If you have had a baby born prematurely and are reading this blog post you may have been told that the medical team is looking for a PDA. The PDA stands for Patent Ductus Arteriosus and the last two words Ductus Arteriosus really helped your fetus as it was growing in the womb. In order to understand how it can cause a problem after birth it is first important to understand what it did and why it exists in the first place.
Act I – The Womb
When your baby was developing its lungs the tissue was busy branching into airways that ended in little air sacs called alveoli. Each of those alveoli was next to a capillary which is our smallest blood vessels in the body. One day these units (alveolus and capillary) will happily exchange oxygen that is breathed in for carbon dioxide that needs to be breathed out. In the womb though the lungs were filled with fluid and air was nowhere to be seen. As such, most of the blood (about 90%) that came back from all the veins in the body to the right side of the heart had no business going to the lung. There was just not really any point in sending blood to the lung when it couldn’t pick up any oxygen there. The fetus by having a ductus arteriosus had a “pop off valve”. Since the pressure in the lung was high instead of sending blood to the lung, the 90% went from the right ventricle in the lower part of the heart to the pulmonary artery and from there across the ductus arteriosus to the aorta. The blood following this path therefore basically bypassed the lung and went from the “right” side of the heart to the “left” side that normally sends blood with oxygen to the rest of the body. The oxygen in this case came from the placenta. This fetal ciruculation is shown in the figure below.
Act II – Life on the outside
After birth the lungs fill with air containing oxygen and the resistance to blood flowing into the lung decreases which is a good thing as it allows oxygen to move from the alveolus to the capillary and back to the left side of the heart. As oxygen in the blood stream rises this usually leads to closure of the ductus arteriosus. In preterm babies though the ductus may not shut and this is what we call a Patent Ductus Arteriosus or PDA. This becomes a problem when the blood pressure in the aorta is high and the pressure in the lungs falls with breathing of air. Eventually, instead of the right to left flow of blood that occurred before, you now get blood flowing from the aorta to the pulmonary artery going to the lung and as more and more blood flows to the lungs they start to look white on chest x-rays and it gets harder and harder for your baby to breathe. The mixing is shown below.
Act III -So what do we do about it?
If we suspect that there is a PDA your doctor will order a test called an echocardiogram. This is an ultrasound of the heart and may be done by a specialist in the heart called a Cardiologist or may be done by a Neonatologist trained in doing such tests. Either way if the doctors believe the PDA is causing problems they will suggest a treatment plan to deal with it. The problems that would tend to motivate us to treat would most commonly be that your baby is needed support to help their breathing although problems related to poor blood supply to the kidneys might also lead us to treat.
The mainstays of treatment are two very common drugs and one that you may not have heard of. Indomethacin is a drug that was first used to help close PDAs and is a non steroidal anti-inflammatory (NSAID) drug that is in the same class as ibuprofen (advil) which is another drug that is used. In some centres another very common drug acetaminophen (tylenol) is employed. Most centres at this point are using one of the first two. Regardless after the medicines are given the doctors will order another echocardiogram to see if the PDA has closed and if not may repeat a course of the same medicine or choose a different one.
Act IV – What do you do if it just won’t close?
The next steps depend on how your baby is tolerating the PDA. If your infant is breathing on their own and their kidney function is working well many doctors will just observe and not offer more treatment. Babies though who are on a ventilator or are having significant issues related to their kidneys may rarely need to have a surgeon put a clip on the PDA to close it. These days this is quite rare and there are some centres that choose to not treat the PDA with medicine or surgical closure at all and just wait it out until they are gone. Almost 90% of them will close on their own if you leave them alone but again it depends on how sick your infant is in order to determine if this is reasonable.
If you are reading this and have a baby in the NICU with respiratory distress syndrome (RDS) otherwise known as hyaline membrane disease you might be surprised to know that it is because of the same condition that modern NICUs exist. The newspaper clipping from above sparked a multibillion dollar expansion of research to find a cure for the condition that took the life of President Kennedy’s preterm infant Patrick Bouvier Kennedy. He died of complications of RDS as there was nothing other than oxygen to treat him with. After his death the President committeed dollars to research to find a treatment and from that came surfactant and modern ventilators to support these little ones.
What is surfactant and what is it’s relationship to RDS?
When you take a breath (all of us including you reading this) oxygen travels down your windpipe (trachea) down into your lung and goes left and right down what are called your mainstem bronchi and then travels to the deep parts of the lung eventually finding its way to your tiny air sacs called alveoli (there are millions of them). Each alveolus has a substance in it called surfactant which helps to reduce the surface tension in the sac allowing it to open to receive oxygen and then shrink to get rid of carbon dioxide that the blood stream brings to these sacs to eliminate. Preterm infants don’t have enough surfactant and therefore the tension is high and the sacs are hard to open and easily collapse. Think of surface tension like blowing up those latex balloons as a child. Very hard to get them started but once those little balloons open a little it is much easier! The x-ray above shows you what the lungs of a newborn with RDS look like. They are described as having a “ground glass” appearance which if you recall is the white glass that you write on using a grease pencil when you are using a microscope slide. Remember that?
Before your infant was born you may have received two needles in your buttocks. These needles contain steroid that helps your unborn baby make surfactant so that when they are born they have a better chance of breathing on their own.
Things we can do after birth
Even with steroids the lungs may be “sticky” after birth and difficult to open. The way this will look to you is that when your baby takes a breath since it is so difficult the skin in between the ribs may seem to suck in. That is because the lungs are working so hard to take breath in that the negative pressure is seen on the chest. If your baby is doing that we can start them on something called CPAP which is a machine that uses a mask covering the nose and blows air into the chest. This air is under pressure and helps get oxygen into the lungs and gives them the assist they need to overcome the resistance to opening.
Some babies need more than this though and will need surfactant put into the lungs. The way this is done is typically by one of two ways. One option is to put a plastic tube in between the vocal cords and then squirt in surfactant (we get it from cow’s or pigs) and then typically the tube is withdrawn (you may hear people call it the INSURE technique – INtubate, SURfactant, Extubate). For some babies who still need oxygen after the tube is put in they may need to remain on the ventilator to help them breathe for awhile. The other technique is the LISA (Less Invasive Surfactant Administration). This is a newer way of giving surfactant and typically involves putting a baby on CPAP and then looking at the vocal cords and putting a thin catheter in between them. Surfactant is then squirted into the trachea and the catheter taken out. The difference between the two methods is that in the LISA method your baby is breathing on their own throughout the procedure while receiving CPAP.
Even if no surfactant is given the good news is that while RDS typically worsens over the first 2-3 days, by day 3-4 your baby will start to make their own surfactant. When that happens they will start to feel better and breathe easier. Come to think of it you will too.
Things are tough out there. If you are pregnant you no doubt have lots of questions about living and ultimately giving birth during this difficult time. These guidelines are from Alberta and like with everything these days are subject to change. As of March 23, 2020 this is what is being recommended if you live in Alberta. There are many good things here that are universal no matter where you live. Social distance, wash your hands, avoid touching your face and stay at home if possible.
Once upon a time we would use our gut instinct to inform our decisions as to whether it was reasonable to try and extubate (take out a breathing tube) or to lower or stop CPAP (continuous positive airway pressure). We used to look at home much oxygen a baby needed and what the pressures were on the machine offering them support and combined with what we saw on the patient monitor for oxygen saturation make a decision as to what to do next.
In the last decade or so people realized (as did one of our own respiratory therapists) that buried within all of this data on the patient monitor one could get a report on what percentage of time each infant has spent at different levels of systemic oxygen saturation. A sample report might look like this.
>95% – 10%
90 – 94% – 55%
85-89% – 20%
80 – 84% – 10%
<80% – 5%
Seeing this report though is only half the story. Without knowing how much oxygen on average an infant has received in the last twenty four hours to achieve this range it is somewhat meaningless. The amount of oxygen given may show that we the baby is doing better or worse. For example, if the above histogram was achieved using a range of 25-35% oxygen and was no different than the day before but the infant had been on 30-40% oxygen and pressure the day earlier then we have gotten somewhere! This infant has actually improved. The histogram is unchanged but we have given less oxygen on the same amount of pressure. If the histogram was unchanged but the amount of oxygen was 21-25% the day before, the lungs have gotten worse assuming the same pressure.
It is also worth noting that higher numbers are not alway indicative of a good thing. Take for example this histogram:
>95% – 50%
90-94% – 35%
85-89% – 8%
80-84% – 7%
<80% – 0%
If this infant was on room air and having these numbers I would be overjoyed. What if this was a baby though who was on 30-40% oxygen? These numbers are too good! We know that too much oxygen can be bad for the lungs and eyes. For babies on oxygen we typically target 88-92 % oxygen saturation (others use 90-94%). If we have 50% of the time above 95% oxygen we clearly are using too much and have to cut it back.
As parents you will hear us talk about histograms on rounds and use the information to make decisions about oxygen and the amount of breathing support your baby needs. If you have wondered how we use this information and what this seemingly random assortment of numbers really means, this is how we interpret it. The next time someone says that your infant needs more or less support ask for the histogram information if your unit uses it and you will see whether the data support the change.
It’s not your fault. You come to the bedside often and there isn’t a lot to do while your infant is asleep. There are only so many games, news and social media posts to keep your attention and let’s face it the monitor attached to your infant is a big distraction.
Typically, babies will have their blood oxygen saturation monitored along with their heart rate and respiratory rate. Some babies will have other physiological parameters monitored such as the amount of exhaled carbon dioxide or the blood flowing through their brain (near infrared spectroscopy) but the first three are the most common.
What you need to understand about these monitors is that we set alarms for when we need to know if there is a problem. What you also need to understand is that these alarms while necessary so we know when a baby is in trouble, can also drive you crazy. Parents may become slaves to the monitor where they spend a great deal of the day staring at ever changing numbers. If your infant is a “swinger” meaning that for example their heart rate or oxygen saturation tends to fluctuate a lot this can mean a lot of noise all day long.
One of the things that influences the result on the monitor is something called the averaging time. Typically for us this is 8 seconds which means that the number at any given time being shown is not the number for that second but represents the average number over the last 8 seconds. Sometimes your infant will be referred for a special test called a sleep study to closely monitor their apneic events. Sometimes families are shocked when their infant who seemed to have one or two events a day suddenly is reported as having 30. That is likely because the sophisticated lab is using a 2 or 4 second averaging time. Your baby in this case hasn’t changed. The monitor has. Some of the things that can be asked of the team when you have a baby with frequent events are trying to rule out causes of these alarms that are not due to your child themselves. Is the nasogastric tube in the right place? Should it be changed if your infant’s problem is mostly low heart rate? Could it be that the probe being used to measure oxygen saturation is in need of being changed to a different limb or altogether a new probe used? Typically low heart rate limits are set to 100 BPM. Strictly speaking many would consider this bradycardia but another definition is having a heart rate that is >20% below a baby’s baseline. Some babies are born with a heart rate that is anywhere from 100-110 (normal is usually 120-160). Twenty percent below that could be 80 beats per minute. Should the alarm be lowered to that number from 100? If so many of these alarms will vanish.
Stop Thinking About The Day To Day
Lastly, I would encourage you to try and look at your baby’s progress every few days. The journey through the NICU has many ups and downs. It really is no different than a figure showing the stock market over the last many years. Individual days have their ups and downs but it is the trend over many days that matters. Try not to let the daily events ruin your day. Take a moment and ask your nurse to see how your baby is today compared to a few days or a week earlier. You might be reminded that a week earlier your baby was on CPAP and now is on room air. Overall if they are better try and let that balance out your thoughts and try to not stare at the monitor. It just might drive you crazy.
If there is one question that is asked more than any other it is this one. As I have told countless parents, few really expect to have a stay in the NICU so when it happens you are caught off guard. The normal period of bonding after birth is disrupted and as many families will say, they just can’t wait to go home. When a baby is born preterm though they have to get through many obstacles such as dealing with respiratory distress syndrome, need for CPAP and perhaps problems related to the pesky patent ductus arteriosus. For sure these apply to the babies who are quite preterm but even those who are born later such as between 32-36 weeks or others who are born at term but quite small (we call those intrauterine growth restricted or IUGR infants) have a few milestones to achieve before they can go home. Knowing these are needed may help you on your journey and are summarized here. Please note this applies to my practice and although I suspect will be close to others, there may be some differences depending on where you are.
The “Big Four”
Feedings by mouth
We sometimes confuse families I think when we say on rounds that their infant is on full feeds. What we mean by this is that there is no longer a requirement for any intravenous fluid supplementation. In order to go home though in almost all cases your infant will need to be free of a plastic tube that is either passing from the nose or mouth to the stomach (NG or OG tubes). There are some instances where families may be trained to provide these “gavage” feeds at home but this is the exception rather than the rule. To enable full oral feeding there may be some different nipple and bottle options tried as well as strategies for different frequency of feeding. Typically, babies will be given feeds every 2 or 3 hours (q2 or 3H) and then with time given more flexibility (semi-demand or cue based feeds). When you hear “ad lib demand feeding” that means that they can feed as much as they want and as often as they want to and that means home is close.
When a baby leaves the NICU they will need to travel in a car seat for safety. In order to properly fit in a car seat you need to be about 4 lbs or 1800g. For this reason most centers keep infants until they are about this size. If you have a baby born at 1200g and they need to gain 600g they usually will lose weight for a few days and regain to birth weight by a week or two. Average weight gain for preterm infants is about 15-20g/kg/day which means that after the first couple weeks it would take on average about 30 days to reach the 1800g mark.
Small babies don’t have a lot of fat to keep them warm. As such your small infant starts off life in an isolette or what others call an incubator. Infants are all different but you can expect to begin seeing babies trialed out of isolettes as small as about 1500g. There are many babies who can’t successfully get out into an open crib even up to 4-5 lbs. Don’t be frustrated by this. It will happen but until they can maintain their body temperature outside of an isolette between about 36.3 – 37.4 degrees they will not be able to go home.
As discussed in another post, irregular breathing from apnea of prematurity can last for some time. Units across the globe vary in their approach to dealing with such “events”. On the short end there are units that like to see three days without an event at rest before stopping monitors while others use a five day period and others even longer at 7 or 8 days apnea free. These dips in oxygen saturation and/or heart rate can be VERY frustrating to families. Events that occur with feedings are less worrisome but still usually require a day or two of monitoring before your doctor will let you go. Sometimes they can last for weeks even when feeding seems to have gotten on track. The good news is that they will end eventually.
Of course there are other specific reasons why infants will need to remain in hospital but if you keep track of these “big four” it will give you a rough idea of when home might be around the corner.