Thermal Stability of the Premature Infant in NICU
As an infant matures and nears hospital discharge or transfer from the NICU, we must wean the infant from an incubator to an open crib. There has long been debate about the best way to wean an infant from the incubator and the weight to begin the weaning process. There is no clear standard to this process and significant practice variation exits. New et al. (2009) surveyed 78 nurse leaders for common weaning practices amongst 109 NICUs in Australia and New Zealand. They found similar weaning practices related to air control, current weight, thermal challenging, single walled incubators and heated mattresses but differing practices related to clothing. When asked the weight where an infant was weaned from the incubator, 48% stated 1800 g, but the range was 1200 to 1800 g. Researchers found that 26% of the NICUs reported an infant would need to demonstrate stable body temperature at an incubator air temperature of less than 29 °C while the majority (40%) of the NICUs specified 29 °C as the target air temperature for weaning. In the units that used gestational age as a requirement for weaning, the target age was 32 weeks. Strategies to insure readiness to wean from heated incubators included using incubator air control (83%), a thermal challenge prior to transfer (85%), placing the infant in clothes (59%), single walled incubators (10%) and external heat sources such as a heated mattress (28%). Less than 50% of the NICUs had written guidelines for weaning an infant from an incubator.
Three research teams have conducted studies to evaluate the weight at which nurses should wean an infant from incubator care to an open crib. Schneiderman et al. (2009) conducted a retrospective study and found that each 100 g the infant weighed at the time of weaning to an open crib was associated with an increased time of 0.8 days until full feedings by mouth and an increased length of stay by 0.9 days. The researchers found that weaning at a weight greater than 1800 g resulted in increased time to full feeds, increased length of stay and decreased daily weight gain. They recommended 1500 g as the target weight in which to transfer to an open crib.
Italian researchers also found that infants transferred to an open crib at weights less than 1600 g resulted in a significant decrease in length of stay (23.5 vs 33 days, p = .0002) when compared to infants transferred at a weight greater than 1600 g. After transfer to an open crib, infants were placed in an environmental temperature of 24 °C and 40% relative humidity, and dressed in a wool hat, booties, two vests, and a cotton wrap. The nurses checked hourly axillary temperatures until there were two readings ≥ 36.5 °C. If the axillary temperature was found to be lower, then another wrap was added and temperature was rechecked in two hours. If still less than 36.5 °C, the infant was returned to the warmer and the temperature was checked in three hours. If after that the temperature remained low, the infant was returned to the incubator. No infants required transfer back to incubator. These researchers determined weaning to an open crib was safe at 1600 g and resulted in earlier discharge.
New et al. (2012) conducted a multi-center, randomized trial to compare groups weaned at 1600 versus 1800 g with primary outcomes of temperature stability and weight gain at 2 weeks of age. Infants in the 1800 g weight group had more temperatures less than 36.4 °C than the infants had in the 1600 g weight group in the first 72 h. From post transfer to discharge, infants in the 1600 g weight group had more temperatures greater than 37.1 °C. Average daily weight gain for infants in the 1600 g weight group was 17.07 (SD ± 4.5)g/kg/day versus 13.97 (SD ± 4.7)g/kg/day (p = < .001) in the 1800 g weight group These infants were also dressed in a cotton full length jumpsuit, a woolen hat and wrapped in a flannelette sheet and a cotton blanket after transfer to an open crib, with a quilt placed over the infant's clothes. These researchers also recommend transferring infants to an open crib at 1600 g weight. A 2012 Cochrane review also confirms that infants can safely be transferred to an open crib at a weight of 1600 g without adverse effects on body temperature or weight gain.
From current research, we can see that it is deemed safe to wean infants from an incubator to an open crib at 1600 g. Infants have been shown to gain weight better, have more thermal stability and have a decreased length of stay when they are weaned at lower weights than the previous standard of care at 1800 g. More research is needed to define protocols for the process to wean an infant out of the incubator and the standards defining failure to achieve thermal stability once transferred from the incubator.
Weaning From Thermal Care
Practice Variation
As an infant matures and nears hospital discharge or transfer from the NICU, we must wean the infant from an incubator to an open crib. There has long been debate about the best way to wean an infant from the incubator and the weight to begin the weaning process. There is no clear standard to this process and significant practice variation exits. New et al. (2009) surveyed 78 nurse leaders for common weaning practices amongst 109 NICUs in Australia and New Zealand. They found similar weaning practices related to air control, current weight, thermal challenging, single walled incubators and heated mattresses but differing practices related to clothing. When asked the weight where an infant was weaned from the incubator, 48% stated 1800 g, but the range was 1200 to 1800 g. Researchers found that 26% of the NICUs reported an infant would need to demonstrate stable body temperature at an incubator air temperature of less than 29 °C while the majority (40%) of the NICUs specified 29 °C as the target air temperature for weaning. In the units that used gestational age as a requirement for weaning, the target age was 32 weeks. Strategies to insure readiness to wean from heated incubators included using incubator air control (83%), a thermal challenge prior to transfer (85%), placing the infant in clothes (59%), single walled incubators (10%) and external heat sources such as a heated mattress (28%). Less than 50% of the NICUs had written guidelines for weaning an infant from an incubator.
Research Comparing Weights
Three research teams have conducted studies to evaluate the weight at which nurses should wean an infant from incubator care to an open crib. Schneiderman et al. (2009) conducted a retrospective study and found that each 100 g the infant weighed at the time of weaning to an open crib was associated with an increased time of 0.8 days until full feedings by mouth and an increased length of stay by 0.9 days. The researchers found that weaning at a weight greater than 1800 g resulted in increased time to full feeds, increased length of stay and decreased daily weight gain. They recommended 1500 g as the target weight in which to transfer to an open crib.
Italian researchers also found that infants transferred to an open crib at weights less than 1600 g resulted in a significant decrease in length of stay (23.5 vs 33 days, p = .0002) when compared to infants transferred at a weight greater than 1600 g. After transfer to an open crib, infants were placed in an environmental temperature of 24 °C and 40% relative humidity, and dressed in a wool hat, booties, two vests, and a cotton wrap. The nurses checked hourly axillary temperatures until there were two readings ≥ 36.5 °C. If the axillary temperature was found to be lower, then another wrap was added and temperature was rechecked in two hours. If still less than 36.5 °C, the infant was returned to the warmer and the temperature was checked in three hours. If after that the temperature remained low, the infant was returned to the incubator. No infants required transfer back to incubator. These researchers determined weaning to an open crib was safe at 1600 g and resulted in earlier discharge.
New et al. (2012) conducted a multi-center, randomized trial to compare groups weaned at 1600 versus 1800 g with primary outcomes of temperature stability and weight gain at 2 weeks of age. Infants in the 1800 g weight group had more temperatures less than 36.4 °C than the infants had in the 1600 g weight group in the first 72 h. From post transfer to discharge, infants in the 1600 g weight group had more temperatures greater than 37.1 °C. Average daily weight gain for infants in the 1600 g weight group was 17.07 (SD ± 4.5)g/kg/day versus 13.97 (SD ± 4.7)g/kg/day (p = < .001) in the 1800 g weight group These infants were also dressed in a cotton full length jumpsuit, a woolen hat and wrapped in a flannelette sheet and a cotton blanket after transfer to an open crib, with a quilt placed over the infant's clothes. These researchers also recommend transferring infants to an open crib at 1600 g weight. A 2012 Cochrane review also confirms that infants can safely be transferred to an open crib at a weight of 1600 g without adverse effects on body temperature or weight gain.
From current research, we can see that it is deemed safe to wean infants from an incubator to an open crib at 1600 g. Infants have been shown to gain weight better, have more thermal stability and have a decreased length of stay when they are weaned at lower weights than the previous standard of care at 1800 g. More research is needed to define protocols for the process to wean an infant out of the incubator and the standards defining failure to achieve thermal stability once transferred from the incubator.