Thermoregulation for neonates
Temperature
Control or thermoregulation in the neonate is a critical physiological function
that is strongly influenced by physical immaturity, extent of illness and
environmental factors (Thomas 1994). The neonate’s susceptibility to
temperature instability needs to be recognised and understood in order to
appropriately manage and limit the effects of cold or heat stress.
It is
essential that neonates are nursed within their ‘Neutral thermal Environment’
(NTE). This is defined as “the environmental air temperature at which an
infant with a normal body temperature has a minimal metabolic rate and
therefore minimal oxygen consumption” (Merenstein
& Gardiner 1998).
The
maintenance of the NTE, in order to prevent thermal stress is the ultimate aim
of neonatal temperature control and management.
By
definition, the term neonate refers to the first 28 days post-delivery. Due to
the wide range of post-natal ages and gestations seen on NICU, and elsewhere
within the Great Ormond Street Trust, this guideline is appropriate for infants
up to six months of age (post-term). Reference shall be made to specific
gestations, ages and whether intensive care or not, where applicable.
Optimum
thermoregulation and related nursing care can be addressed with regard to three
interrelated areas:
- Method of temperature taking
- Choice of environment
- Temperature instability &
intervention
Monitoring
The acceptable set-point temperature is an axilla temperature of range 36.7 -
37.3°C. This range should be maintained at all times. (Rationale 1)
Tempadot™ (single-use) is the thermometer in use in the Trust (Rationale 2).
A central temperature is obtained by insertion at the axilla site for 3
minutes, placing the dots against the trunk. It must be read 10 seconds
following removal (Rationale 3).
The axilla temperature should be checked 4 - 6 hourly and recorded.If their
temperature falls outside the normal range, readings must be taken more
frequently (every 30-60 minutes). This should be continued until
their temperature has normalised (Rationale 4, Rationale 5).
If a neonate undergoes any change of environment or increased exposure, e.g.
general cares, procedures, phototherapy, new transfer to an incubator or
bassinette, they will require 1-2 hourly temperature checks for the first few
hours until the temperature is stable (Rationale 6).
For neonates receiving intensive care, peripheral skin temperature is monitored
continuously by use of a probe placed on the sole of the foot (Rationale 7,
Rationale 8).
Allow 5 minutes for skin temperature to stabilise once applied to foot
Peripheral temperature is recorded hourly and the probe site should be changed
every 4-6 hours.
If an arterial line is in situ, the foot should be left uncovered (Rationale
9).
The ‘toe-core’ temperature difference is taken from the difference between the
peripheral temperature reading on the monitor and the central readings done at
intervals or continuously (Rationale 10).
Continuous central monitoring can be done by placing a probe over the abdomen
when supine, or the back when prone, preferably over the liver (Rationale 11).
The difference should be between 1-2°C (Lyon et al 1997) (Rationale 12).
Peripheral monitoring can be discontinued when a neonate:
- no longer requires
cardiovascular support to maintain an adequate blood pressure
- is peripherally warm & well
perfused
This will require individual assessment.(Rationale 13).
Environment: Incubator
Any neonate less than 1.5 kg should be nursed within an enclosed incubator
(Rationale 14, Rationale 15).
Any neonate less than 28 - 30 weeks gestation in the first 14 days of life
should be nurses in a closed incubator with added humidity.
The optimum level of humidity is determined by gestational age, days of life,
skin maturity and underlying pathology.
Generally a neonate < 29 weeks, <1kg in weight and in the first 7 - 10
days, should be nursed in 50% humidity or greater (Sedin 1995; Knobel &
Holditch-Davis 2007).
Sterile water should be used and humidity levels checked hourly (Rationale 16)
(Harpin & Rutter 1985).
Neonates at extremes of prematurity may require up to 85 - 95% humidity for up
to 21 days post delivery (Rationale 17).
Before admission pre heat the incubator temperature according to the specific
age & gestation by the use of ‘Neutral Thermal Environment’ (NTE) charts
and adjust incubator temperature according to individual response (Merenstein
& Gardiner 1998; Mok et al 1991) (Rationale 18, Rationale 19).
Check and record incubator temperature hourly.
Alter set temperature according to the neonate’s temperature and adjust by
0.5-1°C every 15 - 30 minutes, depending on the extent of temperature
instability (Rationale 20, Rationale 21).
If a neonate does not require heat inside an incubator, i.e. it is necessary to
switch off the incubator, they should be transferred to an open cot (Rationale
22).
A neonate must not be left in an incubator with its doors open for longer than
one hour (Rationale 23).
Care and interventions, e.g. suction, nappy care, should be carried out via
portholes, avoiding opening the side completely (Rationale 24).
Where appropriate, the incubator should be changed every 7 days, particularly
if humidity is being used (Rationale 25).
This should be recorded.
Environment: Baby Therm
Baby-therms provide heat by a combination of conduction (from below via a gel
mattress) and radiation (from above) (Rationale 26).
Any neonate greater than 1.5 kg and any neonate who necessitates ease of
access, e.g. for lumbar puncture, central line insertion, particularly surgical
& cardiac neonates on admission, is nursed in an open Baby-therm.
If a neonate less than 1.5 kg is admitted into an open heater in the first
instance, they should be transferred into an incubator as soon as possible.
When preparing a Baby-therm for use, the mattress is switched to ‘on’ at a set
temperature of 37°C (Rationale 3).
It will take an hour to heat up to the set temperature.
The overhead heater should be turned on and the ‘Manual’ control should be
selected rather than “Servo” (Rationale 27).
Servo control is not recommended for “shocked” neonates who are peripherally
vasoconstricted:
The heater should be switched to level 5 (each level or bar represents a 10%
increase or decrease in heat from above).
It will take 25 minutes to reach the desired temperature from the overhead
heater.
If the neonate is hypothermic, the initial settings are higher.
This also applies to a neonate already established in a Baby-therm who needs
extra heat.
The extended upper range (indicated as > 37°C; i.e. range 37 - 38.5°C) is
chosen plus level / bar 6 - 10. Above level 6, the heater requires
resetting every 15 minutes (press ‘reset’), which is indicated by an alarm
(Rationale 28).
If the neonate requires cooling, turn the radiant heater off and choose the
extended lower range for the mattress, indicated by <37°C, i.e. 30 - 35°C).
Turn the temperature down by 1°C at 15 - 30 minute intervals (Rationale 29).
Once established in the Baby-therm, there are 4 options to determine what the
neonate is laid on and covered with:
Option One: Both mattress and radiant heater on:
- The neonate should lie directly
onto a sheet covering the gel mattress (Rationale 30)
- Nesting should be provided
around, not under, the neonate (Rationale 31)
- Cover them with bubble wrap,
bubbles downwards, or leave exposed (Rationale 32)
Option Two: Mattress with no radiant heater.
- As option one but the neonate
should be covered with a blanket (Rationale 33).
Option Three: Radiant heater with no mattress.
- Ensure that a padded sheet,
towel or gamgee, is place between the neonate and mattress while it is
turned off. Cover neonate with bubble wrap (Rationale 34).
Option Four: Neither:
- As for option three but wrap
well with blankets (Rationale 35).
When transferring a neonate on a Baby-therm, e.g. to theatre, X-ray or wards,
the transfer should take a maximum of 15 minutes before connecting to mains
supply again (Rationale 36).
Environment: Giraffe Omnibed
This equipment is located and used on NICU only.
The GE Healthcare Giraffe can be used as both a closed incubator with or
without humidity and as an overhead heater when procedures need to be
undertaken which are unable to be performed through the portholes. If opening
the Giraffe it should be noted that the humidity within will cease.
The lid should remained closed other than when procedures are carried out
(Rationale 37) (GE Healthcare 2011).
Environment: Open Cot
A well neonate, >1.5 kg, who no longer requires close monitoring or
intensive care and who can maintain a stable central temperature in 26-28°C
room temperature, can be transferred to a small cot (Medoff-Cooper 1994)
(Rationale 38).
The neonate should be covered or wrapped in blankets and should wear a hat
(Rationale 39).
Weaning a well neonate from an incubator or Baby-therm should be done according
to age and gestation (see NTE chart (Merenstein & Gardiner 1998)), turning
the incubator or mattress temperature down by 0.5 - 1°C each day and observing
central temperature (Medoff-Cooper 1994) (Rationale 40).
Larger infants, i.e. > 4kg, who require warming can be nursed on an open cot
with a bear-hugger blanket, heated mattress and / or single overhead heater.
Interventions: General
Maintain a set environmental room temperature of >26°C.
Specific events may precipitate heat loss the effects of which need to be
counteracted, e.g.: (Sheeran
1996; Roberton 1995) (Rationale
41)
Conduction
- cool x-ray plate
- theatre table
- weighing scales
- stethoscope
They should be prewarmed and covered.
Convection
Avoid over-exposure and maintain a “minimal handling” policy. Use portholes for
all procedures whenever possible and close these as soon as the procedure is
finished.
Radiation:
- cold incubator walls
- direct sunlight
Prewarm incubators, use curtains and covers over the incubator.
Evaporation:
- cold water
- wet skin
- nappy
- bed
Keep skin and bed dry.
Before transferring a neonate to theatre, preparing for procedures or general
transportation:
Pack an appropriate sized bonnet, bubblewrap, dry gamgee or blankets, heat pad
if available and a clean nappy (Rationale 42)
Cover as well as possible (Rationale 43)
During transfers within GOS the neonate should remain in their incubator or
Baby-therm. This should be left switched on, at the same setting, to
await their return from the radiological or surgical procedure (Rationale 44).
Ensure the neonate is transferred to a pre-warmed, dry surface in theatre or
X-ray. (Rationale 45)
The neonate’s temperature must continue to be monitored during transfers &
procedures (Rationale 46).
If their temperature falls outside normal range, recordings must be taken more
frequently, i.e. 30 - 60 minutes, until it has normalised. When it has
returned to the normal range it may be done 4 hourly.
Any intervention carried out for temperature instability must be recorded in
the child’s health care records (Rationale 47).
Interventions: Cold Stress
The signs and associated problems of cold stress are:
- central temperature < 36.5°C
- increase in core-toe gap >
2°C
- mottled and/or pale
- increased capillary refill
time, i.e. > 2 seconds
- increased oxygen requirements
- metabolic acidosis
- tachycardia
- hypoglycaemia
- apnoeas
- bradycardia (Rationale 48)
To intervene in this situation:
- Place a neonate of < 1.5kg
in an incubator at the upper range, i.e. >37°C (Rationale 49)
- If using a baby-therm, set the
temperature at the upper range, both above & below, and follow
guidelines for babytherm use (Rationale 50)
- Increase the set temperature by
1°C every 15 minutes according to the neonate’s response
- Take their temperature every 30
- 60 minutes until warmed to an acceptable temperature
- Identify & eliminate any
environmental causes, e.g. wet bed, over exposure, handling
- Promote a flexed position
- Ensure ventilator gases are
adequately warmed to 37°C
If the cause of decreased peripheral temperature is not due to cold stress,
i.e. central temperature stable but an increase in core - toe gap, the
neonate’s perfusion status should be assessed (Rationale 51).
They should be observed and the following aimed for: (Lyon et al 1997)
- capillary refill time < 2
seconds
- pink colour
- skin warm to touch
- no increase in heart rate above
normal
- palpable peripheral pulses
- blood pressure within normal
range for age, gestation & condition
Interventions: Heat Stress
The signs and associated problems of heat stress are:
- central temperature above
37.3°C and rising
- increased peripheral
temperature and decrease in core-toe gap, i.e. < 1°C
- tachycardia
- tachypnoea
- restlessness
- dehydration
- stress (Rationale 52)
To intervene in this situation:
- Check environmental temperature
and reduce by 1°C at 15 - 30 minutes intervals.
- Remove excess layers and
clothing.
- If under a Baby-Therm, turn
radiant heater off and choose the extended lower range (<35°C).
- Turn the temperature down by 1°
at 15 - 30 minute intervals (Rationale 53)
If the cause is not environmental, i.e. consider NTE <1 - 5°C to maintain
normothermia, consider infection as a cause of the pyrexia. This must be
reported to the child’s doctor and the policy for the management of the pyrexial
neonate followed.
Rationale
Rationale 1:
To allow normal physiological function and body metabolism (Thomas 1994).
Rationale 2: They are safe, quick and non-invasive to use (Leick-Rude &
Bloom 1998; Pontious et al 1994).
Rationale 3: To meet manufacturer’s guidelines
Rationale 4: 4 hourly is the general recommended interval unless instability
occurs.
Rationale 5: The axilla is the safest and most accurate site for central
temperature readings (Leick-Rude & Bloom 1998; Pontious et al 1994; Sheeran
1996).
Rationale 6: It can take up to 2 hours for a central and peripheral temperature
to stabilise following a change to the thermal environment or prolonged
exposure in relation to nursing or medical procedures (Mok et al 1991).
Rationale 7: Peripheral temperature is valuable as one parameter in the
assessment of perfusion.
Rationale 8: The foot is recommended as the most “peripheral” site (Lyon et al
1997).
Rationale 9: to be able to assess the colour and perfusion of the periphery.
Rationale 10: Abdominal/liver skin temperature is closest to the body’s central
temperature and is non-invasive (Drager Ltd 1997).
Rationale 11: Rectal probes due to risk of perforation (Sheeran 1996).
Rationale 12: Less than 1°C may indicate heat stress while greater than 2°C may
indicate cold stress, hypovolaemia or infection (Mitchell 1997).
Rationale 13: The length of time required for optimum perfusion will depend
on:extent of illness,peripheral shutdown,and the nature & timing of surgery
(if applicable).
Rationale 14: They have a greater physiological predisposition to heat loss due
to relatively large surface area to volume ratio.
Rationale 15: An incubator is to provide heat by convection within a closed
environment (Leick-Rude & Bloom 1998).
Rationale 16: The pre-term neonate has high “trans-epidermal” water losses due
to a thin, poorly keratinised skin (stratum corneus). This matures by 21days
post-natal age (Blackburn & Loper 1992). Trans-epidermal water loss is a
major cause of heat loss in the premature neonate (Marshall 1997).
Rationale 17: The more immature, the greater the predisposition to heat loss by
evaporation (Merenstein & Gardiner 1998; Marshall 1997).
Rationale 18: To minimise oxygen and energy consumption and maintain
homeostasis (Sheeran 1996).
Rationale 19: to reduce the risk of heat loss via convection in a cold
incubator.
Rationale 20: To avoid rapid over or under heating.
Rationale 21: To avoid sudden swings in temperature.
Rationale 22: To avoid over heating.
Rationale 23: To avoid sudden changes to their temperature & adverse
cooling.
Rationale 24: To avoid sudden loss of heat from inside the incubator.
Rationale 25: To meet the Infection Control Policy.
Rationale 26: They limit heat loss during exposure & interventions
because of easy access and radiant heater responsiveness (Seguin & Vieth
1996).
Rationale 27: The “Servo” may cause overheating due to the heater responding to
the cool skin temperature (Drager Ltd).
Rationale 28: To avoid the complications associated with cold stress, i.e.
decreased surfactant, increased oxygen consumption, respiratory distress and
hypoxia, metabolic acidosis, hypoglycaemia, weight loss and apnoea (Merenstein
& Gardiner 1998; Roberton 1995)
Rationale 29: To avoid the complications of heat stress associated with increased
fluid losses, hypernatraemia, recurrent apnoeas, convulsions, increased
metabolic rate and tachycardia. (Merenstein & Gardiner 1998; Roberton 1995)
Rationale 30: To achieve optimum heat transfer from the heat pad, via the gel
mattress, to the neonate (by conduction).
Rationale 31: Blankets may block radiative heat transfer from above to the
neonate.
Rationale 32: Bubble wrap provides an insulation layer to prevent heat loss
from convective air currents. The bubbles placed downwards maximise the air trapped
between the sheet & neonate.
Rationale 33: When there is no radiative heat from above, a blanket can be
used.
Rationale 34: To avoid heat loss from the neonate to the cool mattress by
conduction.
Rationale 35: There is no heat source from above or below so the Baby-therm is
being used as a cot alone.
Rationale 36: Once switched off, the mattress retains heat for 15 minutes.
Rationale 37: As per manufacturer's usage policy.
Rationale 38: If well insulated by clothes, blankets &/or swaddling, in the
ideal room temperature, will be able to maintain an adequate central
temperature.
Rationale 39: The head has a large surface area for heat loss so should be
covered. (Ref15)
Rationale 40: The environmental temperature must be altered slowly due to the
immature heat conserving mechanisms at this age and limited ability to adapt to
sudden or extreme changes.
Rationale 41: To prevent heat loss by all means (Altimier et al 1999).
Rationale 42: To provide optimal insulation.
Rationale 43: To prevent heat loss during transfer/change to the Neutral
Thermal Environment (Altimier et al 1999)
Rationale 44: To maintain a NTE at all times (Merenstein & Gardiner 1998).
Rationale 45: To prevent the neonate being exposed to a cold, wet surface and
losing heat by conduction and evaporation
Rationale 46: To evaluate the effectiveness of interventions.
Rationale 47: To provide an accurate record.
Rationale 48: In enable quick recognition and prevention of adverse
consequences (Mitchell 1997).
Rationale 49: To avoid the complications of cold stress.
Rationale 50: To decrease surface area for heat loss.
Rationale 51: It could be due to vasoconstriction from shock, hypovolaemia,
post-operative stress or handling.
Rationale 52: To enable quick recognition and prevention of adverse consequences
(Mitchell 1997).
Rationale 53: To avoid the complications of heat stress.
References/Bibliography
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