Which finding is indicative of hypothermia of the preterm neonate?

Physiology of thermoregulation

Every human, regardless of age, has the ability to maintain a core body temperature within a specific range in order to preserve good body function. Humans are homeotherms by nature; they produce their own temperature and maintain it within normal levels by balancing their heat loss and heat production according to their needs [Gardner et al, 2011]. This ability of balancing body temperature is defined as thermoregulation. In contrast, difficulty in maintaining this balance is characterised as ineffective thermoregulation [Carpenito-Moyet, 2008]. Newborn babies have a greater difficulty maintaining their body temperature than adults and children. This is seen most frequently and at the highest degree in premature babies [Kumar et al, 2009; Gardner et al, 2011]. Preterm infants have a greater need for an environment with a neutral temperature due to their ineffective thermoregulation [Lunze and Hamer, 2012]. Once born, the baby is exposed to an atmospheric temperature [about 25°C]—significantly below intrauterine temperature [approximately 37°C]. This ‘colder’ environment, in combination with the newborn's wet body, results in a heat-loss of between 0.1°C to 0.3°C per minute and of up to of 0.2°C to 1°C per minute [where there are no precautions taken regarding neonatal thermal protection after birth] [Waldron and MacKinnon, 2007; Kumar et al, 2009]. This cold-shock stimulates the newborn to commence two main physiological mechanisms in order to produce heat and to maintain its temperature at normal levels [Kumar et al, 2009].

Extrauterine thermogenesis

The first mechanism allows the newborn to activate non-shivering thermogenesis in order to produce heat by using brown adipose tissue. The second mechanism is peripheral vasoconstriction whereby the blood vessels located peripherally in the newborn's body constrict in an attempt to prevent further heat loss [Polin et al, 2011]. While Hillman et al [2012], Lunze and Hamer [2012], and Polin et al [2011] suggest that shivering thermogenesis can occur in newborn babies, they consider it to be of ‘secondary importance’ and to rarely occur. Regardless of the type of thermogenetic mechanism, it is known that preterm or low birth weight babies have a significantly higher risk of poor thermoregulation and increased heat-loss, due to their reduced body fat storages, thinner skin, and increased body surface compared to body mass [Waldron and MacKinnon, 2007].

Neonatal heat-loss mechanisms

There are four basic mechanisms that cause heat loss from the newborn; evaporation, radiation, conduction, and convection [World Health Organization [WHO], 1997; Waldron and MacKinnon, 2007; Blackburn, 2008; Soll, 2008; Davis, 2009; Kumar et al, 2009]. These mechanisms may cause heat-loss regardless of the type of birth, gestation or birth environment, and awareness of their effects by health professionals is critical for the prevention and management of neonatal heat-loss.

Evaporation occurs when the amniotic fluid covering the newborn and the mucosa of the respiratory tract of the baby, vaporise following birth [Blackburn, 2008; Davis, 2009]. Radiation occurs when heat is lost from the baby to any surface surrounding it that is not directly connected to it, including walls or any surfaces close to the baby which are colder than the baby [Davis, 2009].

Radiation can also positively affect the temperature of a newborn with heat being gained from sources that radiate heat, such as heat lamps [Soll, 2008]. Like radiation, conduction can result in both heat-loss, when the warm, naked body of the baby is placed on a colder surface; and heat-gain when a baby is placed on a warmer surface, for example on its mother's chest during skin-to-skin contact [Durand et al, 1997; WHO, 1997; Galligan, 2006; Gouchon et al, 2010; Lunze and Hamer, 2012] Convection refers to the heat-loss from the baby's body through the surrounding air [Kumar et al, 2009]. This heat-loss can occur in either a passive or forced way. Passive convection happens when heat escapes from the skin surface of the baby. Forced convection occurs when an air current passes over the baby's body, removing the heat in a faster and more aggressive way [Blackburn, 2008].

The ability of a baby to create [thermogenesis] and regulate its body temperature [thermoregulation] are not always sufficient to enable the maintenance temperature within the accepted ‘normal’ range. If not prevented and/or managed, temperature loss in a newborn will result in neonatal hypothermia with serious and potentially fatal consequences.

Neonatal hypothermia

Neonatal hypothermia is a pathological condition where the temperature of the newborn drops below the recommended normal temperature ranges. However, no agreement exists within the literature as to a standard accepted normal temperature range with different values identified in different studies [Kumar et al, 2009].

The lack of an agreed normal temperature value results in a range of temperatures being accepted as ‘normal’ by various authors with neonatal norms ranging between 36 and 37.7°C, depending on the geographical location of the study as well as the environmental/seasonal conditions [Lunze et al, 2013]. In the absence of agreement among researchers, WHO guidelines are used to describe the ‘normal’ ranges of neonatal normothermia and hypothermia.

WHO [1997] considers a newborn to be normothermic when its temperature is between 36.5 and 37.5°C and hypothermic, when its temperature is below the spectrum mentioned above. In order to facilitate the diagnosis and management of hypothermia, WHO has divided this classification into three well defined categories.

These categories are [WHO, 1997]:

While the WHO categories are useful, it does not identify the body site associated with each temperature category and this presents further challenges with the potential to result in a degree of confusion for both researchers and health professionals. Rectal temperature is approximately 0.5–1°C higher than oral and/or axillar temperature and is generally considered more representative of the core temperature [Ganong, 2005]. However, given the risks associated with the measurement of rectal temperature in newborn babies [i.e. rectal perforation and nosocomial infections], it is not recommended for newborn infants [Hertz, 2005]. WHO recommend that neonatal temperature is measured at the axilla and recommends that rectal temperatures are only measured in the event of diagnosed neonatal hypothermia. While the above classification is used by some maternity hospitals internationally, its use is still narrowly spread. Kumar et al [2009] identified that of 20 studies reviewed, only seven used the WHO classification system. This inconsistency of classifying neonatal hypothermia may lead to under-recognition as well as inadequate management of newborn hypothermia [Kumar et al, 2009]. It is essential, therefore, that guidelines are developed for the classification, prevention and management strategies for neonatal hypothermia, and that they are implemented by all medical, nursing and midwifery staff in each hospital.

Risk factors for neonatal hypothermia

Neonatal hypothermia is related to a number of risk factors, which are categorised by Lunze et al [2013] into four main groups: environmental, physiological, behavioural and socioeconomic. Environmental risk factors are related to the geographical area in which the baby is born, as well as time of the year [seasons] and room temperature at the time of birth [WHO, 1997; Lunze et al, 2013]. While the prevalence of neonatal hypothermia is higher during the winter season, being born during the summer months or in a warm tropical climate, does not automatically eliminate the risk of a baby becoming hypothermic and highlights the need for continued vigilance to prevent, identify and manage neonatal hypothermia.

Physiological risk factors mainly pertain to neonatal issues such as prematurity, low birth weight and intrauterine growth restriction. Babies who are ‘small for dates’ or hypoglycaemic are also at increased risk for hypothermia [Kumar et al, 2009; Gardner et al, 2011; Lunze et al, 2013].

Behavioural risk factors are considered to be any non-evidence based practices, sometimes undertaken for cultural reasons, which may potentially cause a reduction in the baby's temperature resulting in hypothermia. Two examples of such practices are: bathing of the newborn immediately after birth, and/or massaging the baby with essential oils after birth [Bergstrom et al, 2005; Onalo, 2013].

Socioeconomic factors can also contribute to neonatal hypothermia. Socially mothers who are either young and inexperienced, or multiparas who are minding many children; babies born in families with a low income and/or from resource poor countries are also more likely to be socially and economically disadvantaged. Health professionals in resource poor countries may not have access to knowledge and/or best available evidence or other resources to support best practice, therefore babies born in these countries may also be at risk of neonatal hypothermia [Lunze et al, 2013].

Effects of hypothermia on the newborn

Hypothermia in a newborn is detected through a number of objective signs resulting from the impact on multiple body systems; cardiopulmonary [bradycardia, tachypnea, apnoea]; the central nervous system [lethargy, distress, poor feeding], and the vascular system [peripheral vasoconstriction, acrocyanosis, cold extremities] [Waldron and MacKinnon, 2007; Onalo, 2013]. Disturbance associated with the baby's metabolism can also result in symptoms of hypoglycaemia, hypoxia and eventually metabolic acidosis [Waldron and MacKinnon, 2007; Freer and Lyon, 2011]. Failure to diagnose and manage hypothermia may lead to chronic symptoms such as weight loss and/or slow weight gain, with the eventual outcome of negatively impeding normal growth and development [UNICEF, 2004]. Other complications associated with hypothermia are severe sepsis and neonatal death [WHO, 1997; Mullany, 2010; Lunze and Hammer, 2012; Onalo, 2013].

Prevention and management of neonatal hypothermia

There is a substantial body of literature suggesting methods for preventing neonatal hypothermia both for term and pre-term infants, whether born in high or low resource countries [WHO, 1997; Knobel et al, 2005; Soll, 2008; Holtzclaw, 2008]. The majority of the literature describes how to prevent hypothermia by focusing on improving environmental factors. In particular there is agreement that the birth room temperature is required to be a minimum of 25°C for term babies and 26–28°C for pre-term babies [WHO, 1997; Knobel et al, 2005]. Soll [2008] suggests that delivery rooms tend to be kept at a temperature, while pleasant for health professionals and mothers, does not adequately consider the needs of newborn babies. Raising awareness among health professionals about the effects of a cold room on newborns and the requirement to maintain room temperature above 25 or 26°C, is a simple, yet critical intervention to help prevent neonatal hypothermia. The development and implementation of protocols and education seminars to promote awareness and enhance evidence-based knowledge is essential in all birth environments [Nirmala et al, 2006; Chomba et al, 2008; Kumar et al, 2009; Sobel et al, 2010]. However, maintaining a high room temperature alone is insufficient, as prevention of hypothermia due to environmental factors also includes techniques of passive and active warming [Holtzclaw, 2008].

Passive warming includes all man-made tools that act as barriers to heat loss. The literature identifies two fundamental heat loss barrier tools; polyurethane caps and plastic bag wraps.

The majority of these studies have examined the effects these tools have in the prevention of hypothermia in pre-term babies [Roberts, 1981; Gathwala et al, 2010; Trevisanuto et al 2010; Khairina et al, 2011; Leadford et al, 2013]. Active warming, refers to the methods used to warm the baby in a direct way. Two active warming methods identified in the literature including radiant heaters and skin-to-skin contact [Holtzclaw, 2008]. Radiant warmers and exothermic mattresses are used either during the resuscitation of the newborn or to warm up a cold baby. The first device spreads heat through radiation while the second group of devices heats the baby through conduction. Skin-to-skin contact is an alternative and natural way of active warming and one that has benefits for both baby and mother.

Skin-to-skin contact

Skin-to-skin contact or Kangaroo care is a well-explored practice over the past 25 years [Flynn and Leahy-Warren, 2010; Lunze et al, 2013] whereby the newborn is positioned in an upright position, between its mother's breasts, wearing only a nappy and a hat [Nirmala et al, 2006; Gabriel et al, 2009; Takahashi et al, 2011]. This approach has been recommended for its ability to maintain the baby's temperature within normal parameters [Carfoot et al, 2005; Hunt, 2008; Gouchon et al, 2010; Gabriel et al, 2011], and to warm up babies with mild hypothermia [WHO, 1997]. Among the recognised benefits of skin-to-skin contact is its ability to promote early initiation of breastfeeding and to prolong its duration [UNICEF, 2004; Carfoot et al, 2005; Hunt, 2008; Bramson et al, 2010; Gouchon et al, 2010; Gabriel et al, 2011; Suzuki, 2013; Svensson et al, 2013] skin-to-skin contact also improves the heart rate and oxygen saturation levels of the baby [Nirmala et al, 2006; Hunt, 2008; Nolan and Lawrence, 2009; Takahashi et al, 2011] and allows earlier brain maturity in premature infants in comparison with premature infants who had no skin-to-skin contact [Kaffashi et al, 2013].

The majority of the research examining skin-to-skin contact involves babies born vaginally with only two papers focusing on full-term babies' temperatures born after caesarean section [Nolan and Lawrence, 2009; Gouchon et al, 2010]. The first study was an experimental trial in which 34 mother and baby pairs were randomly selected and separated into two groups [skin-to-skin contact group and routine care [RC] group] after elective caesarean section. The babies' temperatures were checked with an infra-red thermometer half hourly for 2 hours post-birth and the mother's temperature was measured prior to and following the surgical procedure and while holding their babies. The findings demonstrated that babies who had skin-to-skin contact were not at risk of hypothermia when compared to the routine care baby group [Gouchon et al, 2010]. However, a careful examination of the documented temperatures of babies and mothers in this study indicates that, in fact, the documented temperatures were indicative of mild-to-moderate hypothermia [as defined by WHO [1997]]. Furthermore, some practices used in this study are not recommended for application by WHO. Examples include: bathing babies after birth, delivery room temperatures less than 25°C [mean of 22°C], and skin-to-skin contact was not always commenced after birth. As a result, difficulties exist with this study in demonstrating that skin-to-skin contact following caesarean section maintains neonatal temperature within the range defined as normal by WHO [1997]. Furthermore, any connection between low maternal temperatures with the prevalence of hypothermia in infants is not explored.

Nolan and Lawrence [2009] reviewed a sample of 50 mother–baby pairs which were separated evenly into a skin-to-skin contact group and a RC group. Infants' temperatures were obtained from medical record at 0.5, 1 and 2 hours postbirth; however, 30% of temperatures were missing. This study demonstrated that babies in the skin-to-skin contact group had higher mean temperatures than the RC-group babies, although this temperature difference was not statistically significant. Maternal temperature and delivery room temperature were not included in this study thus no association can be made between maternal temperature and that of the baby during skin-to-skin contact. The authors of both articles suggest further research is required to investigate this subject fully [Nolan and Lawrence, 2009; Gouchon et al, 2010]. Given that caesarean section rates have almost doubled since the previous WHO report in 1985, there is also a significant lack of evidence supporting the benefits of skin-to-skin contact in preventing/managing neonatal hypothermia following caesarean section, therefore further research is required taking into consideration these new circumstances [WHO, 2010].

Conclusion

Neonatal hypothermia is a major risk factor to neonatal morbidity and, in extreme cases, mortality [Kumar et al, 2009]. Newborns are at risk of hypothermia irrespective of their nationality, sex and gestation. Unlike adults and children, newborn infants have greater difficulty maintaining their body temperature.

Neonatal hypothermia is a condition that has potentially life threatening effects for the newborn infants worldwide. A significant challenge in research and practice pertaining to neonatal hypothermia is the absence of an agreed and internationally accepted definition of neonatal normothermia and hypothermia. The failure to have an agreed standard for temperature in neonates results in continuing confusion about how hypothermia is defined, when it should be diagnosed and when intervention are required to mitigate its deleterious effects. Agreement is also required relating to the site of temperature measurement and type of thermometer used. Therefore, a suggestion emanating from this review is that in the absence of an agreed definition of neonatal normothermia and hypothermia, future research should adopt the existing WHO classification and categorisation. Doing so will ensure greater consistency in terms of measurement and interpretation of research results and their translation into practice.

Preventing hypothermia by focusing on improving environmental factors has been identified as a simple and achievable yet critical intervention. Further management includes maintaining delivery room temperature between a minimum of 25°C for term babies and 26–28°C for pre-term babies as well as ensuring that all health professionals are aware of and intervene to ensure adequate temperature is maintained is required.

One of the suggested practices to prevent and or treat mild hypothermia in newborn infants is skin-to-skin contact. However, the available research regarding skin-to-skin contact and hypothermia in infants post caesarean section is limited. Furthermore, the connection between maternal hypothermia, skin-to-skin contact and neonatal hypothermia after caesarean section has not been explored in any depth and needs to be examined [Horns et al, 2002; Fallis et al, 2006; Yokoyama et al, 2008; Nolan and Lawrence, 2009; Gouchon et al, 2010]. Cold adversely impacts the health and wellbeing of newborn infants and understanding its causes and how to prevent it is an essential part of the midwife and doctor's role around the time of birth. It is imperative that we understand the process and what steps can be taken to prevent hypothermia and in doing so, provide a safe and secure environment into which a baby can be born.

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