Premature Babies Should Have Temperature Monitored at 2 Sites
An Expert Interview With Robin Knobel, PhD, RN
Editor's note: Monitoring temperature on the abdomen and the foot of extremely low-birthweight infants can yield important clues about an infant's condition, according to information presented at the National Association of Neonatal Nurses (NANN) 28th Annual Educational Conference in Palm Springs, California.
Robin Knobel, PhD, RN, assistant professor at the Duke University School of Nursing in Durham North Carolina, and a Robert Wood Johnson Foundation nurse faculty scholar, shared her research at the conference. In a telephone interview withMedscape Medical News, she discussed what nurses can learn from this type of monitoring.
Medscape: What prompted you to study temperature regulation in extremely low-birthweight infants?
Dr. Knobel: I worked as a NICU [neonatal intensive care unit] and a neonatal nurse practitioner. We did a lot of transport, and it would always impress me how cold the babies were when we would pick them up. Nurses would take care of everything — blood pressure, ventilation, all those vital things — but many times they would forget about the temperature.
Once I picked up a really cold baby who ended up dying because he was so hypothermic in the beginning. I also saw many hypothermic babies coming from the delivery room who would be cold from the delivery experience. I decided that I wanted to do something to improve temperatures for babies.
Medscape: How do premature infants respond to cold temperatures?
Dr. Knobel: Infants up to about 32 weeks of gestation do not have the ability to warm themselves effectively. All infants up to about 1 year of age use nonshivering thermogenesis. They do not have the ability to shiver, like adults do. The problem with infants up to about 32 weeks is that they are deficient in thermogenin and 5ˊ/3ˊ-monodeiodinase enzymes.
They have brown fat — they actually have enough to keep them warm — but because they are lacking in sufficient amounts of the enzymes, they don't have the ability to effectively produce heat using nonshivering thermogenesis. Similar to reptiles, [infants of that age] will continue to lose heat if not kept in heated incubators. This warm environment will allow nurses to keep babies warm. We regulate the incubator with the incubator servo control (ISC); we set the temperature to where we would like to maintain the baby, and the incubator heats up to keep them at that temperature.
One problem with very premature babies is that there are not good recommendations on keeping the baby warm enough. We need guidance on where to keep the baby's temperature so that when the baby is exposed to cold environmental temperature during care, it does not cause hypothermia.
Most studies have been done on infants who were more mature than 29 weeks. We really need published guidelines on where to keep these more premature babies.
In one of my previous small studies [J Obstet Gynecol Neonatal Nurs. 2010;39:3-14], we found that the babies kept a more normal heart rate when their body temperature was between 36.7 °C and 36.8 °C. Most NICUs set ISC temperatures around 36.5 °C for premature babies. The American Academy of Pediatrics (AAP) defines hypothermia at less than 36.4 °C; trying to control at 36.5 °C is probably a little low because it's bordering on being too cold for those babies.
Medscape: Your research has evolved as you've learned more about this issue. Can you describe your work in this area?
Dr. Knobel: As a neonatal nurse practitioner, I was involved in one of the first studies designed to prevent heat loss in premature babies by putting the babies in plastic bags in the delivery room [J Perinatol. 2005;25:514-518]. The study was successful in improving admission temperatures in the NICU. Because other studies also found that using plastic wrap or bags in the delivery room prevented heat loss, the AAP changed national resuscitation standards in the Neonatal Resuscitation Program to include placing babies in either plastic wrap or plastic bags in the delivery room if they are younger than 29 weeks.
After that, I moved on to look at temperature during the first 12 hours of life, because stabilization is the most critical time for the little ones [J Perinatol. 2009;29:814-821]. They really get cold during all of the procedures and everything that we do to them.
We monitored temperatures every minute for the first 12 hours of life in infants less than 29 weeks' gestational age, and found that babies got really cold, sometimes down to 34 °C. By actually measuring temperatures every minute, we saw hypothermic body temperatures that you do not see when you are a nurse at the bedside, looking at the baby every 4 or 6 hours.
The most impressive thing that came out of the very first study, which was my dissertation study for my PhD at the University of North Carolina, Chapel Hill, was that the foot temperature was staying warmer than the abdominal temperature many times for 8 of the 12 hours in 8 of 10 kids. That is really unusual. A baby should not be warmer peripherally than centrally. I also found that they did not have the ability to constrict the blood vessels in their feet and send blood centrally to warm up their body in response to hypothermic body temperatures.
Medscape: Are you conducting any research right now?
Dr. Knobel: We are looking at body temperature over the first 14 days of life, to see when babies are mature enough to keep their central body warm.
This study, funded by the National Institutes of Health (NIH) and the Robert Wood Johnson Foundation, is examining 30 babies, all younger than 29 weeks' gestation. We have enrolled 26 of 30 babies so far. We've added some measures to try to get a picture of body temperature and perfusion throughout the body. We measure their abdominal and their foot temperature with a skin surface temperature probe, similar to the standard temperature probes used in the NICU.
We do that every minute for 14 days, which gives us about 20,000 data points on each baby. We also measure perfusion index with a Masimo pulse oximeter; it measures blood flow to the foot. If a baby has a warmer temperature in the foot than in the abdomen, we can look to see if there really is good perfusion in that foot, which is causing the foot to be warm. We have not analyzed those data yet.
We are also conducting infrared imaging with a $50,000 infrared camera, purchased by the Jean and George Brumley Jr. Neonatal-Perinatal Research Institute at Duke University [Biol Res Nurs. 2011;13:274-282]. We take images of the baby once a day, every day for 5 days. That gives us an overall look at their body temperature. You look at the temperature as a black and white picture, with the white being the hottest temperatures and the black being the coldest. Every time you move your cursor over the picture on the computer screen, you will get a temperature for each spot, so we can look at areas of temperature to see if the abdomen is really cooler than the foot.
We also record continuous video of the baby in the incubator. We code the video for procedures that are being performed on the baby, and we match it up with temperatures measured at the same time. We are trying to see what we are doing to the baby and how it affects temperature.
This study provides a lot of data. We have analyzed some of the temperatures, but we have not analyzed all of the other data yet. That will take another year.
Medscape: What do you think is causing this to happen?
Dr. Knobel: We are still seeing many periods of the foot temperature being higher than the abdominal temperature, but it does not seem to be due to immaturity. It looks like it is due to instability, because it not only occurs in the first day of life, when the baby is transitioning from the uterus to the neonatal period, it is also occurring in different time periods throughout the 2 weeks. It looks like it is correlated with the infant either getting sick or being sick.
The next big study that we have already written a grant for (and submitted it to the National Institutes of Health) will be to look at the periods when the foot is warmer than the abdomen, and look at that in relation to necrotizing enterocolitis (NEC). I think there is a link between the abdomen being cold and possibly having some ischemia during that time, leading to NEC after feedings are started.
Medscape: What steps should NICU nurses take to preserve the body temperature in these babies?
Dr. Knobel: If they can leave the baby alone, then the heat in the incubator will stay in the incubator; the doors won't be open, allowing the cold air to rush in and make the baby cold.
If we have less stimulation to the baby and allow the baby to maintain body heat, the baby will be more stable.
There has been a lot of literature suggesting that we should monitor 2 temperature areas of the baby's body instead of just 1. My research is confirming this practice. Monitoring an abdominal temperature, which is the standard of care, is good practice, but if you monitor the foot temperature also, you will have a better sense of the baby's thermal status.
Some units do monitor 2 areas, but others do not. This practice would allow nurses to see when the foot is warmer than the abdomen, which is an abnormal perfusion state — the periphery shouldn't be warmer than the core. If nurses can see when the baby is in this abnormal state, then they could opt not to feed the baby or conduct procedures during that time, and would know that the baby is already compromised.
Also, keeping the ISC between 36.7 °C and 36.8 °C would improve body temperature and guard against heat loss in babies less than 29 weeks of gestational age.
Medscape: Do you have any future research planned?
Dr. Knobel: In the future, I'd like to look at the link between central and peripheral temperature differences and morbidity. NEC is still one of the worst morbidities for babies; the mortality incidence is from about 10% to 50% in babies who get NEC. We are seeing preliminary evidence that there is an association between an abnormal perfusion state (when the feet are warmer than the abdomen) and the incidence of NEC. Our next study will be a multisite study, with 3 different NICUs, looking at temperatures over the first month of life and looking at NEC outcomes for the first 2 months of life to see if we can connect the 2.