Clinical Guidelines (Nursing)

Thermoregulation in the Preterm Infant

  • Introduction

    Temperature control in the infant is a critical physiological function that is strongly influenced by physical immaturity, illness and environmental factors. Both hypothermia and hyperthermia should be avoided as they can have severe adverse outcomes and can increase morbidity and mortality. Maintaining correct body temperature maximizes metabolic efficiency, decreases oxygen use, protects enzyme function and decreases caloric expenditure.

    Aim

    The aim of this guideline is to provide staff with knowledge regarding thermoregulation in the preterm infant.  This will optimise health and wellbeing outcomes by providing care that is research based, clinically effective and safe.

    Definition of Terms 

    • Thermoregulation The ability to balance heat loss and heat production through normal thermoregulatory mechanisms in order to maintain body temperature within a normothermic range.
    • Neutral Thermic Environment (NTE) This is the environment, specifically the environmental temperature, in which the infant is able to maintain a normal temperature with a minimal metabolic rate and therefore minimal oxygen consumption.  
    • Normothermic temperature range 36.5°C – 37.5°C
    • Hypothermia When the infants’ temperature drops below that required for normal metabolic and body function (< 36.5°C)
    • Hyperthermia When the infant’s body absorbs or produces more heat than it can dissipate (> 37.5°C).
    • Fever Is caused by a change in the body’s temperature set point and differs from hyperthermia in the mechanism that causes the elevation in temperature. It is usually as a result of an inflammatory response. A temperature ≥ 38°C in an infant is considered to be a “fever”.

    Background Information

    Modes of Heat Loss:

    • Evaporation - Heat loss occurring during conversion of liquid to vapour
    • Convection - Transfer of heat from the body surface to the surrounding air via air current
    • Conduction - Transfer of heat from one solid object to another solid object in direct contact with it
    • Radiation - Transfer of heat to cooler solid objects not in direct contact with the body

    It is important to note that preterm infants are at a higher risk of heat loss via the 4 modes mentioned above.  Preterm infants possess a disproportionate body mass-to-surface area ratio, reduced thermal insulation in decreased brown adipose tissue (BAT), a thin epidermis that has increased permeability, poor vasomotor control and a naturally extended position that exposes a greater body surface area to the external environment.  For these infants, cold stress will trigger a cascade of physiological responses that further impedes their transition to extrauterine life.
    Cold Stress:
    Cold Stress is a cascade of physiological events caused by the infant’s use of chemically mediated thermogenesis in attempt to increase core temperature. Two specific alterations to thermogenesis occur in the infant suffering cold stress; vasoconstriction of the peripheries, which allows heat to be drawn back to the core and metabolism of BAT, which is described here.
    Metabolism of Brown Adipose Tissue:
    Within the metabolism of BAT during states of cold stress, a cascade of metabolic and chemical reactions are initiated and maintained, which result in a number of detrimental physiological changes (depicted below).

    Environmental Humidity: 
    Infants born at <30 weeks gestation have an immature epidermis and stratum corneum and are at an increased risk of transepidermal water loss (TEWL).  The use of environmental humidity assists to reduce TEWL and in turn supports temperature regulation, fluid and electrolyte management and skin integrity (See Environmental Humidity Guideline).

    Equipment

    • Incubator: All preterm infants ≤32 weeks gestation or ≤1800 grams should be cared for in an incubator wherever possible. The two modes used when nursing a preterm infant in an incubator are servo control or manual control. Servo control is the preferred method at all times (see Management). The incubator needs to be changed every 7 days when humidification is in use and every 14 days otherwise
    • Radiant Warmer: Preterm infants should only be nursed on a radiant warmer in preparation for theatre or in the event of multiple procedures that are unable to be undertaken in an incubator without loss of substantial heat (See Surgical Procedures within the NNU Guideline).
    • Open Cot: Preterm infants weighing ≥1800 grams with a stable temperature (3 consecutive axillary temperatures above 36.5°C in an incubator of <28°C) may be transferred to an open cot. 

    Perspex cots are preferential in the preterm infant to prevent heat loss due to their enclosed design. However, limitations pertaining to access and procedures do exist and in this case the patient may need to remain in an incubator at low temperature for longer if they cannot maintain their temperature in a regular paediatric metal cot.  

    Assessment

    Frequency of Temperature Assessment:

    • Hourly until stable for 4 hours on:
      • Admission
      • Transfer to incubator, radiant warmer or open cot
      • Commencement or cessation of phototherapy
      • Commencement or cessation of humidity
      • Commencement or cessation of servo control
    • When infant’s temperature is stable (for at least 4 hours prior):
      • 6 – 8 hourly
    • Exceptions:
      • 4 hourly for the first 24 hours when manual control is commenced, then 6-8 hourly
      • 4 hourly for the first 24 hours when transferred to an open co
      • If temperature records outside normal range, commence hourly temperatures until 2 consecutive normothermic measurements (Refer below for Temperature outside of Normothermic Range)
      • Infants on Neonatal Abstinence Syndrome (NAS) scoring charts require a temperature check a minimum 4 hourly or otherwise prior to each feed

    Method of Temperature Assessment:

    Rectal Temperature is taken on admission of a newborn to establish baseline core temperature as well as patency of anus.

    1. Place plastic sheath over thermometer
    2. Dab a small amount of lubrication on end of thermometer
    3. Insert thermometer 1cm into infant’s anus (2cm for term infant)
    4. Turn thermometer on
    5. Wait for 5 seconds post Celsius sign flashing
    6. Remove thermometer
    7. Clean with alcohol

    Axilla Temperature is taken thereafter the initial rectal temperature. 

    1. Position the tip of the thermometer in the middle of the axilla
    2. Turn thermometer on
    3. Wait for 5 seconds post Celsius sign flashing
    4. Remove thermometer

    Skin Probe Temperature measures the infant’s skin temperature when utilising servo control and assists the incubator in adjusting heat output based on the ‘set’ skin temperature and the ‘actual’ skin temperature.

    1. Place probe on clean dry skin position over soft tissue
    2. Ensure the probe is secure to avoid inaccurate readings. A small amount of tape may be used to stabilise probe however consideration must be given to skin integrity
    3. Avoid laying the infant on the skin temperature probe, to both reduce inaccurate readings and prevent pressure areas
    4. Infants weighing <1750grams – set skin temperature at 36.8°C
    5. Infants weighing >1750grams – set skin temperature at 36.5°C
    6. Alter skin probe position every 6-8 hours (see Neurodevelopmental Care for the Preterm Infant Guideline)

    Temperature Outside of Normothermic Range

    • If the patient’s temperature is <36.5°C, initiate the following:
      • Increase cot temperature by 0.5°C hourly
      • Check axillary temperature hourly until 2 consecutive temperature of 36.5°C or above are recorded
      • If the patient does not require close observation then layers (clothes & wraps) can be added but careful consideration needs to be given in blocking the transfer of heat and exacerbating the effects of conduction if the wraps/clothes are not pre-warmed.
    • If the patient’s temperature is >37.5°C, initiate the following:
      • Assess environmental factors
      • Assess physiological factors
      • Decrease cot temperature by 0.5°C hourly
      • Check axillary temperature hourly until 2 consecutive temperatures <37.5°C.
      • Consider whether this is an indication that the infant requires the incubator temperature to be weaned
    • Considerations:
      • Only ever alter incubator temperature by 0.5°C at any one time and allow at least one hour for the infant’s temperature to stabilise before making further changes
      • Manipulation of incubator temperatures may obscure temperature instability associated with physiological features rather than environmental i.e. infection. This may put infants at risk of being nursed in inappropriately cold temperatures.
      • NEVER switch the incubator off, as the fan does not work when the incubator is switched off. Once the incubator is switched off there is no circulation of air and therefore carbon monoxide levels increase.  Please note that transfer of patients from room-to-room, out of the ward, etc. is an exemption to the rule however, the duration in which the incubator is switched off needs to be minimised
      • Inform AUM and/or Medical Team of any significant changes or concerns

    Documentation

    Within the flowsheets of EMR, temperatures can be documented within the ‘observations’ section with the method of temperature selected from the drop down options below.  Furthermore, within ‘thermoregulation’, select either incubator or radiant warmer, and document the ‘skin temperature probe reading’, ‘skin temperature site’ and ‘set temperature/air temperature’ hourly.

    Management

    Manual Control:
    This requires one constant environmental temperature to be set. This mode is used in the more stable late preterm infant where minute adjustments are not required. 

    Servo Control:
    This is the preferred setting used to nurse preterm infants as it automatically and constantly adjusts the incubator heat output according to the skin temperature set and the skin temperature measured from the skin temperature probe. The infant’s skin temperature is continuously monitored via the temperature skin probe. 

    Cessation of servo control can be considered when the infant:

    • Weighs ≥1000grams
    • Is stable in an incubator or radiant warmer temperature of <34.0°C
    • Is no longer requiring environmental humidity

    When transferring an infant from servo to manual control, set the air temperature at the same temperature that was delivered over the previous 24 hours. If there have been significant fluctuations, consider if the infant is ready to be transitioned to manual control.

    Weaning Incubator Temperature:
    Weaning of the incubator temperature may take place under a number of circumstances and is to be considered by the bedside nurse when an infant is being nursed with the Manual Control setting. Circumstances may include environmental, physiological and maturity.

    • Assess all possible environmental and physiological factors including maturity
    • Assess appropriate temperature range for gestation and current age (See Neutral Thermal Environment Chart)
    • Wean the incubator temperature by 0.5°C hourly (at a maximum)
    • Check axillary temperature hourly for four hours with each change

    Transfer to an Open Cot:
    Preterm infants can be transferred to an open cot once they have met the following criteria:

    • Weight ≥1800 grams
    • Consistent weight gain 
    • Stabilized apnoeic and bradycardic episodes 
    • Medically stable condition 
    • No longer requiring invasive mechanical ventilation 

    Once the preterm infant meets the above criteria and discussion has taken place between the bedside nurse, medical team & AUM, the infant may be transferred to an open cot by using the following steps as a guide:

    • Referring to the Neutral Thermal Environment chart, wean incubator temperature by 0.5°C hourly (as a maximum) until the temperature is at the lowest level of the appropriate neutral thermal rang
    • Dress infant in pre-warmed clothing and wrap  
    • Ensure the infant maintains their temperature at this set temperature for 4 hours (hourly axilla temperatures)
    • Place in open cot (preferably a Perspex cot)
    • Assess temperature
    • If the axillary temperature drops between 36.2°C and 36.5°C, increase clothing layers if possible and add a pre-warmed wrap/blanket. 
    • Check temperature hourly until stable for 4 consecutive hours 
    • If the axilla temperature remains unstable for a consecutive period of 3 hours (3 x hourly checks) then return the infant to a pre-warmed incubator.

    Links

    Evidence Table

    The evidence table for this guideline can be viewed here

    References 

    • Auckland District Health Board Newborn Services – Thermal Environment and Growth in Preterm Infants (2001).
    • Gray, P., & Flenady, V. (2011) Cot-nursing versus incubator care for preterm infants. Cochrane Database of Systematic Reviews 2011, Issue 8. Art. No.: CD003062. DOI: 10.1002/14651858.CD003062.pub2
    • Mercy Hospital for Women - Thermoregulation of the Neonate Clinical Guideline (2009).
    • Merenstein, G., & Gardner, S. (2011), Handbook of Neonatal Intensive Care, 7th Edition.
    • New, K., Flenady, V., & Davies, M. (2011).  Transfer of preterm infants from incubator to open cot at lower versus higher body weight. Cochrane Database of Systematic Reviews 2011, Issue 9. Art. No.: CD004214. DOI: 10.1002/14651858.CD004214.pub4
    • The Royal Children’s Hospital, Melbourne – Temperature Management Clinical Guideline (2014).
    • The Royal Women’s Hospital, Melbourne – Thermoregulation for a Baby Clinical Guideline (2014).
    • Pate, M. (2001). Thermoregulation. In Curley, M., & Moloney-Harmon, P. (Eds.), Critical Care Nursing of Infants and Children (pp. 443 – 459). Philadelphia: W.B. Saunders Co.
    • Sinclair, J. (2002). Servo-control for maintaining abdominal skin temperature at 36C in low birth weight infants. Cochrane Database of Systematic Reviews 2002, Issue 1. Art. No.: CD001074. DOI: 10.1002/14651858.CD001074
    • World Health Organisation (1997). Thermal Protection of the Newborn: A Practical Guide. Retrieved from: http://passthrough.fwnotify.net/download/016828/http://apps.who.int/iris/bitstream/10665/63986/1/WHO_RHT_MSM_97.2.pdf


    Please remember to read the disclaimer.

     

    The development of this nursing guideline was coordinated by Alanah Crowle, RN, Butterfly Ward, and approved by the Nursing Clinical Effectiveness Committee. Updated November 2016.