PDA (Patent Ductus Arteriosus) - A Parents' Guide For Premature Babies

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 ) 

General Information About Congenital Anomalies

Congenital anomaly is a mental or physical abnormality that is present at, and usually before, birth. Some anomalies may be medically insignificant and may not appear for some time. In other cases, the anomaly may pose a direct threat to life and requires immediate attention. There are, however, some anomalies that cannot be treated.

Question: What are examples of congenital anomalies?

Congenital anomalies include bone disorders, cataract, cleft palate, cretinism, Down's syndrome, congenital heart disease, hemophilia, joint disorders, pyloric stenosis, and spina bifida. Blindness, deafness, hydrocephalus, and jaundice are also often due to congenital anomalies, although in other cases they are the result of event that occurred after birth.

Limbs or organs may be malformed, duplicated, or entirely absent. Organs may fail to move to the correct place, as in cryptorchidism; fail to open correctly as in imperforate anus; or fail to close at the correct time, as in patent ductus arteriosus. Congenital anomalies often occur together. For example, 33 percent of babies born with Down's syndrome also have heart disease.

Question: What may cause the development of congenital anomalies?

They arise from the faulty development of a fetus, caused either by genetic disorders or other factors. Some anomalies arise from a combination of factors, and the underlying cause is far from clear in all cases.

Question: How are genetic disorders responsible for congenital anomalies?

Inherited congenital anomalies generally result from the presence of abnormal genes or chromosomes. Heredity is determined by corresponding pairs of genes, called alleles. One of these paired genes is dominant and the other recessive, and it is the dominant gene that governs the transmitted trait or characteristic. Thus, if the abnormal gene of a pair is dominant, the abnormal or anomalous trait will be conveyed to the embryo. If the abnormal gene is recessive, then both genes in the pair have to be abnormal for a congenital anomaly to occur.

Some congenital anomalies, such as hemophilia, are linked to a defect of one of the sex chromosomes. Many genetic disorders, however, are neither wholly dominant, recessive, nor sex-linked, but may be caused by more than one abnormal pair of genes.

Question: What other factors may cause congenital anomalies?

Infection in the mother is a common cause of abnormality in a baby. For example, an attack of rubella during the first three months of pregnanacy may cause her child to be born deaf or have cataracts, heart disease, jaundice, or other anomalies. Cytomegalovirus (CMV) and toxoplasmosis also cause congenital anomalies.

Certain drugs taken by a woman during pregnancy are often responsible for abnormalities in the child. For example, large doses of corticosteroids can cause a variety of congenital defects, as can some anticonvulsants given to control epilepsy. Other drugs include anticancer drugs; narcotics and sedatives; tranquilizers and antidepressants; antibacterials, especially tetracycline; anticoagulants; drugs prescribed to treat cardiac conditions and hypertension; oral hypoglycemic used to treat diabetes in the mother; and, of course, heavy consumption of alcohol. Other drugs may cause gross abnormalities, such as the defects arising from thalidomide. A pregnant woman should, thus, avoid taking any medication without first consulting with her physician.

Injury to a pregnant woman or to a fetus is another cause of congenital anomalies. For example, limbs may be malformed if an intrauterine device (IUD) is not removed early in the pregnancy. Smoking during pregnancy is implicated as one factor in the incidence of abnormally low birth weight in babies, and malnutrition seems to be related to a high incidence of congenital anomalies. The age of the woman at the time she conceives can also be a factor. For example, Down's syndrome occurs more frequently when conception occurs after the age of about 35.

Congenital anomalies have also been attributed to the effects of X-ray examination made early in a pregnancy.

Question: Is it possible to diagnose congenital anomalies in a fetus?

Yes. The most reliable method of diagnosis is to examine a sample of fluid from the amniotic sac, sometime between the fifteenth and eighteenth week of pregnancy. The sample is obtained by amniocentesis. Microscopic examination of the cells in the fluid then reveals possible abnormalities in the chromosomes. Congenital anomalies that can be diagnosed in this way include Down's syndrome, spina bifida, and anencephaly. Sometimes, the diagnostic use of ultrasound can detect abnormalities of the skull or spine.

Question: Can congenital anomalies be treated?

Treatment depends entirely on the nature and severity of the condition. Many anomalies can be treated, but for some there is no treatment.

Question: In what circumstances might abortion be considered?

Abortion might be considered if serious fetal disorders are found early in a pregnancy. The decision to abort rests with the parents and is made after considering the advice of the physician and specialists on the nature of the disorder and the consequences of abortion.

Question: Are congenital anomalies more likely to occur in first-born babies?

No. Statistics disprove this commonly held belief.

Question: Does a congenital anomaly in a baby indicate that subsequent babies will be similarly affected?

Genetic counseling deals with such questions. In many cases it is possible to state risks numerically. For example, a baby with congenital heart disease is likely to be followed by a similarly affected child in 2 percent of pregnancies instead of the ordinary risk of one percent. Spina bifida occurs in about 1 child in every 1,500, but if a previous child was born with the condition, there is about a 1-in-20 to 1-in-50 chance that it will occur in a later child.

( Amaury Hdz Aguila )