as many of those alveoli as possible. Picture greasing a cake pan. You pour a bit of oil into the pan, then tip and tap it around until it has covered the entire surface. We literally do the same thing with these tiny babies. But no matter what we can do artificially, nothing is as good as the Real Thing, like Mother Nature intended. Being on a ventilator opens the baby up for a host of complications. As with anything invasive,there is the risk of infection. There is the risk of damaging the tiny, fragile lungs with too much pressure or volume. There is a risk of pneumonia.

Knowing all of this has been my greatest strength and my greatest weakness throughout this horrendous pregnancy. I know exactly what can go wrong, making it even scarier for me. But I also know what we can do for the preemie outside of the womb, making it all the more harder to endure to give Zachary more time. When one has been a part of the successful resuscitation of a preemie so many times, and you see these babies go home with their families, it gets hard to picture any other result for your own child, and each painful contraction gets harder to endure.

I am almost positive Baby Zachary is ready. The combo of how long I have managed to carry him with the administation of steroids means we are most likely to see the results we want today. If we don't, however, I will have to stay pregnant longer. This would be awful for me, for obvious reasons. But if his lungs aren't mature, it means that after delivery, we can guaruntee he will need to be on a ventilator of some sort. I don't want that. No mother does. So if the results aren't favorable, I 'll have to endure whatever comes next, which will most likely be more steroid injections and more waiting. More pain and contractions. But at that point, I will know, without a doubt, that it is necessary, making the thought of it easier to handle.

1 comment:

  1. Wow- thanks for the lesson! I knew about surfectant, but I really did not understand its purpose. I am keeping you guys in my thoughts today.