If you have an infant in the NICU and they were born at less than 2500g you probably have noticed that we tend to feed these babies very slowly. As you descend into the very early gestational ages and see babies under 750g or 1250g we feed these babies even more slowly. You may have heard your nurse or doctor talk about MEF or minimal enteral feedings. Typically these feeds are about 1 ml/kg of body weight given every couple of hours. If you have a 1kg baby then that would be about 1 mL of milk every couple hours. This is done for about 3-5 days and really “feeding” is a bit of a misnomer as what you are really doing is trying to “prime the pump”. By exposing the newborn gut to small amounts of breastmilk this MEF is really designed to help the bowel adapt to what is coming which is larger volumes of milk. We prefer that this milk is from humans as opposed to cow’s as the bowel tolerates this type of nutrition far better.
Once we start increasing feedings it may seem like it takes forever to get to what we call full feeds. We tend to increase the amount of oral feedings by anywhere from 20 – 30 mL/kg/day until we reach somewhere between 150-165 mL/kg/day of milk intake. During this time you may hear about us using TPN which stands for total parenteral nutrition. This is a combination of fats, sugars and protein plus important vitamins and minerals that we have in a liquid form (yellow and creamy white) that we give your baby so they get what they need while awaiting their feeds to reach the full point. While it may seem like a long time, it is not by accident. What we are trying to avoid is a condition called necrotizing enterocolitis (NEC). NEC is typically diagnosed on an x-ray but more recently people are using ultrasound to identify it. It can present clinically in a variety of ways but the one that usually triggers us to think about NEC as a possibility is blood in the diaper. This may be related to an intolerance to cow’s milk protein but if it is NEC we may also see other signs such as a distended belly, pain when we push on it or changes in vital signs such as temperature fluctuations and fast heart rates. Some babies may also present with failure to breathe and have pauses that may initially be thought to be just apnea of prematurity. NEC fortunately is less common than many years ago but it still occurs with varying frequency in babies under 33 weeks for the most part. The Canadian Neonatal Network is a group of 32 NICUs in Canada and tracks a number of conditions with NEC being one. Here is how the different sites compare across the country. What you can see from the graph is that the incidence varies but is generally abut 4-5% or about 1 in 20 babies in the NICU under 33 weeks.
The simplest way to think of it is that the lining of the bowel on its innermost surface absorbs nutrition but also has a dual role of keeping bacteria in the gut space and not allowing any to get into the tissues of the bowel. If the lining breaks down and allows bacteria to get into the tissues then we have the start of NEC. If this progresses we can ultimately see gas being produced in the bowel wall on x-ray and sometimes this gas escapes into the circulation of the liver and you will hear someone talk about “portal venous gas”.
NEC is a serious condition that if caught early may heal up but even in those cases on occasion the tissue damage can be permanent and lead to dead (necrotic) bowel being removed. When this happens the healthy bowel is typically brought up to the surface of the skin and a plastic pouch applied to the skin to catch the intestinal contents. This allows for the portion of bowel in the belly to heal and at some point many weeks later the bowel will be reconnected.
What can we do to prevent NEC?
- slow advancement of feeds
- exclusive human milk diet
- probiotics may be beneficial