Episode Transcript
Hi and Welcome to Clerkship Ready - Pediatrics - A podcast aimed at helping you excel during your clinical clerkship in Pediatrics.
I am Dr. Joanna Parga-Belinkie, and I am an assistant professor of pediatrics, clinical neonatologist at the Children’s Hospital of Philadelphia, and Director of the well-baby nursery at the Hospital of the University of Pennsylvania.
Today, we will be reviewing what you need to know before your first day caring for newborns in the well-baby nursery or NICU – about the screening and management for neonatal hypoglycemia.
Let’s start with what hypoglycemia is. It refers to having low glucose levels in your blood. How low? That’s a great question, we aren’t completely sure because this is a hard thing to study. What we do know is that prolonged low blood glucose levels can cause something called hypoglycemic encephalopathy. But how low glucose gets, and for how long we can’t really say. No one can test for that in humans when you already know it’s a bad thing for the brain. But we think levels < 40 milligrams per deciliter qualify as hypoglycemia or too low in a newborn baby in their first day of life. And then those levels should rise every subsequent day with levels of less than 60 miligrams per decilitier fitting the definition for hypoglycemia on day of life two to three.
Why do we care if babies have low blood glucose levels? Because glucose is the main fuel for the human body and the brain. And it’s worth saying again – sustained low levels of glucose are bad for the baby’s brain. Even for adults, hypoglycemia can be uncomfortable and they will describe feeling nervous, sweating, being confused or irritable, having a fast hearbeat or being shaky. Babies can’t tell us any of those things. Luckily for the adults listening to this podcast, you can get glucose in three different ways: eating it, breaking down fats or muscle, or breaking down stores of glycogen in your liver. Infants not only can’t communicate their symptoms, they also don’t have the same amount of fat, muscle, or stores of glycogen to help them make glucose to fuel their body – so they rely on eating it. That’s why in pediatrics we recommend, at a minimum, that infants eat every two to four hours – we want them to keep up their energy or glucose levels.
Why might a baby drop their glucose levels when they are first born? Well, we talked about how they don’t have stores of glucose to draw on – but there’s a little more physiology at play. When a baby is in-utero you can think of the placenta being a constant glucose source for the baby that sends sugar right into their bloodstream, a constant glucose infusion for baby. So, baby is born, the cord gets cut, and the glucose infusion is cut off. The baby’s body has to quickly figure out how to calibrate its hormones and the main hormone that regulates the body’s glucose level is insulin. When babies are first born their secretion of insulin is not tightly linked to serum glucose levels. It’s believed that inappropriate secretion of insulin can lead to instances of hypoglycemia in neonates – when their glucose levels are low they can’t turn their insulin secretion down, making their glucose levels drop even lower. Plus, delivery is a physically stressful time for both the mom and baby, and stress can precipitate hyperinsulinism too. A double whammy for baby.
So while every baby might be at some risk for having lower glucose levels at delivery, we don’t check every baby… only the babies who are showing potential symptoms of hypoglycemia or are at highest risk for low glucose levels. What are the signs and symptoms of hypoglycemia? Since babies cannot tell us how they feel, it can be hard to tell. Infants who are “jittery” tend to get blood glucose levels checked. A jittery infant is one who has shaking or tremulous movements of their extremities when they are unwrapped, startled and sometimes even at rest. However, infants are not fully myelinated – meaning that their nervous systems are immature and their central and peripheral nervous systems are not yet connected like they are in adults. So the jitteriness that infants have can be just a sign of immature neuronal connections and is subjective to the examiner – as so many infant symptoms are. Infants with hypoglycemia might also be hard to feed with poor muscle and neurological tone, have breathing problems such as tachypnea or breathing fast or increased work of breathing, be sleepier than normal or lethargic and could even have seizures given the effects on the brain. Infants this sick will generally have other testing too, like looking for sepsis that may land them in the Neonatal ICU. In terms of the babies at most risk for having a clinically significant drop in their glucose levels, those include: babies who are small for gestational age or less than 10th percentile on a growth curve adjusted for their weeks of gestation, large for gestational age or greater than 90th percentile on that same growth curve, premature or less than 37 weeks gestational age, post-term or greater than 42 weeks gestational age, infants of diabetic mothers exposed to higher glucose levels or more swings of glucose levels in-utero, those who have low APGAR scores at delivery, infants with hypothermia, sepsis, or syndromes that might make their glucose levels low, like Beckwith-Widemann syndrome. Additionally, if a mother is on certain medications such as beta blockers or terbutaline – these medications can lower blood glucose levels in the infant. So most nurseries will screen infants with these risk factors. Remember to ask who in your unit gets screened and why, and what level they use to define hypoglycemia – 40 mg/dL is a ballpark but some units might use higher or lower numbers depending on their experiences or protocols. Most nurseries and Neonatal ICUs will have a defined protocol that nurses and doctors follow that gives an algorithm with next steps depending on the glucose, so again ask your resident or attending to have a copy of this.
Babies who show signs and symptoms that might be due to hypoglycemia, or are at risk for hypoglycemia will have their glucose levels checked shortly after birth and then have levels checked or monitored several times during their stay in the nursery. Most nurseries will check glucose levels right before or a feed or aptly named pre-feed glucose levels. We think of hypoglycemia in the newborn as being transient, meaning it should only affect baby for a short period of time, as their body transitions from support in-utero to taking care of itself. Most infants who have transient hypoglycemia after birth will only have it for 48 to 72 hours. It’s good to reassure families that this is a temporary thing that they don’t need to monitor after they leave the hospital.
But what happens to a baby who has hypoglycemia – how do you treat it and do these infants need a Neonatal ICU? Is it safe to keep them in the nursery? Depends – if their levels are really low – we are talking twenties or teens – you might want to consider something like a NICU admission for IV dextrose administration. Very few nurseries would feel comfortable giving fluid and maintaining an IV outside of a NICU. But let’s say you get a border line value of 35 – there are ways to treat hypoglycemia that don’t require an IV. The first is to consider how you are feeding the baby. Is the baby breastfed? There isn’t much breastmilk a mother generally produces early in an infant’s life – a full milk supply can take three to five days to come in. Drops of colostrum while protein rich and excellent nutrition, aren’t exactly a bolus of glucose. If a baby is at risk of having low sugars and has them on testing – you might recommend supplemental milk in the form of donor human milk or formula in the short term to help keep baby’s glucose levels up. Some mothers might even consider early pumping to use their own milk to supplement the baby.
If feeding the baby doesn’t give them enough of a glucose boost – in part because newborn babies have small stomachs so might not be able to take higher volumes of milk – you can also use something called dextrose gel. Dextrose you can think of as a form of immediate energy – it’s what glucose is called when it’s not in the bloodstream but is in the food we eat. Just for fun do you know what lactose – the other common sugar babies eat from milk – breaks down into? If in your head you said glucose you are half right! It’s glucose and galactose.
Now back to dextrose. Dextrose gel is an oral medication that is around 40% dextrose – sweet right? Instead of trying to get the baby to eat it, you can rub it into their buccal mucosa or their inner cheeks to give them a hit of sugar right into their blood stream. It’s not as long lasting or effective as an IV dextrose infusion, but in the short term it can do the trick. Even with dextrose gel consistent feeding should be counseled on and followed to ensure that infants get over the hump of their transient hypoglycemia..
That said, even with consistent feeds and dextrose gel administration some infants are going to need IV dextrose. This can be given as a bolus when the sugars are very low – so again in the teens or twenties. I’ve even had rare cases in which the glucose was so low that the glucometer that we use for testing can’t pick up the value. The bolus dose we give is weight based: 2ml/kg of 10% dextrose solution. Again, we will only write for a bolus if the glucose is very low. If the baby did require a dextrose bolus, or they have borderline sugars that are just under the target needed to protect the brain we place them on a continuous dextrose infusion. Again, dosing this is weight based. Typically we use 10% dextrose and run the fluids at 60-80 ml/kg/day. So if a baby weighs 3 kg the volume of fluid they would need in a day is 180 – 240ml, divided by 24 hours in a day that’s a drip running at 7.5 to 10 ml/hr. You can’t escape talking to a neonatologist without doing some math.
So how much glucose do you give with these drips? .As you can see, in the NICU we love our calculations, and often we will calculate something called a glucose infusion rate or GIR. A short cut for this is to take the concentration of glucose or dextrose in the fluid (10%) multiply that by the rate you are running it (let’s say 10 ml/hr) and divide by 6 times the weight (3kg). For this infant that would give you a GIR of roughly 5.6. A typical starting GIR is around 5 mg/kg/min and you can escalate the infusion rate based on the glucose levels checked in the baby. If the GIR starts to get above 10, it’s getting really high. Also when we give fluids, we try to let babies continue to eat, so you can assume more glucose is getting in their blood from the milk they are drinking. Infants with high or escalating GIR values should be seen by a pediatric endocrinologist as they might have congenital and not transient hyperinsulinemia requiring more work up and checking of hormones like insulin. Additionally, if their hypoglycemia lasts more than 72 hours that might be another indication that an endocrinology colleague should check in. To get off the GIR you usually will wean it slowly. It’s helpful when a NICU has protocols about weaning fluids, but generally you need to stabilize the glucose levels in a normal range for a few checks, then slowly chip away at the GIR by 1 or 2 until you can turn the fluids off. After that, no further checks are needed usually and the infant can be discharged either back to the nursery to room in with their parent or home with family if the birth parent has already been discharged. As a medical student in a busy nursery or NICU, being able to sit with a family and describe why we worry about hypoglycemia - because of glucose being used as a fuel for the brain – can help families understand the treatment their infant needs. Additionally, providing the family with reassurance that this is generally a temporary condition that needs no follow up can be helpful in giving families the information they need to get through their own anxieties about their baby’s health.
So next time you see someone checking a blood glucose level on a newborn baby – ask them why. Is that baby a late preterm infant? Small or large for gestational age? Is it the infant of a diabetic mother? You already know a little of their pathophysiology, and now you should know a little bit more about how to treat it. So you can learn from the cases you see and the families you have the privilege of caring for.
Thanks for listening to Clerkship Ready - Pediatrics. I hope you found today’s podcast helpful. Don’t forget to subscribe below and rate the podcast!
