As a parent in the NICU I lost count of how many times I got the PDA demonstration. I think most nurses love to demonstrate their medical knowledge and the PDA is something that they all feel they know something about. Out comes the giant picture of the blue and red heart and then comes the spiel. I heard it enough times that I should know it verbatim. Unfortunately every version was different, so without further research I would have been left confused. I often noticed other couples getting the cot-side impromptu presentation nodding along furiously then looking bemusedly at each other when the nurse disappeared.
PDA stands for Patent Ductus Arteriosus. Patent in this sense means "open", not "shiny" as in patent leather shoes. So, the Ductus Arteriosus is open, it should be closed.
What is the Ductus Arteriosus?
Pre-birth we all live in water, amniotic fluid. There's an argument that even after birth we all live in water, only we carry our ocean around with us. The word "amniotic" comes from the Ancient Greek word for bowl. So, as we live our pre-birth goldfish like existence in our bowl of water, how do we breathe? Well, our mothers do our breathing for us. Oxygenated blood is passed through the placenta from the mother to the fetus, thus leaving the fetus' lungs alone to concentrate on developing. That is why they are the last of the organs to develop before birth. This is also why so many premature babies have breathing difficulties and are constantly monitored for oxygen saturation. It is very difficult for the premature baby to maintain suitable oxygen saturation in her own blood using her own undeveloped lungs. To compensate for this, the baby is given an air supply with more concentrated oxygen levels than normal air (which is around 21% oxygen, the rest being mostly nitrogen).
So, what does the DA do? Well, when it is "patent" (ie "open") it allows the blood to flow through the heart without going through the lungs. There's no point pushing the blood through the lungs when they are immature and fluid-filled, they can not yet oxygenate the blood. In a full-term birth, the duct will close itself off anywhere from a few hours after birth to a few weeks. It does this by becoming more fibrous and eventually sealing itself off.
What does this mean for a Premmie?
In most preterm births the PDA will remain. The amount it is open is normally described in millimeters and can be anything from less than half a millimeter open to a few millimeters open. Normally, a PDA is evident to the doctor listening through a stethoscope as a background murmuring like a motorbike. An echo-cardiogram will almost certainly be performed to measure how open the duct is. This is a simple non-invasive test, just like an ultrasound.
After the test, the doctors will determine a course of action to close the DA if required. Well, that's if you're in a NICU which has a philosophy of closing PDAs. Like many matters in the NICU, there will be a philosophy in that Unit which is unique to that unit. Some will try to close the PDA with gusto, others will decide if the PDA is "hematologically significant" and take action based on that. That means, they will decide if the DA being open is a problem or not.
Treatment will either be pharmaceutical or surgical. The surgery is relatively uncomplicated. They will "ligate" the PDA, ie tie it off. Normally they will opt for a pharmaceutical approach to begin with. Commonly, a course of indomethacin is prescribed. The indomethacin is normally given as a course, the frequency and strength of which again will vary from NICU to NICU. Why this would vary is not clear to me. Surely some consensus of medical best practice has been reached and adopted by all clinicians? Not so, unfortunately. This variability is a recurring theme for most most decisions concerning premature babies. All I can suggest is that you research thoroughly, arm yourself with as much knowledge as you can and not be afraid to ask questions in the NICU. There really is no such thing as a stupid question.
In some countries a more successful drug for closing the PDA has been Ibuprofen, which is commonly taken for headaches. This isn't approved for use in all countries yet though, so may or may not be offered depending on your location.
Hopefully, the first course of drugs will close the PDA or at least reduce it to a size that is no longer significant. If not, another course of indomethacin may be prescribed. From memory, it has around a 30% efficacy so two courses will make it more likely than not that the DA will be closed but it is still reasonably possible that it won't be. There's a limit to how many courses of indomethacin will be administered. Two in our case, but again this will depend on the dosage used, which is variable unit to unit. Hopefully by this point the DA will now be significantly smaller. If not, surgery will probably be necessary. This surgery is a lot less invasive than it used to be.
( Scott L Miller )