Infant Thermoregulation

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

• draughts
• windows

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

Reference 1:
Thomas K (1994) Thermoregulation in neonates. Neonatal Netw 13 (2): 15-22.

Reference 2:
Merenstein GB, Gardiner SI (1998) Handbook of Neonatal Intensive Care 3rd Edition. St Louis, Mosby

Reference 3:
Leick-Rude MK, Bloom LF (1998) A comparison of temperature-taking methods in neonates. Neonatal Netw 17 (5): 21-37.

Reference 4:
Pontious S, Kennedy AH, Shelley S, Mittrucker C (1994) Accuracy and reliability of temperature measurement by instrument and site. J Pediatr Nurs 9 (2): 114-23.

Reference 5:
Sheeran MS (1996) Thermoregulation in Neonates: obtaining an accurate axillary temperature measurement. Journal of Neonatal Nursing 2(4): 6-9.

Reference 6:
Mok Q, Bass CA, Ducker DA, McIntosh N (1991) Temperature instability during nursing procedures in preterm neonates. Arch Dis Child 66 (7 Spec No): 783-6.

Reference 7:
Lyon AJ, Pikaar ME, Badger P, McIntosh N (1997) Temperature control in very low birthweight infants during first five days of life. Arch Dis Child Fetal Neonatal Ed 76 (1): F47-50.

Reference 8:
Drager Product Information (1997) Closed and open incubators. Hemel Hempstead, Drager

Reference 9:
Mitchell A (1997) Thermal monitoring of patients in NICU. Journal of Neonatal Nursing 2(2): Insert (i-iv).

Reference 10:
Blackburn ST, Loper DL (1992) Thermoregulation Blackburn ST, Loper DL In: Maternal, Fetal and Neonatal Physiology: A Clinical Perspective. London, WB Saunders

Reference 11:
Marshall A (1997) Humidifying the Environment for the Premature Neonate. Journal of Neonatal Nursing 3(1): 32-36.

Reference 12:
Seguin JH, Vieth R (1996) Thermal stability of premature infants during routine care under radiant warmers. Arch Dis Child Fetal Neonatal Ed 74 (2): F137-8.

Reference 13:
Roberton NRC (1995) A Manual of Neonatal Intensive Care. London, Edward Arnold

Reference 14:
Medoff-Cooper B (1994) Transition of the preterm infant to an open crib. J Obstet Gynecol Neonatal Nurs 23 (4): 329-35.

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Short MA (1996) A comparison of temperature in VLBW infants swaddled versus unswaddled. Neonatal Network 17(3): 25-31.

Reference 16:
Altimier I, Warher B, Amlung S, Kenner C (1999) Neonatal Thermoregulation: Bed Surface Transfers. Neonatal Network 18(4): 35-37.

Reference 17:
Klaus M, Fanaroff A (1973) The Physical Environment in Care of the High Risk Neonate. Philadelphia, Saunders

Reference 18:
Sedin G (1995) Neonatal heat transfer, routes of heat loss and heat gain. Okken A and Koch J In: Thermoregulation of sick and low birthweight neonates. Berlin, Germany, Springer-Verlag

Reference 19:
Knobel R, Holditch-Davis D (2007) Thermoregulation and heat loss prevention after birth and during neonatal intensive-care unit stabilization of extremely low-birthweight infants. J Obstet Gynecol Neonatal Nurs 36 (3): 280-7.

Reference 20:
Harpin VA, Rutter N (1985) Humidification of incubators. Arch Dis Child 60 (3): 219-24.

Reference 21:
GE Healthcare (2011) giraffe omnibed. www.gehealthcare.com/euen/maternal-infant-care/products/microenvironments/giraffe_omnibed/index.html.