Chapter 42 Thermoregulation
Introduction
Practitioners involved in the care of the newborn need to master the art of thermoregulation to support and maintain a suitable environment for the baby’s wellbeing, achieve safe and competent practice, and provide information and advice for parents and other relevant persons involved in the baby’s care.
No newborn baby can afford the effects of cold stress. Those least able to tolerate hypothermia include the late preterm and/or growth-restricted and ill babies. Maintenance of an optimal thermal environment, which studies have shown to influence growth and survival, is a vital part of neonatal care. There is a rich history underpinning thermoregulation, including different infant care practices and incubator development (see website).
Physiology of thermoregulation
Information from temperature receptors distributed widely in many parts of the body is transmitted to:
When the body temperature rises, the typical adult human autonomic response is peripheral vasodilatation and sweating to cool the skin; the behavioural response is to seek a cooler environment and remove clothing. When body temperature falls, the typical responses are peripheral vasoconstriction and shivering, the need to seek warmth and put on more clothing.
Normal thermoregulatory function ensures that over a wide range of ambient temperatures, body core temperature is controlled at a relatively stable level – generally between 36.5°C and 37.5°C (Blackburn 2007). The ambient temperature range over which normal body temperature is achieved with minimal activation of metabolic and evaporative process is called the thermoneutral zone. For a naked adult, this zone is between approximately 27°C and 33°C.
Deviations of body temperature may take three forms:
Fetal perspective
During pregnancy, the heat generated by the mother increases by 30–35%, thus the woman can be expected to have a temperature of 37.5°C during pregnancy. This is due to the effect of progesterone on metabolism and the basal metabolic rate (BMR), leading to the mother’s perception of being more comfortable in a cool environment. In the maternal system, there is an increase of four to seven times the cutaneous blood flow and activity of sweat glands.
Fetal temperature is tightly linked to the maternal temperature regulation and cannot be autonomously controlled by the fetus (the heat clamp). Fetal temperature is generally about 0.3–1.0°C above maternal body temperature (Liebeman et al 2000) – usually 37.6–37.8°C (Blackburn 2007, Polin & Fox 2004).
The placenta is an effective heat exchanger for the fetus, and thermoregulation is influenced by:
Some fetal generated heat is dissipated into the amniotic fluid via the umbilical cord (Hartman & Bung 1999, Blackburn 2007). Heat transfer is facilitated by the maternal–fetal gradient, apparent when the mother is exposed to changes in temperature, either during exercise, illness or through environmental factors such as taking a sauna.
Unstable uterine temperature, especially in the embryological state, can cause teratogenic abnormalities in the newborn (Artal & O’Toole 2003). In these cases the gradient may be reversed or reduced, which can lead to the fetal temperature rising. Changes in fetal temperature tend to be slower than maternal changes, owing to the insulatory effects of the amniotic fluid (Blackburn 2007).
Neonatal perspective
Thermoregulation is a critical physiological function in the neonate – closely linked to survival and health status. Birth precipitates the baby into a harsh and cold environment requiring major physiological adaptations and changes, including thermoregulatory independence. Newborn babies are less efficient than adults in the ability to thermoregulate.
The ability to generate heat depends on body mass and environmental heat loss, a large surface-area-to-mass ratio (about three times higher than in the adult) leading to difficulty in maintaining body temperature in a cold environment.
Babies with a low body mass are more at risk. Although full-term babies have control over peripheral vascular circulation equal to adults, the autonomic thermoregulatory responses are not fully developed. The healthy baby can increase basal heat production by 2.5 times in response to cold within 1–2 days of birth, though less so in the first 24 hours. Newborn babies are rarely able to shiver and the increased heat comes from the noradrenergic lipolysis of the brown fat deposits characteristic of the neonate and activation of specially adapted mitochondria in the brown fat to produce heat.
The most dangerous time for the newborn to lose heat is during the first 10–20 minutes of life. If measures are not taken to halt heat loss, the baby becomes hypothermic (temperature <36.5°C) soon after birth. A premature or sick baby who becomes hypothermic will be at risk of developing health problems and of dying (CESDI 2003) but the chances of survival are greatly increased if the temperature stays above 36°C. Birth should always take place in an environmental temperature above 25°C.
Hyperthermia (temperature >37.5°C) can occur and in extreme cases can cause death within the first 24 hours after birth. Hyperthermia increases the metabolic rate, leading to increased oxygen and glucose consumption plus water loss through evaporation. This causes hypoxia, metabolic acidosis and dehydration. A core temperature above 42°C may lead to neurological damage (WHO 1994).
Hyperthermia can be caused by infection; it is not possible to distinguish between infection and environmental factors by measuring the body temperature or by clinical signs. Therefore, a temperature above 37.7°C in the newborn is a deviation from normal and the baby must be urgently referred to the neonatologist for assessment, diagnosis and management.
Internal and external gradients
The external and internal gradients are interdependent. The internal gradient is the temperature differential between the core of the body and the skin and results in the transfer of heat from within the body to its surface. This process relies on an effective and extensive blood flow in capillaries and venous plexi influenced by tissue insulation provided by subcutaneous fat and the convective movement of heat through the blood. Heat conduction is under sympathetic control that results in changes in the skin blood flow by vasoconstriction and vasodilatation.
In the neonate, heat loss through this gradient is increased because of the thinner layer of subcutaneous fat and larger surface-to-volume ratio than in the adult (Blackburn 2007).
The external gradient results in heat loss from the body surface to the environment – the rate of heat loss is directly proportional to the difference between the temperature of the skin and that of the environment.
Heat transfer by the external gradient is increased in the neonate because of an increased surface area and thermal transfer coefficient. The neonate maintains temperature by means of the external gradient, that is, temperature skin changes, whereas the adult uses the internal gradient. This is especially significant for the preterm baby, for whom the control and effects of changes in the environment temperature are more profound.
Heat loss and gain
Babies at term are homeotherms; meaning having the ability to produce heat to maintain body temperature within a comparatively narrow range. The newborn cannot regulate body temperature as well as an adult can, and, when the environment becomes too cold or hot, is unable to respond and maintain temperature, therefore tolerating a limited range of environmental temperatures. Thermal stability improves gradually as the baby increases in weight and age.
There are four main routes of heat loss (Hammarlund & Sedin 1986):
Insensible water loss (that is, loss through the skin, urine, faeces and respiratory tract) may lead to significant heat loss – increased in preterm and low birthweight babies (Rutter 1985) because of the large ratio of surface area to body mass; limited subcutaneous fat; immature epidermal skin layer structure; and increased body water content. Risks rise in environments where insensible water loss is increased, as 0.58 kcal of heat is lost with each gram of water lost through evaporation (Hammarlund & Sedin 1986).
The appropriate temperature of a baby depends upon the baby’s age, gestation and weight. If left wet and naked, the newborn infant cannot cope with environmental temperatures of less than 32°C. If a thermometer is not available in a room, the environment must be assessed through personal comfort – what appears very warm and uncomfortable for an adult dressed in thin clothes with short sleeves is likely to be appropriate for the newborn.
Neonatal heat production
The hypothalamus and the autonomic and sympathetic nervous systems are important aspects of maintaining the temperature within narrow set limits of 36.5–37.5°C in the newborn (see website). Constant body temperature is achieved by a functioning neurological system balancing heat gain with heat loss effector systems.
In the newborn, heat production results from metabolic processes that generate energy by oxidative metabolism of glucose, fats and proteins. The organs that generate the greatest energy are the brain, heart and liver. To maintain a constant body temperature, heat loss from the surface of the body must equal heat gain.
In the baby, though the hypothalamus will receive cold alert messages from the skin, abdomen, spinal cord and internal organs, to regulate temperature stimuli from other areas of the body, the most sensitive receptors are contained within the trigeminal area of the face (Hackman 2001).
The responses of the skin surface are determined by:
In the human newborn, cooling of the skin has been shown to increase metabolic heat production without any change in the core temperature (Polin et al 2004).
Physical mechanisms include involuntary reactions, including shivering, and voluntary reactions involving muscular activity, through crying, restlessness and hyperactivity. These responses can be affected by anaesthetics, damage to the brain, muscle relaxants or sedative drugs.
The baby may generate heat by crying and become hyperactive when cold stress is severe enough to cause jitteriness, although shivering does not appear. If cold stress is not eliminated at this point, the baby may become extremely hypothermic, hypoglycaemic, hypoxic, acidotic and lethargic, and eventually death will ensue, caused by cold injury. The full-term baby can flex the body into the ‘fetal’ position, which provides some protection against cold stress, but the lack of muscle tone and flaccid posture of an immature or ill baby results in a higher heat loss. Babies can also reduce shunting of internal heat to body surfaces by constricting peripheral vessels.
Chemical or non-shivering thermogenesis is the process by which the neonate generates heat through an increase in the metabolic rate and through brown adipose tissue (BAT) metabolism. This process can be utilized by adults and neonates – in the adult the metabolic rate can be increased by about 10–15%, whereas the neonate can increase the metabolic rate by up to 100% (Cannon & Nedergaard 2004).
Heat production and brown adipose tissue (BAT)
A cold-stressed baby depends primarily on mechanisms that cause chemical thermogenesis. Neonatal heat production is mainly through non-shivering thermogenesis. When the baby becomes hypothermic, noradrenaline and thyroid hormones are released, inducing lipolysis in brown fat. This process can be affected by pathological events, including hypoxia, acidosis and glycaemia.
Brown adipose tissue is believed to constitute 2–7% of the newborn’s weight, depending on gestation and weight. Brown fat starts to be deposited in the fetus from 28 weeks’ gestation (Blackburn 2007). The brown adipocyte is uniquely suited to its role in newborn thermogenesis and differs from white adipose tissue because it is capable of rapid metabolism, heat production and heat transfer to the peripheral circulation.
The total amount of heat produced in the neonate is unknown, but may be up to 100% of its requirements (Blackburn 2007). The sympathetic nervous system stimulates the adrenal gland to release adrenaline, increasing the metabolism of brown fat and catecholamines and releasing the required glucose. The thyroid gland is also stimulated by the pituitary to release thyroid-stimulating hormone, also producing thyroxine (T4) – known to enhance heat production from BAT.
Heat production within BAT is not fully understood but it is known that BAT contains high concentrations of complex mitochondria, stored triglycerides, sympathetic nerve endings, and a rich capillary network to carry heat around the body. The presence of an uncoupling protein within the mitochondria of brown fat cells supports the combustion of fatty acids to produce heat.
BAT is especially prominent in the mammalian fetus, and anatomical distribution is important to its function. The largest mass of tissue envelops the kidneys and adrenal glands; smaller masses are present around the blood vessels and muscles in the neck and there are extensions of these deposits under the clavicles and into the axillae. Further extensions accompany the great vessels entering the thoracic inlet. The proximity of BAT to large blood vessels and vital vascular organs provides the ability for rapid transfer of heat to the circulation (Okken 1995, Polk 1988). The activation of BAT metabolism only occurs following birth. During intrauterine life, maternal prostaglandins and adenosine do not allow non-shivering thermogenesis to take place. With the clamping of the cord, this mechanism is blocked, enabling the hypothalamus to react to hypothermia (see website).
Feeding
From birth, the baby requires water, glucose and certain electrolytes. Calories are utilized for growth and energy in order to maintain body temperature and metabolism. The method of feeding the neonate, whether orally, by nasogastric tube or intravenously, and the frequency and volume of feeds depend on gestational age and physical condition. When gastric feeds have to be delayed for days and certainly if for more than a week, as in a case of a baby with severe respiratory distress, parenteral nutrition is required to ensure adequate calorific intake. Milk contains far more calories than dextrose given intravenously or orally (Klaus & Fanaroff 2001).
Drugs
Medication given to pregnant women can affect thermoregulation:
The role of the midwife
During pregnancy
Advice is provided regarding maintaining a stable temperature, especially during the first trimester of pregnancy when cell division and differentiation are ocurring. There is a higher risk of congenital fetal abnormalities in women who use a sauna, especially if this is a new activity to which the mother’s physiology has not adapted (Artal & O’Toole 2003, Cohen 1987, Smith et al 1988, Tikkenhan & Heinonen 1991). Care should be taken with other activities, such as hectic exercise, which significantly increase the maternal temperature.
Many women complain of heat during their pregnancy. The midwife can offer realistic and practical advice, including wearing natural fabrics, such as cotton, thin wool, silk or linen, and having cool baths/showers. The midwife should also assess the woman’s health, excluding infection and/or pyrexia, taking appropriate and swift action should either be identified.
Labour and birth
Midwives’ actions prior to labour and delivery determine the wellbeing of the newborn baby. This includes controlling the neonatal environment, ensuring that the delivery room (or home) is sufficiently warm. Monitoring and recording this 4-hourly is important. Attention must also be paid to the warmth of the towels used for wrapping the baby and other factors that may affect the neonate’s wellbeing, and any deviations from normal must be acted upon. A raised temperature may be an indication of infection or maternal ketosis (see Ch. 36) and may have implications for mother, fetus and neonate.
Waterbirth
Warm water as pain relief during labour and for giving birth is increasingly being chosen by women and it is believed that warm water can improve uterine perfusion and uterine contractions, leading to a less painful birth.
The temperature of the water must be comfortable for the woman and should not rise above 37°C as this may cause hypotension in the woman and reduced blood flow to the fetus. Therefore, water temperature should be frequently measured and recorded. When the baby is delivered in warm water it is believed that breathing will not be initiated until the baby’s head is lifted above the water. If the baby is asphyxiated or the water cold, then the baby may inhale some pool water (Gilbert & Tookey 1999).
Delivery room
Whether in home or in hospital, the midwife should ensure that all professionals, and the woman and her family, understand the importance of the birthing room being warm (temperature at 25–28°C) and free from draughts caused by open windows, doors or fans. It is also helpful to discuss skin-to-skin contact for warmth after delivery, with the parents (RCM 2008, RCM 2010).
It is good practice to record the temperature of the birthing room in maternal and neonatal notes (WHO 1997).
The midwife should prepare warmed soft towels, blankets and baby clothing (including a hat) by using the radiant heater of the resuscitaire, radiator, or warming pad. If there is a clean microwave oven available, this can be used to warm clothes quickly. Blankets should be warm but not hot enough to cause any trauma to the neonate.
Prior to the birth, the cleaned resuscitaire is prepared – putting the radiant heater on pre-warmed mode, and heating sheets and blankets. Portable/transport incubators must always be fully charged and heated, with additional warmed blankets, ready to go at short notice.
Initial newborn care
A knowledge of physiology increases understanding of the implications of the neonate being exposed to heat or cold stress and directs care needs.
The neonate’s head (the largest surface area) should be dried by the midwife or possibly birth partner, as it enters the cooler birthing environment. A full-term baby’s temperature may drop by 1–2°C within 30 minutes of birth if heat loss is not prevented (Fanaroff & Martin 2001).
As the neonate is born, he may, according to maternal wishes, be placed on the mother’s abdomen – a source of heat and comfort to the newborn baby, and an effective method of preventing heat loss whatever gestation. The midwife dries the baby, discards the damp towel, then covers the baby with a fresh warm towel. A hat may be applied, while parents provide skin-to-skin contact to reduce heat loss (RCM 2008, RCM 2010, McCall et al 2008) (see website).
When using skin-to-skin contact, the baby can be placed upright, prone on the mother’s (or father’s) bare chest between the breasts, head turned to the side, wearing a nappy, a hat, and covered with a warm towel. Observations are maintained to ensure that the airway is clear, and both mother and baby are comfortable (Karlsson 1996, McCall 2008). Skin-to-skin contact can maintain warmth if the baby was born by lower caesarean section under epidural, enabling the baby to stablilize its heart and respiratory rate, and maintain temperature, more effectively than if the baby remained in a cot or under radiant heat.
Babies of less than 31 weeks’ gestation will have inadequate keratinization of the skin, enabling evaporation of water and heat through the skin (Avery et al 1994). Some units place the baby up to the neck in a special plastic bag after being dried. This can be useful in preventing heat and fluid loss in babies born with a congenital abnormality, such as exomphalos (see Ch. 36). It is important to note that plastic bags are only used if the baby is nursed under a radiant heater.
Care given in the first hour of life is important to the physiological wellbeing of the newborn baby and equally important is the care he receives to remove fear, discomfort and pain from the environment in which he now finds himself. Supporting the woman to breastfeed her baby within the first hour of birth can provide the same human contact that the baby has known for the previous 40 weeks of gestation and enables the development of maternal–infant interaction (Lamb 1983, Moore et al 2007 ), as well as providing a high level of nutrients to the baby to maintain brown fat metabolism (see website).
Bathing
The timing of the first bath has depended on the hospital culture and its carers as well as the wishes of the parents. Bathing babies soon after birth should be avoided. Babies are cleaned by drying with a warm towel and bathed at least 24 hours to 5 days later, to maintain temperature and also to minimise harm to the newborn skin.
Awareness of blood as a potential risk for hepatitis B virus and human immunodeficiency virus (HIV) transmission (Hudson 1992) has led to many hospitals encouraging staff to routinely bathe babies soon after birth to reduce exposure to blood-borne pathogens for healthcare workers and family members (Varda & Behnke 2000).
Midwives owe a duty of care to the newborn and should work towards individualized care to mother and baby. Care should be driven by the needs of the neonate and the mother, avoiding routine practice and ‘care by the clock’. Bathing should not be undertaken unless the baby’s temperature and wellbeing are stable (Bergström et al 2005). Premature babies may be unable to tolerate the additional oxygen and glucose demands of maintaining a temperature above 36.5°C and may become cold-stressed.
Prior to a bath, the midwife needs to consider factors including the reason for bathing and the current condition of the baby, and factors that may impact on the baby’s individual response (Varda & Behnke 2000):
Where
Bathing the baby prior to transfer to the postnatal ward exposes the baby to a greater risk of hypothermia, as differences in air temperature from one area to another may be greater than a newly bathed baby can tolerate. If mother and baby remain in the same room (as in a home birth or birth centre), this is less likely.
When
Nutrition takes priority over cleanliness. The mother should be supported to breastfeed as this will facilitate successful breastfeeding. Baseline observations need to be within normal criteria (see Ch. 41). Prior to bathing, the temperature should be 36.7°C or above. The baby’s temperature should be monitored and recorded in the first few hours of life (Varda & Behnke 2000).
How
The ambient temperature needs to be between 25°C and 28°C, to minimize evaporative, conductive, convective and radiant heat loss. The water temperature should be 36.7°C and a radiant heater should be available to increase the environmental air temperature. After the bath, the baby should be dressed appropriately and given to parents or placed in a warmed cot.
Resuscitation
Home environment
The area prepared for resuscitation must be warm. A changing mat can be used with a nest of warmed towels in which the baby is placed after being dried and the wet towel discarded. This can be achieved by the use of heat pads.
Resuscitaires have an overhead radiant heater which can work from three different settings:
Thermoregulation is a life-or-death issue to the premature infant and it has been recommended that ‘all labour ward and paediatric staff should be trained in the thermal care of the infants at resuscitation’ (CESDI 2003).
The moment the baby is placed on the resuscitaire and under the radiant heater, the midwife needs to put the setting to either manual or servocontrol. When servocontrolled baby mode is used, the temperature is set to 36.8°C. A small area on the left side of the baby’s abdomen is cleaned of vernix using a Mediswab, the silver side of the probe placed on the abdomen, and secured with a reflective disc. This protects the probe from the infrared heat source, ensuring that it does not overheat. Overheating may result in inaccurate information going to the computerized sensor, causing the baby to become hypothermic as the radiant heat source output is reduced. The probe must be monitored regularly to ensure that it remains attached properly and keeps the baby’s temperature stable.
The baby should be positioned to ensure the whole of the body is under the heat – the baby may move down the table away from the radiant heater during resuscitation. It is also important not to occlude the radiant heat source.
Poor radiant heater use can lead to hyperthermia and dehydration, or hypothermia, which causes respiratory and metabolic acidosis, increasing the risk of morbidity and mortality.
Warm gel pads can be used to provide conductive heat gain and support thermoregulation when transferring the newborn from the labour ward to the neonatal intensive care unit (NICU).
Oxygen therapy
Oxygen is cold and it is important when administered facially, that a flow of 1–2 litres only is used with the mask firmly over the baby’s face, avoiding the whole face/head becoming cold. In some units, resuscitaires have humidifiers attached to them which replace fluid lost and also provide warmed oxygen.
The temperature should be recorded at 30 minutes of age in order to take appropriate action if heat is being lost rapidly (CESDI 2003).
Examination of the newborn
Once the baby is given to the parents, they will often wish to uncover and examine him carefully from head to toe. As long as the room is maintained at 25–28°C and the baby is dry, the parents can be left to get to know their newborn baby (UKSC 2008).
The midwife usually performs an examination of the neonate soon after birth and this requires a warm and draught-free environment as the baby is usually exposed (Fanaroff & Martin 2001). The more in-depth examination requires a safe surface area and will be undertaken with the baby naked, therefore it needs to be carried out under a radiant heater and on a firm mattress at the correct height (see Ch. 41).
A superficial examination can be performed whilst the baby is in his mother’s or father’s arms. This keeps the baby warm through the warmth of the parent’s skin and provides an opportunity for the midwife to educate the parents about what is being looked for and why. This is a time for parents to wonder at the miracle that is their baby and for the midwife to assist in this and not to rush or bustle or make it seem an everyday episode.
Temperature
Within a short time, the baby’s temperature begins to adjust to the extrauterine environment. If the maternal temperature is 37.8°C immediately following the birth, the neonate could be expected to reflect that and a temperature of 38.8°C may be acceptable.
Using the rectal route for routine temperature measurement is no longer a justifiable procedure. Historically, this was carried out to confirm the patency of the anus (now examined visually by observing whether the anus is midline and patent – see Ch. 41).
Temperature is normally measured via the axilla. If the baby becomes cold, BAT begins to metabolize, which may give rise to a normal temperature reading, and/or the area of BAT concentration being warm. The baby must be assessed carefully, and rectal temperature assessment might be required.
Transfer
On transfer from one environment to another, there is an increased risk of temperature loss in transit. Transferring the baby from the labour ward to the postnatal ward is best done by placing the baby next to the mother, covered loosely. If transported in the cot, the baby needs to be dressed appropriately, including a hat. If the woman has not brought clothes for the baby, the neonatal unit always has clothing which can be utilized.
The best method to transport sick and premature babies to the neonatal unit is to place the baby in a stable environment, such as the transport incubator, facilitating warmth, observation and care.
If accompanying a woman with an in-utero transfer, the midwife must be prepared for the birth and should have towels and space blankets available to minimize heat loss while in transit.
The ideal and safe environment to transfer a baby from home to hospital is by using the portable incubator to maintain a stable warm environment. If, however, one is not available the ambulance must be sufficiently warm to allow observation of colour and respiratory effort. If the baby has no breathing problems, skin-to-skin contact can be used to support thermoregulation.
The midwife should record the temperature before and after leaving one area for another, whether in the hospital or community. Cots must be placed away from draughts and large expanses of window.
Monitoring and maintaining temperature
Monitoring
Mercury devices are gradually being replaced by infrared electronic probes or electronic probes and occasionally tympanic thermometers. Electronic and infrared thermometers predict the temperature within 60 seconds (Leick-Rude & Bloom 1998, De Curtis et al 2008). Servocontrol is used to reduce handling and maintain an automatic response to temperature changes in the baby.
The rectal temperature is one of the most accurate measurements. The rectum bends sharply to the right and the passing of the hard thermometer may potentially cause a perforation. The probe must be well lubricated with Vaseline or soft paraffin prior to insertion, and inserted no more than 3 cm into the rectum of the term baby and no more than 2 cm in the preterm (Blackburn 2007, Fleming et al 1983). Stool in the rectum can influence the accuracy of readings.
Core temperature drops only when the baby’s effort to produce heat has failed. A rectal temperature in the normal range does not therefore mean no cold stress; it may mean that the baby has activated brown fat metabolism and is producing chemical heat to maintain its temperature. This is achieved as the hypothalamus recognizes a temperature of less than 36.0°C and switches on the ‘central heating’ in the form of non-shivering thermogenesis. The cause of the hypothermia needs to be isolated and removed prior to the baby utilizing brown fat stores and becoming cold-stressed and sick.
Temperature is now measured in the axilla, which contains a large area of brown fat tissue which, when non-shivering thermogenesis takes place, releases chemical energy, causing the area to become warmer than core temperature. Therefore, the reading will be higher than the core in a hypothermic baby (Bliss-Holtz 1991), up to 0.49°C from the core temperature providing a false positive result, making it difficult to recognize hypothermia. Following positioning of the probe (see Fig. 42.1), the arm is brought down and held firmly against the body, which encloses the probe to avoid inaccurate results being recorded. Midwives must assess the temperature of the individual baby through behavioural and physiological signs and symptoms of cold stress. If the routine practice is to take axillary temperature, it does not preclude the midwife taking a rectal reading if the baby is assessed to be in danger of being hypothermic.
Tactile reading/human touch can validate the reading given by the axillary site. Comparing the abdominal temperature, which is representative of the core temperature, with the extremities, can identify a cold baby. Warm, pink feet and abdomen indicate that the baby is in thermal comfort. Cold feet and warm trunk indicates that the baby is in cold stress. In hypothermia the feet and trunk are cold to touch (WHO 1997). If the feet are red and hot, face flushed and the baby restless, the baby could be overheated.
The use of the inguinal site may be useful as there is a good blood flow and no brown adipose tissue to confuse readings, but research has yet to validate it as an accurate means of monitoring temperature in the newborn.
Tympanic temperature appears to be an excellent and accurate way to take the temperature of children and adults but is less accurate for newborn babies. To obtain an accurate reading, the infrared probe must be small enough to be inserted deeply into the meatus to allow orientation of the sensor against the tympanic membrane. This may be achieved if the pinna is supported to straighten the ear canal (Craig et al 2002).
The majority of babies maintain their temperature well but there are times when parents become concerned about their baby and need to be taught a safe method to assess their baby’s temperature in order to detect hypothermia or hyperthermia early. This can be done by using a thermometer or by feeling the baby’s skin (touch assessment) and observing other signs.
Another non-invasive method for taking the temperature of the baby is the Thermospot – a 12-mm sticky black disc that changes to a ‘smiley’ face when the reading is complete. Parents are asked to place this high in the axilla or over the liver area in the epigastrium. This is not reliable if the temperature of the baby is below 35.5°C (Morley & Blumenthal 2000).
Maintaining temperature
The mother is a great source of heat for the baby when the baby is held in her arms. The midwife should encourage the mother to hold her baby close to her body to promote warmth and also engender a greater sense of intimacy. This method of maintaining temperature was investigated in a study at the Hammersmith Hospital in 1987, earning the term kangaroo care, also known as skin-to-skin care, and often used for very small neonates (Whitelaw et al 1988). A similar approach to care was used in a study in Colombia, in which very preterm and small-for-gestational-age babies were nursed inside their mothers’ clothing between their breasts (Sleath 1985). There was a 95% survival rate for babies of 500–2000 g; improved rate of breastfeeding and closer maternal–baby interaction. Similar good outcomes have been found using the same approach in London.
Babies requiring surgery have particular needs which must be assessed according to the reason for and type of surgery (see website).
Minimizing the risks of hypothermia
Wrapping and swaddling
Warm towels or blankets and clothing for the baby are essential; however, tight swaddling which restricts movement may have a detrimental effect on thermoregulation and respiration during sleep and is discouraged, especially for a baby left in a cot.
When placing the very premature baby under the radiant heater, the baby is usually placed into the plastic bag wet, as this minimizes water and heat loss through evaporation (Laptook & Watkinson 2008).
Hats and clothes
The use of hats for the newborn, especially for those that are small for gestational age and preterm, and babies who are being resuscitated, has proven effective in reducing heat loss from the largest surface area of the baby.
The midwife should ensure that babies’ clothing is of natural fabrics and not too close-fitting. It is better to use several layers of thin clothing rather than one or two thick layers. The midwife needs also to ensure that there are no loose threads which may become wrapped around the neonate’s fingers or toes, as these can cause considerable trauma if not discovered quickly.
Bathing
Bathing the baby cleanses and provides an opportunity to assess and validate the baby’s wellbeing by observing physiological behavioural patterns, and is an excellent time for baby and family to interact (Karl 1999). This may be viewed by some midwives as a time-consuming or mundane task, better delegated to a healthcare support worker. If midwives delegate this, they must ensure that the person providing care is able to assess the wellbeing of the baby prior to the bath, provide information and advice at an appropriate level to the parents and provide a report back on the baby’s wellbeing. Throughout the bath, wellbeing should be assessed following the cues the baby is providing and these should be pointed out to the mother (see Ch. 41).
Parent education
Educating parents in the care of their babies at home includes giving advice on suitable clothing for the baby in terms of material and the number of layers required to maintain both heat and ventilation. A checklist can be useful for educating parents of small babies going home, which includes practical advice on helping babies keep warm indoors and outdoors (see website for information leaflet). This information should be translated into appropriate language for those whose first language is not English, particularly for those who have little knowledge of newborn care in the UK climate.
Social workers can be mobilized in circumstances where financial help is needed to assist with heating bills and adequate home insulation or ventilation.
The sick neonate
Hypothermia
Hypothermia is a temperature less than 36.5°C. The baby is more at risk of becoming hypothermic during the first 12 hours following birth, though it can occur at other times during the neonatal period.
Signs and symptoms of cold stress initially:
As the body temperature continues to decrease, the baby features:
If not addressed at this point, the baby will develop sclerema, which is hardening of the skin, and the face and extremities become red, giving a superficial impression of healthy rosiness.
As the baby utilizes oxygen to metabolize brown fat, it reaches its limit, and as there may already be hypoxia, this leads to impaired cardiac function and haemorrhage (especially pulmonary). Cellular function switches from aerobic to anaerobic metabolism, leading to the production of lactic acid and metabolic acidosis (Fig. 42.2). Hypoglycaemia can also cause acidosis, and as the brain does not tolerate lack of glucose, neurological damage can occur. If severe cold stress is not treated, the baby develops kernicterus and clotting disorders and dies (Blackburn 2007, Rennie 2005).
Figure 42.2 Physiological consequences of cold stress. BAT, brown adipose tissue.
(From Blackburn 2007:718.)
Management
There is no general agreement on the management of hypothermia but prevention is the best treatment. Rewarming the mildly hypothermic neonate is not problematic but debate continues about the virtues of rapid versus slow rewarming and their respective advantages and disadvantages in severe cold stress. Slow rewarming is the usual practice.
Moderate hypothermia (temperature 32–35.9°C)
The baby is placed clothed, but not covered, under a radiant heater or in an incubator set at a temperature of 35–36°C. Alternatively, the baby can be warmed using a gel- or water-filled mattress set at 36.5°C, with the room temperature set at 32–34°C.
In the home environment, if clinically stable, skin-to-skin contact with the mother in a room with a temperature of at least 25°C can be used.
Severe cold stress
The main aim is to maintain a thermal environment in which the baby is not required to increase his/her basal metabolic rate. The baby is rewarmed slowly to avoid hypotension due to vasodilatation of the peripheral circulation and acidosis. Rapid rewarming may induce apnoea and cardiac failure. Because oxygen consumption is minimal with gradients of less than 1.5°C, incubator temperature is set at 1.5°C higher than the baby’s core temperature and adjusted every 15–30 minutes. The baby must be naked to allow the heat from the incubator or radiant warmer to warm him. The baby should preferably not be fed gastrically, as hypothermia reduces evacuation of gastric contents and reduces peristalsis. Intravenous fluids ensure adequate fluid and glucose intake but it is important to warm all fluids given to the baby prior to administration.
Hyperthermia
Hyperthermia is a temperature of more than 37.8°C. This is less common in newborn care. Pyrexia may be due to excessive environmental temperatures; incubator overheating (or the greenhouse effect of an incubator in the sunlight); overdressing the baby; infection; dehydration; or a change in central control by drugs or cerebral damage.
As with cold stress, hyperthermia results in increased metabolism and oxygen consumption. It is important that the baby is cooled slowly. This means removing woollens or leaving the baby with only one blanket. Extreme measures, including leaving the baby in thin clothes or restricted bedding, must be avoided.
Reversal of heat stress
The aim in reversing hyperthermia is to reduce metabolic heat production. The baby will attempt to assume an extended position, allowing heat loss via the external gradient to the environment, and to aid this process the baby should have most of his clothes removed. Damp-sponging babies is not recommended. This encourages rapid heat loss, which may then lead to cold stress and shock (Kenner et al 1993).
Once the cause of the hyperthermia has been corrected, the temperature should return to normal within 1 hour. If improvement is not noted within that hour and the baby remains pyrexial and looks unwell, infection must be excluded and brain damage needs to be investigated (Rennie 2005).
Effects and signs of hyperthermia
Hyperthermia increases the metabolic rate and the evaporative water loss rate, which can cause dehydration. The baby is unable to fully utilize the mechanism of sweating to reduce heat. The exception is the baby born to a mother with substance abuse, when the baby may become sweaty and wet when stressed and hyperactive. In the normal term baby, the only area of the body on which sweating takes place is the head, and, in times of shock, the palm of the hands.
Signs of hyperthermia are not easily apparent, and include restlessness and crying. As a result of metabolic rate increases, there may be tachypnoea and tachycardia. The baby’s face and extremities are red because of vasodilatation. This is a serious sign of hyperthermia and must be acted upon to reverse heat gain by isolating the cause. If this does not occur and the temperature rises above 42°C, the baby will go into shock; convulsions and coma may occur.
As with hypothermia, the main cause of hyperthermic stress in the newborn is due to misinterpreting the environmental temperature and its effect on the baby. This can happen by leaving the baby in a closed car on a hot and sunny day; overdressing the baby on a cold day whilst inside; or putting the baby too close to a heat source.
Equipment
Equipment must be used appropriately and with consideration of the thermoregulatory effect.
Incubators
These should be used only for those babies who are ill, likely to become ill, or less than the 9th centile. Modern incubators now have double walls to stop radiant heat loss. The air temperature can be controlled manually or automatically. Incubators and radiant warmers also have an automatic servocontrol skin probe attachment.
The transport incubator
This is more familiar to the neonatal nurse than to the midwife, and provides the means of transferring, monitoring and supporting the small or sick neonate. The midwife should, however, gain a basic understanding of this equipment and its use (see website).
Heated mattress
Two types of mattress are used:
Phototherapy
This can be delivered to the baby in an incubator, cot or open bassinet with a servocontrolled overhead radiant heating source. The neonate’s temperature must be monitored via the axilla, and recorded 3–4 hourly, as the baby can become hyper- or hypothermic during this treatment.
Conclusion
Although a homeotherm in the true sense of the word, the neonate has higher heat and water losses than those of the adult, so a thermal environment that allows a minimal resting metabolic rate must be provided. Midwives should give special attention to the maintenance of a ‘normal’ temperature, particularly in the ‘at-risk’ neonate. An understanding of the physiology of temperature control, calorific intake and application to practice is vital so as to provide a safe transition to extrauterine life.
The midwife is a key practitioner in preparing, supporting and educating the mother and her family in thermoregulation, its impact on the baby, and deviations from normal.