Keeping Baby Warm: Thermoregulation in the Neonate
Published: 27 September 2020
Published: 27 September 2020
So, what is a thermoneutral environment and how can it be created and maintained?
Thermoregulation is the ability to balance heat production and heat loss to maintain steady, normal body temperature, with a stable metabolic state where minimal rates of oxygen consumption or energy expenditure occur (Ahern et al. 2017).
To put it more simply, a neutral thermal environment is the optimum environmental temperature to ensure an infant has the lowest oxygen and energy expenditure whilst maintaining a normal body temperature. Each infant has their own neutral thermal environment depending on their birth weight, gestation and whether or not they are clothed (North Devon Healthcare NHS Trust 2018).
An ideal thermoneutral environment is achieved when infants can maintain their core body temperature at rest between 36.5℃ and 37.5 ℃ (Ahern et al. 2017). Too much heat, or too little, can result in thermal stress in the form of hyperthermia, or more commonly, hypothermia or excessive heat loss.
Without the ability to maintain a steady body temperature, cold stress and hypothermia can occur, leading to serious metabolic problems and the potential risk of morbidity or mortality (Çınar & Filiz 2006).
Some of the reasons why babies are prone to poor thermoregulation at birth include:
(Ahern et al. 2017)
Although other methods of temperature assessment exist, Friedrichs et al. (2013) recommend left axillary temperature measurement in the full-term newborn infant for the first few days of life as a safe and accurate alternative to taking rectal temperatures.
The standard range of body temperatures for a healthy term newborn is:
(North Devon Healthcare NHS Trust 2018)
That said, Waldron and MacKinnon (2007) note that The World Health Organisation has slightly different parameters, defining mild hypothermia as a core body temperature of 36°C to 36.4°C, moderate hypothermia as 35.9°C to 32°C and severe hypothermia as less than 32°C.
Research conducted by Takayama et al. (2000) also refines these measurements by suggesting that although the average birth temperature of newborn infants is 36.5°C, the mean increases with postnatal age, rising 0.2°C by 2 to 3 hours after birth and 0.3°C by 15 to 20 hours.
Axillary temperature was also found to be linked to birth weight and the presence of maternal fever, though there was no link to the type of surrounding environment or the time of birth.
Takayama et al. (2000) also suggest that given the frequency of below-normal body temperature without any associated illness, the reference range for newborn temperatures should be expanded to include lower temperatures.
Hypothermia or cold stress is known to occur via four principal methods:
(Ahern et al. 2017)
It’s well known that hypothermia has a direct relationship with increased mortality and morbidity, with a 28% increase in mortality for each 1 ºC drop in temperature. Rapid heat loss of up to 1ºC per minute can occur in infants nursed in an inappropriate environment, highlighting the importance of accurate temperature measurement.
In particular, excessive heat loss can lead to acidosis due to the metabolism of fatty acids, as well as increased oxygen consumption leading to episodes of hypoxia. Other complications caused by hypothermia include increased glucose uptake which may result in hypoglycaemia as well as postnatal weight loss, or failure to gain weight.
An ideal thermoneutral environment is achieved when infants can maintain a core temperature at rest of between 36.51ºC and 37.51ºC, but for certain infants this may require extra monitoring and intervention. Those most at risk include:
(Ahern et al. 2017)
Brown fat makes up approximately 1.4% of the body mass of healthy infants weighing more than 2 kg. It is mainly found in nuchal subcutaneous tissue around the kidneys, the mediastinum and interscapular regions.
When their temperature falls between 36°C and 35°C, newborn infants peripherally vasoconstrict and initiate a non-shivering thermogenesis of brown adipose tissue. However, as brown fat only starts to form from 26 weeks gestation and development stops post-delivery, it can leave many preterm babies at greater risk of cold stress. With continued hypothermia, stores of brown fat can become depleted, resulting in hypoxia and hypoglycaemia (Waldron and MacKinnon 2007).
Premature infants and those suffering intrauterine growth restriction are particularly at risk of hypothermia as they have less brown fat stores, decreased fat for insulation, decreased glycogen stores, immature skin that increases water loss, poor vascular control, a slower metabolism and a narrower range of thermal control (Waldron and MacKinnon 2007).
Some of the signs that a preterm infant is having difficulty keeping warm include:
(North Devon Healthcare NHS Trust 2018)
Temperature monitoring in the newborn is a well-researched and standard procedure for all infants in the first few days of life. For premature babies or those born with growth restriction, it becomes even more important as the risk of hypothermia and cold stress is increased.
Yet, with care and interventions to prevent heat loss such as skin-to-skin contact, coverings such as wraps and hats, or incubator care for those who need it, the thermoneutral environment can easily be maintained.
Anne is a freelance lecturer and medical writer at Mind Body Ink. She is a former midwife and nurse teacher with over 25 years’ experience working in the fields of healthcare, stress management and medical hypnosis. Her background includes working as a hospital midwife, Critical Care nurse, lecturer in Neonatal Intensive Care, and as a Clinical Nurse Specialist for a company making life support equipment. Anne has also studied many forms of complementary medicine and has extensive experience in the field of clinical hypnosis. She has a special interest in integrating complementary medicine into conventional healthcare settings and is currently an Associate Tutor, lecturing in Health Coaching and Medical Hypnosis at Exeter University in the UK. As a former Midwife, Anne has a natural passion for writing about fertility, pregnancy, birthing and baby care. Her recent publications include The Health Factor, Coach Yourself To Better Health and Positive Thinking For Kids. You can read more about her work at www.MindBodyInk.com. See Educator Profile