22.4: Neutral Thermal Environment
By the end of this section, you will be able to:
- Illustrate the importance of maintaining a neutral thermal environment when caring for a newborn patient
- Compare and contrast all four ways that a newborn can lose heat and verbalize ways a nurse can help maintain a neutral thermal environment
- Discuss the importance of the Ten Step Warm Chain and how it impacts the care given to a neonate
- Summarize the signs and symptoms of cold stress and how to care for a newborn with cold stress
One of the most vital goals for a nurse caring for a neonate is providing support to maintain their temperature while they transition from intrauterine to extrauterine life.
Thermoregulation in the Newborn
The thermal balance created by the loss of heat to the environment at a rate equal to the heat being produced is called thermoregulation . Neonates have a poor ability to maintain thermoregulation because they have very little brown adipose tissue that stores the energy useful for creating heat. The neonate is also unable to shiver, which is a reflex helpful in raising temperatures. Maintaining a thermoneutral environment, between 36.5° C (97.7° F) and 37° C (98.6° F), throughout the transitional period is essential for a neonate. An appropriate temperature environment can be maintained via radiant warmer , swaddling (Figure 22.8), and skin-to-skin contact with the birthing person, the partner, or available extended family (Fraser, 2014).
Heat Loss in the Newborn
Neonates can experience heat loss in the hospital or home environment in four ways: radiation, evaporation, convection, and conduction. Neonates are homeothermic , meaning that they attempt to stabilize their core internal temperature despite significant temperature variations in their environment (Fraser, 2014; Trevisanuto & Sedin, 2016). A neutral thermal environment is the minimum temperature range necessary for heat production to maintain normal body temperature (Fraser, 2014; Trevisanuto & Sedin, 2016) (Figure 22.9). Term and postterm neonates require higher environmental temperatures than adults to maintain a neutral thermal environment, between 20° C and 22° C (68° F and 72° F).
Several neonatal characteristics affect thermal stability:
- Heat transfer from the newborn’s organs to skin surface is increased compared to that of adults because of the neonate’s decreased subcutaneous fat and large body surface–to–weight ratio (Fraser, 2014; Trevisanuto & Sedin, 2016).
- The blood vessels in the neonate are closer to the skin than those of an adult. This causes the circulating blood to be more readily influenced by environmental temperatures, thus influencing the hypothalamic temperature-regulating center in the brain (Trevisanuto & Sedin, 2016).
- Newborns rely on nonshivering thermogenesis for heat production via metabolism of brown adipose tissue (Fraser, 2014).
- At birth, the newborn prefers to stay in a fixed posture, decreasing the surface area exposed to the environment, reducing heat loss (Trevisanuto & Sedin, 2016).
Evaporation
One of the most common ways that a neonate experiences heat loss in the birthing room and on the postpartum unit is evaporation , which is heat loss that occurs when liquid is converted to vapor. The amniotic fluid and/or blood on the infant holds water that cools the neonate when exposed to the cooler environment (Figure 22.10). Evaporation can also occur if the neonate is tachypneic and exhaled moisture or water is escaping from the respiratory tract. Radiant warming beds and phototherapy can also cause evaporation heat loss (Fraser, 2014; Interprofessional Education and Research Committee of the Champlain Maternal Newborn Regional Program, 2013). Neonates are at particular risk of heat loss via evaporation at the time of birth and during their newborn bath. In the birthing room, the nurse can use warmed blankets to dry the neonate, discarding wet ones and replacing them with dry ones as needed. At the newborn bath, the nurse exposes only the necessary areas of the neonate and ensures that they have had stable temperatures before bathing.
Convection
The loss of heat from the body surface to the surrounding air by a current, like a fan in a room, is called convection . This can be caused by a fan, an air-conditioned room, removing a neonate from an incubator for a procedure or feeding, or even unwarmed oxygen in a mask. The impact on the neonate depends on the amount of time they are exposed to the cooled air, the velocity of the moving air, the temperature difference between the neonate’s skin and the air, and the amount of body surface exposed. (Lubkowska et al., 2019).
Conduction
The loss of heat when in direct contact with a cooler surface is called conduction . Nurses caring for a newborn can prevent this loss of heat by warming their hands, using warm blankets on scales and examination tables before placing the newborn on them, warming stethoscopes, and prewarming the warmer or incubator (Isolette) prior to placing the infant on the bed. Placing a neonate skin-to-skin with the birthing person, their other parent, or an extended family member is a very effective way to warm the neonate and prevent conductive heat loss.
Radiant Heat Loss
Another way that a neonate experiences heat loss is through radiation , which is heat loss occurring from transfer of heat to cool solid objects not in direct contact with the newborn. The walls or windows in a room, for example, can transfer heat from the neonate’s body if the crib or incubator is placed too close to a cold space (Fraser, 2014; Interprofessional Education & Research Committee, 2013). If a nurse places a bag of ice near the newborn in the crib or incubator while preparing to draw blood gases, that will increase radiant heat losses. Placing a hat on the newborn conserves heat, decreasing radiant heat loss. The nurse and parents must be very aware of where the newborn is placed because radiant heat loss for a newborn can happen quickly.
Figure 22.11 summarizes the methods of heat loss.
South African Cultural Attitudes about Neonatal Baths
In the Vhembe District, Limpopo province of South Africa, indigenous people do not bathe newborns only for hygienic purposes. They mix indigenous herbs with the bath water for protection from evil spirits carried by people, as well as general well-being and relaxation. The traditional bath that occurs in the first three to four days of life, gumululo , contains three traditional medicines that are boiled with water and added to the bath in place of soap. The bath is given to neonates to make them strong and protect them. At the end of the bath, they offer a small amount of the bath water to the neonate to drink (Tuelo & Mulaudzi, 2021).
Ten-Step Warm Chain
The ten-step warm chain was developed in 1997 by the World Health Organization in advocating for a more standardized approach to support thermal stability in the newborn (World Health Organization, 1997). While not the standard of care in the United States, the ten-step model is still widely used in low-resource countries. The ten steps include
- warm delivery room,
- immediate drying,
- skin-to-skin contact,
- breast-feeding,
- bathing and weighing postponed,
- appropriate clothing and bedding,
- mother and baby together,
- warm transportation,
- warm resuscitation , and
- training/awareness-raising (World Health Organization, 1997).
According to the ten-step warm chain, the delivery room should be at least 25° C (77° F) with no drafts, with no fans moving air around, and with all supplies needed to keep the newborn warm prepared ahead of time (World Health Organization, 1997). At no time should the birthing person, visitors, or nurses change the temperature of the delivery room. Immediately after the birth, the nurse can prevent heat loss in the neonate by drying the newborn with a warm blanket or cloth to prevent evaporation (World Health Organization, 1997) After drying the infant, the nurse will place the newborn on a warm surface, such as skin-to-skin with the birthing person’s chest or abdomen or in the radiant warmer to prevent conductive heat losses. This is when the nurse should encourage the birthing parent to initiate breast-feeding, according to the ten-step warm chain (World Health Organization, 1997). Bathing must wait until at least 6 hours post birth or by 24 hours of age and when the newborn’s temperature has been consistently stable (Association of Women’s Health, Obstetric and Neonatal Nurses [AWHONN], 2019; World Health Organization, 1997). Bathing should be done quickly with warm water. The newborn should be dried thoroughly, dressed in appropriate clothing, and given to the birthing person to be kept warm. If transportation is necessary, skin-to-skin with the birthing person is safest and recommended. If that is not possible, the next best option is a fully clothed newborn, swaddled, and in the arms of another adult or a transport device (World Health Organization, 1997).
Cold Stress in the Newborn
When a neonate loses more heat in a period than they can reproduce, they experience cold stress (AWHONN et al., 2023), which requires them to use compensatory mechanisms (increased respirations and nonshivering thermogenesis) to maintain core body temperature. When a neonate experiences excessive heat loss, they use stores of energy to compensate and maintain core temperature in the normal range. An increase in metabolic heat production above the basal metabolism that is not associated with muscle activity is called nonshivering thermogenesis (NST) . This occurs mostly through metabolizing brown fat and, to a much lesser degree, through the metabolization of skeletal muscle, the liver, the brain, and white fat. Brown fat mass peaks at birth and decreases in size over the first few weeks of life. Its metabolism is initiated with a catecholamine release. A newborn’s responsiveness to the release of catecholamines is increased by cutting the umbilical cord. Cutting the cord, release of catecholamines, and the stimulation of brown fat tissue are the driving factors in neonatal thermogenesis (Dattani & Gevers, 2016).
The metabolic consequences of cold stress are increased oxygen and glucose requirements and decreased cardiac output causing a decreased pulmonary blood flow leading to pulmonary hypertension and decreased surfactant production. These consequences result from activation of the sympathetic nervous system and are potentially fatal if not caught and reversed in time. Because of these major metabolic changes, the neonate goes into respiratory distress, sometimes experiences intraventricular hemorrhage, and has a higher risk of mortality than newborns who have not experienced cold stress (AWHONN et al., 2023). Preterm neonates and those who experienced intrauterine growth restriction are at increased risk for cold stress and higher mortality due to their decreased adipose tissue, brown fat, and glycogen available for metabolism (Gardner, 2020).
Causes of Cold Stress
As discussed earlier, heat loss can occur in a neonate from four different mechanisms: evaporation, convection, conduction , and radiation. The ways in which a neonate can lose heat during the immediate care period are numerous, and only some of the most frequent are listed here. Through evaporation, the newborn loses heat quickly immediately post birth in the birthing room and must be dried vigorously by the nurse, wrapped in a warm blanket, or placed skin-to-skin with the birthing person. Heat loss can also be caused by newborn baths, and for this reason, it is generally recommended that the bath be given between 6 hours and 24 hours after birth, when the newborn has had multiple temperatures over 37.5° C (99.5° F). Baths should use warm water and be as short as possible. The nurse should plan to use appropriate rewarming measures after bathing, including skin-to-skin contact (New, 2019). Placing the crib too close to a drafty window or a cold wall accelerates neonatal heat loss, as does having a ceiling fan or circulating fan in the room.
Signs and Symptoms of Cold Stress
It is critical that the nurse be aware of the signs and symptoms of cold stress developing in the neonate so that they can recognize subtle changes. The most obvious sign is an axillary temperature reading below 36.5° C (97.7° F). (See Chapter 23 Newborn Assessment for a discussion of taking axillary temperatures in the newborn.) Neonates should have temperatures monitored often during the first hour after birth and every 4 hours after that. Beyond a low axillary temperature, a neonate experiencing cold stress will appear acrocyanotic, irritable, and hypotonic (Gardner, 2020). Additionally, the neonate will become hypoglycemic due to the increased metabolic demand on their body brought on by the cold stress.
Neonatal Cold Stress: Management
Management of hypothermia in a neonate is vital to keep them thermodynamically stable. The nurse caring for the neonate needs to know the steps to take to correct hypothermia before it escalates to cold stress.
1. Radiant Warmer : Warmers limit heat loss because of ease of access and constant temperature monitoring and control. During the immediate care period, neonates are subjected to many interventions that require them to be away from the birthing person and away from skin-to-skin temperature protection. Therefore, anytime the neonate is away from that protection, they should be wrapped in warm blankets, wear a hat, and be placed under the radiant warmer .
2. Handling and Temperature: Neonate temperatures should be monitored hourly for the first 4 hours post birth and then every 4 hours after that if they are stable. If they are not stable, temperatures need to be monitored more frequently while corrective measures are being taken. Temperatures should be taken before an intervention is done and then after. If the nurse uses corrective measures to increase a hypothermic neonate’s temperature, they should always recheck the temperature and document any change.
3. Glucose monitoring: Infants that are small-for-gestational age or large-for-gestational-age, will need blood glucose monitoring every 4 hours. Knowing that metabolic requirements increase for neonates in hypothermic states, the nurse will recognize that if a neonate is hypoglycemic, the nurse should also check their temperature.
4. Clothing: Neonates are sensitive to changes in airflow and evaporation, as well as changes in environment, and should be dressed and swaddled appropriately in the first 28 days. Hats, T-shirts or footed pajamas, and warm blankets are the very least they should be dressed in to ensure temperature regulation.
5. Respiratory Changes: Two of the first signs of cold stress are irritability and changes in respiration, so thorough and accurate assessment of the respiratory system is key to recognizing subtle changes in the neonate. Assessment of the respiratory system will be done hourly in the first 4 hours and after that every 4 hours until discharge. (Fellows, 2010)
Prevention and Management of Cold Stress
Prevention of cold stress is the focus for the nurse and includes keeping the neonate dry after birth and wrapped in warm blankets or in skin-to-skin contact with the birthing person if possible. If the newborn’s temperature is unstable with skin-to-skin contact, the nurse will swaddle the newborn in warm blankets and place them under the radiant warmer, rechecking their temperature in 30 minutes. If the neonate is already experiencing cold stress, the nurse will check the blood glucose of the newborn with a point of care machine and work diligently to rewarm the baby with swaddling and radiant warmer. Other interventions include ensuring that the newborn is dry and has a hat on their head, that all steps of the ten-step warm chain have been followed, and that a health-care provider has been notified of this critical change for the newborn.
When to Call for Help
The nurse will call the pediatrician or the NICU for help if, upon recheck in 30 minutes, the newborn’s temperature is still below 36.5°C; the infant loses consciousness; or the infant experiences respiratory distress signs, such as grunting, nasal flaring, retractions, tremors, or jitteriness along with inconsolable crying. Close glucose monitoring may be required for at-risk neonates because symptoms can be subtle.