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Neonatal thermoregulation

By Dr. Namrata Todurkar


Maintaining a normal temperature is one of the most important challenges that a newborn must face after delivery. Thermoregulation is the ability to balance heat production and heat loss in order to maintain body temperature within a certain normal range. The American Academy of Pediatrics (AAP) and the World Health Organization (WHO) define normal axillary temperatures to be between 36.5°C and 37.5°C. Thermoregulation is essential for the survival of a newborn and more so for a preterm infant. This blog post will discuss the importance of thermoregulation and the various ways in which the family can contribute towards prevention of temperature fluctuations.


Before going into further details, it is important to differentiate ‘core temperature’ from ‘peripheral temperature’. ‘Core temperature’ is measured from the rectum, the ear canal (ear drum/ tympanic membrane), or the food pipe (esophagus). Such measurements are invasive and not commonly used. ‘Peripheral temperature’ is measured from the skin (ex: axilla, forehead) or the oral cavity. As expected, core temperature is higher than peripheral temperature and, in this blog post, we will refer only to peripheral temperature. It is commonly used and easy to measure with a simple digital thermometer.


Hypothermia: Hypothermia is defined as a temperature below 36.5°C. There are various categories of hypothermia depending on its severity (cold stress, moderate and severe hypothermia). It is surprising to know that hypothermia can cause breathing difficulty, low blood pressure, lethargy, mottling of the skin, and feed intolerance, and if prolonged, may lead to long-term issues such as growth failure and poor neurodevelopment outcomes.


Maintenance of temperature is an uphill battle for a preterm infant. When left unattended, they use all their resources to generate heat and falter in other essential tasks like breathing, maintaining circulation, and digesting feeds. When heat loss exceeds the newborn’s ability to produce heat, its body temperature drops below the normal range. The smaller or more premature the newborn is, the greater the risk of heat loss; therefore, these babies require a constant thermal-neutral environment like the incubator.


The following characteristics put preterm newborns at a greater risk of heat loss:


1. A large surface area-to-body mass ratio

2. Decreased subcutaneous fat

3. Greater body water content

4. Immature skin leading to increased evaporative water and heat losses

5. Poorly developed metabolic mechanism for responding to low temperatures (e.g., no shivering)


Before birth, the fetal temperature is dependent on the mother as heat is transferred to the fetus via the placenta and the uterus, resulting in a 0.3 degrees C to 0.5 degrees C higher temperature than that of the mother. At birth, the neonate rapidly cools in response to the relatively cold extrauterine environment. In order to survive, the neonate must accelerate heat production. During the first 10 to 20 minutes, the newborn may lose enough heat for the body temperature to fall by 2-4°C if appropriate measures are not taken.


There are four ways in which a newborn loses body heat:


Evaporation: when amniotic fluid evaporates from the skin. Evaporative losses are unmeasurable/ insensible (from skin and breathing). This is the greatest source of heat loss at birth.


Conduction: when the newborn is placed naked on a cooler surface, such as a table, scale, cold bed, transfer of heat takes place between the two, resulting in hypothermia of the infant.


Convection: When the newborn is exposed to cool surrounding air or to a draft from open doors, windows, or fans, the transfer of heat from the newborn to the circulating air takes place.


Radiation: when the newborn is near cool objects, walls, tables, and cabinets, without being in contact with them, transfer of heat takes place between the two solid surfaces even when they are not touching. This is the greatest source of heat loss after birth.


As noted earlier, most cooling of the newborn occurs immediately after birth. The temperature of the environment during delivery and the postnatal period has a significant effect on the risk to the newborn of developing hypothermia. Having a preterm birth in a tertiary care referral hospital is ideal. However, preterm births have happened in the middle of a vacation, in homes, hotels, flights, and in ambulances. As parents, is there anything that you can do to ensure thermoregulation?


How to prevent hypothermia at birth?


1. Place the infant on the mother’s body immediately after delivery.

2. Delay cord clamping by 30-60 seconds.

3. Place a cap on the baby’s head.

4. Place the baby’s body (below neck) in a clean plastic bag.

5. Use warm towels to cover the baby.

6. Perform initial steps of resuscitation (stimulation, clearing secretions and positioning airway) on mother’s body.

7. Allow for skin-to-skin care for as long as possible

8. If the baby does not respond to the initial steps of resuscitation, transfer to a radiant warmer with cap and a plastic bag on.


How to prevent hypothermia in NICU?


1. Use of incubators with advanced temperature and humidity control.

2. Skin to skin care (kangaroo care)

3. Use of cap, mittens, and socks when outside the incubator.

How to prevent hypothermia after discharge?

1. Feed regularly, even at night.

2. Use cap, mittens and socks always.

3. Dress appropriately for the weather.

4. Skin to skin care.

5. Place the baby’s bed in a draught free area.


Red flag signs associated with hypothermia:


1. Lethargy

2. Poor feeding

3. Unresponsiveness

4. Abnormal skin color like mottling, bluish discoloration.

5. Abnormal body movements (seizures)

6. Fast breathing.

7. Abdominal swelling

8. Redness and pus discharge from the umbilicus


Identifying the cause of hypothermia is as important as treating it. Hypothermia can predispose an infant to infection and at the same time be a manifestation of a lingering sepsis. Treating hypothermia is essential in order to avoid serious and potentially life-threatening complications. Increased cellular metabolism takes place as the newborn tries to stay warm, leading to increased oxygen consumption, which puts the newborn at risk of hypoxia (low oxygen level in blood), cardiorespiratory complications (low blood pressure, poor heart function), and acidosis (increased acid accumulation in blood). These newborns are also at risk for low blood sugar level because of the increased glucose consumption necessary for heat production. Neurological complications, jaundice, blood clotting disorders, and even death may result if the untreated hypothermia progresses.


The mainstay of care is to maintain the newborn in a neutral thermal environment, which ensures minimal metabolic activity and oxygen consumption are required to conserve body temperature. Incubators are now specifically designed to minimize losses by radiation, convection, conduction, and evaporation whilst allowing clear visibility and access to the patient. Increased vigilance regarding maintaining temperature control should be instigated for any transfers. Re-warming after a period of hypothermia should be well controlled. Ideally, hospitals that care for sick and low birth weight newborns should have additional equipment such as overhead heaters, heated mattresses, incubators, and low-reading thermometers that read temperatures down to 25°C.


Therapeutic Hypothermia:


While we have discussed everything bad about hypothermia, there are a few situations where hypothermia is used as a therapy. In infants born after 35 weeks of gestation, therapeutic hypothermia is used to decrease metabolism, preventing further injury to a brain that has suffered birth asphyxia. Although it is not free of complications, the overall neurological outcome in such infants is better with the use of therapeutic hypothermia. Its use in preterm infants is not yet approved.


Hyperthermia: Hyperthermia is defined as a body temperature above 37.5°C. All infants with hyperthermia/ fever need immediate medical attention in order to rule out serious medical conditions, the most common being sepsis. Regardless of cause, hyperthermia can have detrimental consequences


Causes of hyperthermia:


1. Infection/ Sepsis

2. Dehydration

3. Overheating from incubators, radiant warmers, or ambient environmental temperature

4. Maternal fever

5. Phototherapy lights

6. Excessive bundling or swaddling

7. Neurological disorders (i.e., asphyxia)


Summary:

Temperature regulation may seem to be a simple aspect of neonatal care. However, it can be a game changer for preterm infants. Having knowledge about the physiology of thermoregulation helps rationalize the various steps that the NICU team takes to ensure a normal temperature in every baby.

Dr. Namrata Todurkar, MBBS, MD (Pediatrics), DNB (Pediatrics). Fellowship in Neonatology from National Neonatology Forum India. Fellow in Neonatal-Perinatal Medicine at the University of British Columbia. Areas of interest: Neonatal nutrition, Fluid and Electrolyte Management, Inborn Errors, Neurodevelopmental follow-up of preterm infants. Dr. Todurkar is a volunteer blogger at CPBF.


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