Saturday, March 1, 2008

March 1, 2008

We have some mixed results today.

Lets start with Ryan. He is still on his CPAP, but they have needed to increase the oxygen concentration (oxygen concentration is expressed as Fixed inspired O2, which is abbreviated FiO2, where the O2 represents elemental oxygen). He was 35% FiO2 last night, and today he is close to 40% FiO2. He tolerated his feedings well, yesterday, and today they will increase the amount of his feedings. Whenever one of the babies is able to increase the food intake, there is a decreased need for the IV nutrition; so more food means less IV support; less IV support translates to a point and time (hopefully) when the IV can be discontinued.

Reese was continued to be weaned from the ventilator last night, and early this morning she was extubated (they removed the breathing tube). She is now on CPAP, just like her brothers, but her FiO2 is almost 50% right now. She tolerated her feedings, yesterday, and is going to have her feedings increased today, as well. Reese's bilirubin level was elevated today, and she has been started on phototherapy (blue light therapy).

Phototherapy uses a blue light shining on the skin. The bilirubin gets to the skin, via the blood supply, and it absorbs a specific wavelength of light; this causes the bilirubin to become partially oxidized, which makes it more water soluble. Once it reaches a point of oxidation that is easily water soluble, it can be eliminated by the kidneys. Usually bilirubin is removed by the liver, but the liver depends upon stool formation in order to be able to dump the bilirubin; babies sometimes take several days to produce stool; this is especially true of premature babies; because they are getting fed slowly, they have not yet produced any stool, so their livers cannot dump the bilirubin. I will attempt to explain this more a little bit later.

Rylie had an apneic episode last night (he quit breathing); this is not uncommon in premature infants, but this was the first problem that he has had. He had to be stimulated by the nurses last night in order to get him breathing again. He has had a few more apneic episodes this morning, but he has not needed any further stimulation in order to start breathing again. Yesterday his FiO2 was 21% (the same as room air), but during the night it was necessary to increase his FiO2 to 35%. His bilirubin level is elevated, so he is now getting phototherapy.

When we went to the NICU this morning, part of it was closed because of an admission, so we only got to see Rylie.

We went back this afternoon, and we got to see all the babies.

Rylie is doing well with his increased feedings, but his FiO2 has been increased again to almost 40%. The nurse said that he has not had any more apneic episodes since this morning.

Reese is tolerating her CPAP and feedings. Her FiO2 is now down to 40%.

Ryan has the amount of his feedings doubled today and seems to be having some trouble with that. Whenever the body digests food, it has to shunt blood away from other body areas and shunt blood to the bowel. This puts an increased burden on the heart and requires increased oxygen demand. Ryan is now close to 50% FiO2. If he gets to 60% FiO2, they may need to intubate him. Part of the problem centers around the CPAP. Because the CPAP constantly blows pressure into the back of the nose and throat, it tends to blow air down into the stomach. This causes stomach distention. Stomach distention pushes up on the diaphragm and that limits how much the lungs can expand. Limited lung expansion means that the lungs are not functioning at their full capacity, but the CPAP helps to offset this by making it easier for the baby to take a breath. So, the CPAP is a mixed blessing.

Because the babies are getting phototherapy, they have special eye coverings. Then the CPAP covers most of the rest of their faces so it is hard to see much of anything today. That, combined with the fact that we forgot to take the camera with us today, means we did not get any pictures today (sorry about that).

Ryan did not have eye coverings because he is scheduled to start phototherapy, but it has not been instituted yet. He opened his eyes for us today. He did not open them enough that we could tell anything about eye color, but he was looking at us and his eye tracked us when we moved (that is a good sign of higher brain function and cranial nerve function).

Okay, lets get into bilirubin and a few other things, shall we. Prepare yourselves; I am never one to give a simple answer (a fact to which Shelley will attest). I want to suggest that you go to www.m-w.com. There you can enter a word, click the box for the Medical Dictionary, and it will give you definitions for most of the terms that you will encounter in this post.

Before babies are born, they produce fetal hemoglobin which, is composed of 2-alpha units and 2-F units (the F stands for Fetal). This is very important because the fetal hemoglobin binds oxygen more tightly than adult hemoglobin does; therefore, the oxygen from the mother's system (adult hemoglobin) will release oxygen at the placenta, and the baby's system (fetal hemoglobin) binds the oxygen, and the oxygen is then transported to the rest of the baby's system. Fetal hemoglobin also releases oxygen better when it gets to a high Carbon Dioxide environment (Carbon dioxide is CO2, and is the waste product of normal cell function). So, when the oxygenated fetal hemoglobin gets to an area that has elevated CO2 levels (at the capillaries), it releases its oxygen to the cells in that area. This is all very important for the baby to be able to get the oxygen that he, or she, needs.

Once the baby is born, and begins to breath, things change considerably. Now the baby is breathing air and getting a higher concentration of oxygen than what was available from the mother's circulation. The fetal hemoglobin continues to bind the oxygen tightly, as it did before birth. However, the CO2 content at the capillary level is less than before the baby was born. The main reason for this is because the CO2 is easily dissolved in the fluid portion of the blood (the hemoglobin does bind CO2 weakly, but it is not a major factor in the transportation of CO2 throughout the body). Because the baby is breathing and blowing off CO2, CO2 levels are diminished throughout the baby's entire system. This means that there is less CO2 levels at the capillaries; and less CO2 means that the fetal hemoglobin does not release the oxygen as well in the area where the cells need it. The cells are not starved for oxygen, but as you can see, fetal hemoglobin is not the best hemoglobin for a breathing baby. Shortly after the baby is born, the baby's system recognizes the change, and stops producing fetal hemoglobin, and starts producing adult hemoglobin (adult hemoglobin has 2-alpha subunits and 2-beta subunits).

As the adult hemoglobin is produced, the fetal hemoglobin starts to break down. When the hemoglobin breaks down, it binds with a protein in the blood stream (Haptoglobin), which transports it to the liver (haptoglobin bound hemoglobin is a short term storage solution). The liver metabolizes the hemoglobin to bilirubin (this is unconjugated bilirubin at this point; conjugated bilirubin will be discussed a short while later) and releases it back into the blood stream. Unconjugated bilirubin is not water soluble, so it is bound up by a different protein that is called Albumin. The albumin bound bilirubin is a medium term storage option; it keeps the bilirubin suspended until such time as the liver gets an opportunity to metabolize it further. The liver will take up the bilirubin and attach a modified glucose molecule to it, at which point it becomes conjugated bilirubin. Conjugated bilirubin is water soluble and can be transported in the blood without needing to be bound to any protein molecules. Once it reaches the kidneys, conjugated bilirubin can be acted upon by a specific enzyme that turns it into Urobilinogin, which is even more water soluble, and this can be secreted by the kidneys. However, this is a minor route of elimination of bilirubin. Most of the conjugated bilirubin gets excreted by the liver into the bile and passed into the duodenum (the very first part of the small bowel). Then the bilirubin passes down througn the small bowel. As the bilirubin passes through the small bowel, the modified glucose molecule gets digested off, and we once again have unconjugated bilirubin. When it gets to the lower end of the small bowel (the area knows as the ileum) the bilirubin gets reabsorbed into the blood stream. Bilirubin has an iron atom at its core, and the reabsorption of the bilirubin represents one of the body's mechanisms to conserve iron, and allow the liver to process it to a slightly different form that can once again be utilized by the body for blood formation (and other uses).

In order for the bilirubin to be eliminated from the body, there has to be enough material moving through the bowel so that the bilirubin gets carried past the small bowel without getting reabsorbed. Since the babies are only getting small feedings, there is not yet a sufficient quantity of material to move the bilirubin through the bowel quickly enough to prevent reabsorption, and so a large quantity of the bilirubin gets reabsorbed into the blood stream. This is the beginning of the problem.

There is a limited amount of albumin, therefore there is limited ability for the unconjugated bilirubin to remain suspended in the blood stream. The liver has a limited ability to conjugate the bilirubin; this is due to a number of reasons. Part of it has to do with the change in blood flow as the baby converts from fetal circulation to adult circulation. Part of this has to do with the fact that, since there is a high demand for new adult hemoglobin (and therefore, new Red Blood Cells [RBC's]), the liver, for a short time after birth, actually spends a good deal of time and energy producing new RBC's (the spleen also acts as an area of new RBC production during this time). As a result, the bilirubin starts being deposited anywhere that it can go. The unconjugated bilirubin is not water soluble, but it is lipid soluble (it can be dissolved in oil and fat). So, the bilirubin starts to collect anywhere there is a high concentration of lipids. This is not a problem for a typical fat cell (adipocyte or adipose tissue), but it is a problem for the brain.

The insulation around the neurons of the nervous system is composed of a highly specialize cells; in the central nervous system, CNS, which is the brain and spinal cord, these cells are oligodendrocytes; in the peripheral nervous system, those cells are Schwann Cells. These cells provide an insulating wrapping that lets the nerves function properly. The wrapping around the nerves is called Myelin, and the major component of myelin is Sphingomyelin. Sphingomyelin is compose of a modified lipid (0il).

Because the unconjugated bilirubin can dissolve in lipids (which are fats and oils), it can dissolve into the brain tissue. This can lead to a problem know as Kernicterus. Kernicterus is best known to occur with erythroblastosis fetalis, which is something that occurs as a result of ABO incompatibility between the mother and the baby; but erythroblastalis fetalis is not the only thing that can cause a high enough bilirubin level that can lead to kernicterus. Thankfully, phototherapy has been available for many years and is a very effective means of making the bilirubin more water soluble, so that it can be more easily eliminated from the baby's system. I will not bore you the details of the biochemistry involved in the photo-oxidation conversion reactions of bilirubin; you can look that up on the internet if you are so inclined.

Okay, the physiology and biochemistry lesson is complete for now.

I can convey many things to you in my words, but I have yet to find a means to be able to communicate just how much I love these little ones. It sometimes makes me cry when I see them and know that they are isolated, and that all I can do is touch them occasionally. Even touching them has to be soft because their skin is so sensitive, that anything more than light touch can be painful. I know that everyone is praying for angels be around them and to hold them and to comfort them, but it still hurts to not be the person that is able to do that.

I will go ahead and post this today so that you will be able to get some new information.

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