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MARY A. SHORT, RN, MSN • Section Editor
Keeping Infants Warm
Challenges of Hypothermia
Martha J. Mance, MS, RN, NNP, CPNP
ABSTRACT
Hypothermia is a major cause of morbidity and mortality in infants; therefore, maintaining normal body temperatures
in the delivery room is crucial. An understanding of how infants produce heat and what can be done to maintain normal
body temperatures in full-term and preterm infants is essential for the preservation of thermal stability in this population.
This article reviews the consequences of hypothermia, mechanisms of heat exchange and heat production in full-term and
low birth-weight infants, and discusses interventions in the delivery room to alleviate hypothermia.
KEY WORDS: hypothermia, temperature regulation, neonate, delivery room
ypothermia is a major cause of morbidity
and mortality in infants, underscoring the
importance of maintaining normal body temperature in the delivery room. The World Health
Organization (WHO) lists hypothermia as a “top killer”
during the neonatal period1 and suggests that it is
widely underreported and underestimated as a cause
of death.2 Cold stress is associated with lethargy, hypotonia, poor feeding, weight loss, abdominal distention,
vomiting, restlessness, pallor, cool skin, tachypnea,
respiratory distress, and a significantly reduced core
temperature.3 Hypothermia has been related to hypoglycemia, hypoxia, metabolic acidosis, coagulation
defects, and severe intraventricular hemorrhage.4
Reductions in body temperature may delay transition
from fetal to neonatal circulation at birth secondary
to the effect of temperature on pulmonary vasomotor
tone and acid-base homeostasis.5 Pulmonary hemorrhage may result from acidosis secondary to shock and
hypoxia, causing left ventricular failure and increased
pulmonary capillary pressure.3 Cold stress may have
an important role in stimulating the onset of breathing6
and protecting the brain following a hypoxic, ischemic
event but can have disastrous consequences if not
stopped,7-10 making early intervention in the delivery
suites imperative. This article reviews the consequences
H
Address correspondence to Martha J. Mance, MS, RN, CPNP,
Nurse Practitioner, Neonatal Intensive Care Unit, Women
and Infants’ Hospital, 101 Dudley Street, Providence, RI
02903; reignamjm@aol.com.
Author Affiliation: Women and Infants’ Hospital, Providence,
Rhode Island.
Copyright 2008 © by the National Association of Neonatal
Nurses.
6
of hypothermia and mechanisms of heat exchange
and heat production in full-term and low birth-weight
infants and discusses routine interventions that can
be implemented in the delivery room to minimize
hypothermia.
A CONTINUING PROBLEM
A number of studies have reported the problem of cold
stress in neonates. The EPIcure study, a large prospective observational study in the United Kingdom and
the Republic of Ireland, evaluated outcomes of infants
between 20 and 25 weeks’ gestation (n = 843). The purpose of the study was to describe survival and health
problems in this population of infants at the minimal levels of viability. The results demonstrated that
40% of the infants were hypothermic (temperatures
< 35°C; P < .001). These infants were in more critical condition than were those with normal temperatures upon admission to the NICU.11 A second study
reported that 29% of infants less than 30 weeks’ gestation born by cesarean section were admitted to the
neonatal intensive care unit (NICU) with axillary temperatures lower than 35.6°C.12 Another research team13
found that more than one-quarter of the infants were
hypothermic, despite implementation of the Neonatal
Resuscitation Program14 (NRP) guidelines to prevent
cold stress. Cold stress in the delivery room contributes
to increased oxygen consumption and potentially interferes with an effective resuscitation.15 Others have
described low admission temperatures in 15 centers
of the National Institute of Child Health and Human
Development Neonatal Research Network,16 and hospitals in developing countries1 continue to document
the problem of hypothermia on admission. These
studies11,16,17 reveal reduced survival rates in infants
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TABLE 1. Normative Values
Neutral Thermal
Environment
An Environment in Which Body
Temperature is Maintained with the
Lowest Expenditure of Energy and
Oxygen Consumptiona
Normothermia
36.5°C-37.5°Cb
Hypothermia
< 36.5°Cb
Hyperthermia
> 37.5°Cb
a
From Vohra et al.21
From World Health Organization (WHO).1
b
admitted to facilities with temperatures less than
36°C. Although the consequences of hypothermia are
severe, difficulty exists in delineating what is normal
body temperature for infants.1,3,4,17-23 Table 1 outlines
normative values for a neutral thermal environment,
normothermia, hypothermia, and hyperthermia.
HEAT LOSS
Cold stress is a condition in which heat loss is greater
than heat production, resulting in the inability to maintain core temperature. Maintenance of body temperature is dependent on an intact central nervous
system, the ability to produce heat, the availability
of oxygen, and an energy source. Infants exchange
heat with the environment through evaporation, con-
duction, convection, and radiation. Table 2 discusses
the mechanisms of heat loss and interventions that
can be implemented at delivery to minimize heat loss
that occurs from each mechanism.
Low birth-weight infants are less able to prevent
heat loss or to produce heat than healthy full-term
infants, making them more susceptible to cold stress,
particularly at birth. Risk factors identified that increase
the risk of hypothermia include prematurity (gestational age [GA] < 37 weeks), low birth-weight,24,25
intrauterine growth restriction, small-for-gestationalage (SGA) infants,26 low ambient or environmental
temperature, asphyxia,24 impaired central nervous
system function,16 and maternal temperature.25 Open
defects in the skin, including omphalocele, gastroschisis, and neural tube defects, also place the infant at an
increased risk of heat loss.
Very premature infants and infants with a birth
weight of less than 1000 g have high evaporative heat
losses and immature thermoregulatory mechanisms
with reduced vasomotor response to cold stress during
the first days after birth.27 The primary goal when caring for extremely low birth-weight (ELBW) infants
is to provide a neutral thermal environment in which
heat loss can be prevented28 and oxygen consumption
is maintained at resting levels.15 Extremely low birthweight29 and SGA26 infants are already predisposed
to cold stress because of their physical characteristics.
These infants have insufficient subcutaneous fat necessary for insulation, reduced amounts of brown adipose
tissue (BAT), a limited ability to mobilize norepinephrine and fat for energy production, and a diminished
capacity to increase their oxygen consumption. In
TABLE 2. Mechanisms of Heat Loss in the Infant33
Mechanism
Definition
Intervention
Evaporation
Heat loss occurs as moisture on the body surface or from the
respiratory tract vaporizes. The loss depends on air speed and
relative humidity.
•
•
•
•
•
Dry well
Add humidity to the environment
Humidify oxygen
Use polyethylene wraps
Decrease air currents around the infant
Conduction
Transfer of heat from one surface to another by contact.
Determined by a temperature gradient as heat moves from an
area of higher temperature to lower.
•
•
•
•
Prewarm radiant warmers
Cover scale with warm blanket
Have many warm blankets available
Use portable warming mattress
Convection
Heat is dissipated from the interior of the body to the skin surface through the blood. It is conducted from the body surface to
the surrounding air and will be displaced from the skin and carried away by diffusion to moving air particles at the skin surface.
•
•
•
•
Place hat on a well-dried head
Swaddle infant
Avoid drafts
Use warmed gas for resuscitation
Radiation
Transfer of radiant energy from one body surface to surrounding cooler or warmer surfaces. Heat loss is independent of
ambient temperature, air speed, or other heat loss mechanisms.
• Prewarm the radiant warmer and the
transport bed
• Keep warmers away from external walls,
windows and direct sunlight
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addition, they have large surface-area-to-mass ratios
and an extended posture that further increases the
surface area from which they may lose heat. A higher
total body water content and thin, immature skin without a well-defined stratum corneum exposes them
to increased transepidermal water loss (TEWL) and
increased heat loss.28,30 Decreased glycogen stores31
and poor vasomotor control further increase the risk
for hypothermia in ELBW infants.27,30
Reduction of TEWL can be achieved by maintaining elevated levels of humidity in the environment. Increasing the humidity in the premature
infant’s environment improves temperature control
and fluid balance in infants.31,32 Radiant warmers
are competent at supplying an adequate heat source
for premature infants but increase the amounts of
insensible water loss. The infant is left exposed to air
movement around the warmer, increasing convective
heat loss.23 Placing plastic wrap over, but not touching, the infant’s skin and adding water vapor under
this covering will help to reduce evaporative and conductive losses.30 Transferring the infant to an isolette
with added humidity will also reduce loss of heat from
evaporation.
HEAT PRODUCTION
Body temperature is maintained by controlling the
balance between heat production and heat loss. The
3 mechanisms by which infants can produce heat to
alleviate cold stress are:
• Vasoconstriction
• Brown fat lipolysis
• Alterations of body position
In response to cold, the sympathetic nervous system
stimulates the peripheral vasculature, resulting in vasoconstriction, reducing skin blood flow and heat loss
through conduction. It also induces brown fat lipolysis, resulting in heat production by nonshivering
thermogenesis.33 Healthy, full-term infants are able to
shiver, but at birth they are able to generate more heat
via nonshivering thermogenesis (metabolism of brown
fat). Premature infants have a diminished capacity
to shiver as well as limited stores of BAT.23 The final
method for heat conservation is alteration in body
position by flexion of the extremities in an effort to
conserve heat (decreasing the exposed surface area)
or by increasing motor activity.34
Thermal receptors in the skin and core send information to the hypothalamus, which detects deviations
in temperature from a set point and mediates a
response through the autonomic, somatic, and
endocrine systems.3 Infants respond to cold stress by
increasing their oxygen consumption,15 which initially
results in oxidative metabolism of glucose, fat, and
protein to produce heat. Nonshivering thermogenesis
is the primary mode of this heat production in the
infant. Brown adipose tissue first appears in the infant
around 26 to 30 weeks’ gestation and continues to
develop for several weeks postnatally. It is found in the
mediastinum, around the great vessels, and around
the kidneys, and adrenalglands. Stores are also found
in the axilla, the nape of the neck, and between the
shoulder blades. It has numerous fat vacuoles and
mitochondria with large stores of glycogen and an
extensive blood and nerve supply.33 A drop in skin
temperature results in the initiation of nonshivering
thermogenesis (metabolism of BAT) by hormonal
mediators and the sympathetic nervous system. The
BAT breaks down into glycerol and nonesterified fatty
acids, which release heat. Brown adipose tissue is
dependent on oxygen for the lipolysis of this fat during this production of heat. Hypoxia disrupts thermoregulation by causing a redistribution of circulation and ineffective capillary blood supply in BAT.35,36
Prolonged cold stress reduces energy stores and leads
to a cascade of events as hypoglycemia aggravates
metabolic acidosis, which delays fetal transition.5
Although infants are able to increase their metabolic rate in response to the low environmental temperatures found in delivery rooms, all infants have an
initial drop in body temperature.33 The temperature
gradient between the infant’s skin and the environment
is the critical factor that elicits an increase in oxygen
consumption and metabolic rate, potentially resulting in an accumulation of aerobic waste products.15
If the cold stress is not removed or the infant becomes
hypoxic, the oxygen demand becomes greater than
supply, and an accumulation of anaerobic waste products occurs, which compounds the resulting metabolic acidosis. The colder the infant, the more severe
the hypoxia and acidosis become.5
ACHIEVING NORMAL
BODY TEMPERATURES
Heat is transferred along a gradient from areas of
higher temperatures to lower temperatures. Infants
are delivered from a warm, shielded uterine environment into a cold, dry delivery room, the perfect
setting for heat loss. This is why it is essential for
providers to implement interventions to prevent
hypothermia.20 Because of the potential detrimental
consequences of hypothermia, interventions such as
routine care and polyethylene wraps have been
studied to determine if they help to reduce or prevent the drop in temperature so frequently noted in
infants.
Routine Care in the Delivery Room
Ambient temperature has a significant influence on
heart rate (HR), HR variability, respiratory rate,
oxygen consumption, and insensible water loss in
ELBW.28 Body temperature and oxygen consumption are inversely related; as body temperature falls,
the fraction of inspired oxygen required for survival
increases.28 The WHO advocates maintaining the
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temperature in the delivery room at 25°C.1 It is
known that the environmental temperature of the
delivery room has a direct impact on heat loss in all
infants; maintaining delivery room temperature is a
simple intervention to implement.36 Drying and then
placing a newly delivered infant under a radiant
warmer has been shown to limit the fall in body
temperature.37 Even with this simple intervention, a
fall in body temperature occurs. By modulating the
environmental temperature to reduce the gradient
between skin and air, the infant’s metabolic rate can
be maintained, energy stores conserved, and acidosis prevented.15
Routine thermal care includes maintaining the
delivery room at a minimum of 25°C,1 placing the
infant under a radiant warmer, and immediately drying the infant, paying careful attention to drying the
head. Wet linens should be removed quickly, and the
head should be covered with a hat. The infant should
be wrapped in prewarmed blankets, and any other
contact surfaces such as a scale, should be prewarmed.
Drafts should be avoided.22 The competency checklist
outlines procedures for routine care in the delivery
room (Table 3).
Employing Polyethylene Wraps
Several studies have demonstrated the success of
utilizing polyethylene occlusive wraps to keep LBW
infants warm at the time of delivery.17,21,24,25,38 Following
delivery, providers place the wet infant into a polyurethane bag on the warmer, keeping the infant’s head
exposed (Figure 1). The head and face are then dried,
and resuscitation continues following NRP guidelines.14 The clear plastic wrap permits visualization of
the infant39 and any interventions needed are performed with the infant in the bag. For more extensive
resuscitation requiring umbilical or peripheral lines,
healthcare providers cut holes in the bag to gain
access.17 The infant is then placed on warmed blankets and transferred to the NICU, where the infant is
placed on a radiant warmer and the polyethylene bag
is removed.25 Polyethylene bags permit heat to be
gained by the infant through radiation and reduce the
amount of evaporative heat loss.32,39
TABLE 3. Competency Checklist for Maintaining Infant’s Temperature in the Delivery Room
Healthy Full-term Infant
1. Radiant warmer in delivery room should be set up
ahead of time per hospital routine with warm blankets
over the mattress.
2. Have radiant warmer set to 25% maximum power at
all times. Prior to delivery, the warmer should be on
manual mode and reset to maximal power.
10. Have a clean, warmed blanket available to wrap the
infant prior to presentation to the parents.
11. Maintain an environment that promotes a neutral thermal environment, avoiding drafts and keeping the room
warm.
a. Additional blankets can be brought in from blanket
warmer just before the birth.
12. Skin-to-skin care can be initiated once infant and
mother have been dried and a hat has been placed on
the infant’s head. (This can be accomplished on the
motherís abdomen.) Once skin-to-skin care is initiated,
a warm blanket should be placed over the infant,
cocooning the infant with the mother.
b. Have a warmed, dry blanket ready to receive the
infant upon birth.
Preterm Infant
1. Follow steps 1–3 for the healthy full-term infant.
3. Place drying towels directly under the warmer and
over the drying blanket.
4. Once the infant is brought to the warmer, he/she
should be dried quickly with the warmed, dry
blanket.
5. Remove the wet blanket and continue drying with the
towels and blanket on the warmer.
6. Dry the head thoroughly and place a hat on the
infant’s head.
7. The infant can remain on the warmer for further evaluation and resuscitation.
8. Place a temperature probe on the infant’s abdomen,
switch the warmer to servocontrol set at 37.5°C.
9. Place warmed blanket on scale prior to weighing the
infant.
Advances in Neonatal Care • Vol. 8, No. 1
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2. Add a portable warming mattress to the radiant
warmer.
3. Place a polyethylene occlusive wrap on the warmer to
await infant < 29 weeks’ gestation.
4. Once the infant is brought to the warmer, remove the
wet blanket and place wet infant under the wrap or in
the bag and close, leaving the infant’s head out. Place
the infant on the warming mattress.
5. Dry head and place hat on infant.
6. Continue with resuscitation as needed.
7. Any infant being brought to the NICU should be placed
in a warm transport bed and weighed on arrival to the
NICU.
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FIGURE 1.
Transparent Bags to Limit Heat Loss
in the Delivery Room
Transparent bags can be used to limit heat loss in the delivery room.
A retrospective study of infants born at less than
28 weeks’ gestation (n = 77) evaluated the use of
polyethylene wraps to increase NICU admission temperatures. The researchers found that the wrapped
infants’ axillary temperature was greater than that of
infants receiving routine care (P < .001). This study
supports the use of polyethylene wraps to prevent
hypothermia in premature infants less than 28 weeks’
gestation.40 A retrospective preintervention audit of
infants’ admission temperatures found that many
premature infants admitted to the NICU were cold.
Then the investigators performed a prospective postintervention audit following the introduction of polyethylene wraps in infants less than 30 weeks’ gestation
(n = 141). The primary objective was to determine
the effect of admission temperature when the polyethylene wrap was used immediately after delivery
of these infants. The intervention improved admission temperatures in infants less than 27 weeks’ gestation (P < .01).12 A prospective randomized controlled
trial of infants less than 30 weeks’ gestation (n = 88)
evaluated the effect of using polyurethane bags at
delivery in infants less than 29 weeks’ gestation. The
wrapped infants were less likely to have admission
temperatures of less than 36.4°C (P < .01) and had
higher admission temperatures (P < .003).25 In a randomized controlled trial of infants less than 32 weeks’
gestation (n = 62), the effect of polyethylene wrap on
rectal temperature was evaluated. Higher admission temperatures were found in the infants less than
28 weeks’ gestation (P < .001), but there was no difference in admission temperatures in infants between
28 and 31 weeks’ gestation (P = .47), lending support to the use of polyethylene occlusive wraps in
very low birth-weight (VLBW) infants in the delivery room to help preserve core temperature.24 A second randomized controlled study of infants less than
28 weeks’ gestation (n = 55) was undertaken by the
same group to determine whether or not the occlusive wrap used at delivery of VLBW infants would
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prevent heat loss after delivery better than would conventional drying and whether the benefit was sustained once the wrap was removed. The investigators
found higher rectal temperatures on admission in the
wrapped infants (P < .002) but no difference between
groups in rectal temperature at 1 hour of life. This corroborates previous findings demonstrating prevention
in heat loss at delivery of premature infants. The
group also found that the size of the infant had a direct
effect on core temperature, with the smaller infants
having the lower temperatures.21
Because of the VLBW infant’s need for greater thermal protection at birth,21 the primary focus at delivery
is to immediately reduce heat loss. These studies support the recommendation for employing polyethylene wraps at the delivery of VLBW infants to reduce
hypothermia in infants less than 28 weeks’ gestation.
The major limitation of all of these studies is the small
sample size.
IMPLICATIONS
FOR
FUTURE RESEARCH
The use of polyethylene bags has been demonstrated
to work in infants less than 28 weeks’ gestation. Even
though it appears that infants greater than 28 weeks’
gestation do not benefit from this intervention, future
research could be directed to expanding this population to severely SGA infants, using the polyethylene
bags for transportation of premature and full-term
infants born outside of the hospital or sick infants with
poor peripheral perfusion.
Infants lose a significant amount of heat from their
heads, so investigations into head covering with or
without the use of the polyethylene bags would be
helpful. The type of head covering is also an area for
additional research.
IMPLICATIONS
FOR
FUTURE EDUCATION
Hypothermia in the delivery room can interfere
with normal neonatal transition to extrauterine life.
Frequent audits of NICU admission temperatures
are needed to ensure hypothermia is minimized. The
competency checklist describes interventions to prevent cold stress in full-term and premature infants.
The most important thing to remember is to dry the
infant well to the diminish evaporative heat loss that
normally occurs at delivery.
CONCLUSION
Simple and easy interventions can make large differences in the thermal stability of infants. A warm environment in the delivery suite in conjunction with
prompt interventions of routine care, utilizing polyethylene occlusive wraps, and environmental humidity
for LBW infants, can help maintain body temperaAdvances in Neonatal Care • Vol. 8, No. 1
11
ture and protect infants against the detrimental effects
of hypothermia.
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