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THERMOREGULATION IN THE THERMOREGULATION IN THE NEONATENEONATE

Mary Mary DeBarbieris, DeBarbieris,

RNCRNCOctober, October,

20082008

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Why Worry About Thermoregulation?

Body temperature is one of the primary vital signs. In terms of ABC’s think:A - AirwayB - BreathingC - CirculationD - Degrees

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Goal of Thermoregulation

Maintain correct body temperature range in order to:

maximize metabolic efficiencyreduce oxygen useprotect enzyme functionreduce calorie expenditure

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Challenges of thermoregulation in

Neonatal carePrior to delivery infants do not maintain temperature independentlyInfant’s in-utero temp is generally 0.5˚C higher than mother’s tempRapid cooling occurs after delivery

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Neurologic adaptation: Thermoregulation

Maintenance of body temp is a major task Skin is thin & blood vessels are close to the surfaceHave little subcutaneous fat to serve as barrier to heat lossTerm Infants have 3x the surface to body mass of an adultPreterm infants and SGA infants have 4x the surface mass to body mass of an adultPreterm infants are especially susceptible to heat loss due to poor tone, fat and thinner skin than term infants

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DefinitionsTo understand the role of thermoregulation in the care ofinfants, we need to understand a fewsimple definitions.

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Neutral Thermal Neutral Thermal TemperatureTemperature

A neutral thermal temperature isthe body temperature at which anindividual's oxygen use and energyexpenditure are minimized.

Minimal metabolic rateMinimal metabolic rateMinimal oxygen consumptionMinimal oxygen consumption

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Body temperature in the newborn infant

Classification of hypothermia is based on core temperature

NORMAL – 36.5 to 37.3˚C (97.7 –99.2˚F)Cold Stress 36.0 to 36.4˚C (96.8 – 97.6 ˚F)

Cause for concernModerate hypothermia 32 –35.9˚C (89.6-96.6˚F)

Danger, warm infantSevere hypothermia – below 32˚C (89.6 ˚F)

Outlook grave, skilled care urgently needed

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Neutral Thermal Environment (NTE)

The air temperature surrounding the babysupports maintenanceof a neutral thermalbody temperature.

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ThermoneutralityThermoneutralityWhen the air temperatureis in the correct range andthe infant’s body maintainsa neutral thermaltemperature, we haveachieved thermoneutrality

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Why Are Infants At Greater Risk for

Thermoregulation Problems?

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Thermoregulation Risk Factors

PrematureSGANeuro problemsEndocrineCardiac / respiratory problemsLarge open areas in the skinSedated InfantsDrug exposure

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Why are they at Risk???Brown Adipose TissueBody surface areaSQ FatGlycogen storesBody water contentPosture

HypoxiaHypoglycemiaAnomaliesCNS Sedation

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What Do We Know?Infants have more skin surface perpound of body weight than olderchildren or adultsMore skin means more radiant heat and more insensible water loss.

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• less brown fat and glycogen stores

• decreased ability to maintain flexion

• increased body surface area compared toweight

Risk factors for Preterm Infants

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What Do We Know?The majority of an infant’sthermal receptors are foundin the face, neck, and shoulder area. Stimulation of thesereceptors will result in chillingand calorie expenditure

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What Do We Know?Shivering, which is themain way in which olderchildren and adultsgenerate heat, isimpossible or not effective in infants.Neonates and younginfants generate heat byburning brown fat.

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What do we know?Physiologic response to hypothermiaTemperature regulation controlled by hypothalamus

Activates norepinephrine release triggering

Pulmonary and peripheral vasoconstrictionIncreased pulmonary vascular resistance

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Production of HeatMetabolic ProcessesVoluntary Muscle ActivityPeripheral VasoconstrictionNonshivering Thermogenesis

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Metabolic ProcessHeat Generation by

Oxidative metabolismGlucoseFatsProtein

Metabolic Energy BrainHeartAdrenal Gland

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Voluntary Muscle Activity

Postural changesRestless movementsLimited use to Newborn

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Peripheral Vasoconstriction

Reduces skin blood flowDecreases loss of heat from the body

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Nonshivering Thermogenesis

Metabolism of brown adipose tissueInitiated in hypothalamusSympathetic nervous systemNorepinephrine release at the site of brown fat

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What is Brown Fat?Brown fat is an energy source for infantsIt can be found:

Near Kidneys and adrenalsNeck, mediastinum, scapular,

and the axilla areas. Can not be replaced once used

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Brown FatBrown FatIn full term infants brown fat is 4 % -10% of adipose deposits.In preterm infants, brown fat will not be found until 26-30 weeks gestation, and then only in small amounts.Brown fat generally disappears 3-6 months after birth, except in cold stressed infants (where it will disappear sooner.)Hypoxia causes impairment of brown fat metabolism

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So What?So What?When the air temperature

around the baby is cool,thermoreceptors in theskin are stimulated. Non-shivering thermogenesisis initiated and brown fat isburned for energy to keepthe body temperature stable.

This is the infant’s initial response.

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What Next?Conversion of brown fat

uses oxygen and glucose, therefore, the cold stressed

infant will become hypoxicand hypoglycemic.

Blood gas and glucose levelsare affected.

Growth is affected as caloriesare used to stay warmrather than grow.

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What are the Signs and Symptoms of Thermal Instability?

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Methods of heat lossPeripheral Vasodilatation

blood flowfacilitates heat transfer from periphery

to environmentSweating

evaporative heat loss postnatal age increases the ability to sweatAppears first on term newborn head

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Healthy Vs. Sick Neonate

Healthy NewbornBrown adipose tissueProduces heat and loses heat as needed

Sick or Low birth wt infants

Increased energy demandDecreased energy storeVulnerable to heat stress

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Hypothermia – Signs/symptoms

Body cool to touchMottling or pallorCentral cyanosisAcrocyanosisPoor FeedingAbdominal distensionHypotoniaHypoglycemia

gastric residualsBradycardiaTachypneaRestlessnessShallow or Irregular RespirationsApneaLethargy

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Signs and Symptoms of Hypothermia in Infants

Vasoconstriction Peripheral vasoconstriction occurs

in an effort to limit heat loss via blood vessels close to the skin surface. Pallor and cool skin may be noted, due to poor peripheral perfusion

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Signs and Symptoms of Hypothermia in Infants

Increased Respiratory Rate Pulmonary vasoconstriction occurs secondary to metabolic acidosis. Increasing Respiratory Distress Related to decreased surfactantproduction, hypoxia, & acidosis

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Signs and Symptoms of Hypothermia in Infants

Restlessness Restlessness may be a type of behavioral thermoregulation used to generate heat through muscle movement. The first sign may be an alteration in sleep patterns.Restlessness also indicates a change in

mental status as cerebral blood flow diminishes, due to vasoconstriction.

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Signs and Symptoms of Hypothermia in Infants

Lethargy If thermo-instability goes unrecognized, the infant will become more lethargic, as cerebral blood flow continues to diminish and hypoxemia and hypoglycemia become more pronounced.

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Signs and Symptoms of Hypothermia cont.

Metabolic Disturbances Metabolic acidosis Hypoxemia Hypoglycemia progress due to continued metabolism of brown fat, release of fatty acids and anaerobic metabolism (lactic acid)

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Signs and Symptoms of Hypothermia

Cardiac As central blood volume increases, initially

the heart rate and blood pressure increase Arrhythmias

May result from depressed myocardial contractility and irritability caused by hypothermia

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Signs and Symptoms of Hypothermia

Poor weight gain occurs when:

calories consumed brown fat stores are used to make body heat.

Poor Feeding/Weight Loss

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Even the smallestweight loss may

take days or even weeks to recover, as infants

are limited in thevolume of food theycan eat and number of calories they cantolerate.

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Consequences of Consequences of HypothermiaHypothermia

Hypoxemia from Oxygen consumptionHypoglycemia from glucose metabolismRespiratory & metabolic acidosis secondary to anaerobic metabolismInhibition of surfactant production related to acidosis

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Consequences of Hypothermia

pulmonary blood flow related to pulmonary vasoconstriction in response to body temperature pulmonary vascular resistance compromises the delivery of oxygen at the cell level risk of developing PPHN in the near term, term or post term infant

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Prevention of Hypothermia

Hypothermia can be prevented by maintaining a neutral thermal environment and reducing heat loss.A neonate is in a neutral thermal environment when the axillary temperature remains at 36.5° - 37.3° (97.7° - 99.2° F) with minimal oxygen and calorie consumption

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Prevention of Hypothermia

Reduction of heat lossConsider the four ways by which the neonate experiences heat loss and intervene appropriately.

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Prevention of Hypothermia

Prevention of hypothermia is the best treatment but if it occurs anyway, the following is a list of what you can do to relieve the cold stress.Increase ambient air temperatureApply external heat sources

Warm hatWarm blankets or diapersChemical mattress

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Prevention of Hypothermia

Avoid stressing the babyMonitor skin temperature carefully and when it normalizes remove the external heat sources one at a time to prevent rebound hypothermia

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Hyperthermia

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HyperthermiaHYPERTHERMIA also has negative consequences for the neonate.Defined as a rectal / axillary temperature greater than 37.3°c (99.2°F)

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Risk factors for Hyperthermia

Excessive environmental tempSepsisDehydrationAlterations in the hypothalamic control mechanism

Birth TraumaAnomaliesDrugs

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Signs of Hyperthermia

TachypneaApneaTachycardiaFlushingHypotensionIrritabilityPoor FeedingSkin Temp > Core Temp

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Consequences of Hyperthermia

in Metabolic rate oxygen consumptionDehydration from insensible water lossPeripheral vasodilatation/ hypotensionFluid, electrolyte abnormalitiesseizures

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There Are a Lot of Factors to Consider.How Can I Be SureMy Patient Maintains Thermoneutrality?

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It Is Important to Review and

Understand theFour Methods

of HeatTransfer

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Convection and Radiation

ConvectionOccurs when air flow carries heat to or away from the body

RadiationRadiant energyexchange occursbetween two objectsthat are not in directcontact witheach other.

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Conduction and EvaporationConduction

Heat exchange that

occurs between objects that are indirect contact with oneanother

EvaporationOccurs when liquid is turned to vapor, as withamniotic fluid on anewly deliveredinfant.

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Possible Sources of Heat Loss

58C old Items on Bed

C old Walls

C old R oom T emp.

R adiation

C old Blankets

C old X -ray plates

C old Scale

C on duc tion

Passing T raffi c

Oxygen left on

Bed Near Air Vent

C on vec tion

T achypnea

Bath

Wet Diaper

E vaporation

Baby

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Strategies to prevent heat loss:

CONVECTIVE HEAT LOSS can be prevented by:

Providing warm ambient air temperaturePlacing infants less than 1500 grams in incubatorsKeeping portholes of the incubator closedWarming all inspired oxygenOn open warmers keeping sides up and covering infant if possibleUsing Infant Servo Temperature Control

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Strategies to prevent heat loss:

RADIANT HEAT LOSS can be prevented by:

Avoiding placement of incubators, warming tables and bassinets near cold windows, walls, air conditioners, etc..Placing a knit hat on the infant’s headWrapping tiny babies in saran or “bubble” wrap environmental temperature

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Strategies to prevent heat loss:

CONDUCTIVE HEAT LOSS can be prevented by:

Placing a warm diaper or blanket between the neonate and cold surfacesPlacing infant on pre-warmed table at time of deliveryWarming all objects that come in contact with the neonateAdmitting infant to a pre-warmed Skin to skin contact

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Strategies to prevent heat loss:

EVAPORATIVE HEAT LOSS can be prevented by:

Keeping the neonate and his/her environment dry.Drying the baby immediately after delivery.Placing preterm or SGA infant in occlusive wrap/bag at deliveryDelay bath until temperature is stable

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Interventions for at Risk Infants

Pre-warmed radiant warmer bedPre-warmed incubatorDo not leave a warmer bed or incubator in the manual modeServo mode allows the baby to control the heat output of the warmer unitsHeated water padHeat lampWarm and humidify inspired gasesOcclusive wrap/bag at delivery

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Interventions for at Risk Infants

Open incubator portholes and doors only when necessaryBlanket over incubatorCluster care

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Use of Skin Servo Monitoring

Incubators and radiant warmers are designed to work using skin temperature to regulate the thermal environment

As temperature is higher in brown fat areas, avoid placing the temperature probe over brown fat deposit areas, such as the axilla, neck, or back.

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Skin servo controlIf the temperature probe is placed over brown fat deposit areas, the probe will be reading a core body temperature and not a skin temperature. As the core temperature will be higher than the skin temp., the warming

device will cool the environment. The infant will then need to burn

fat and calories to stay warm

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Temperature Probe PlacementSecure the temperature probe at/or aboutthe costal margin of the chest, midway between the xiphoid and the navel. This placement should assure accurate skintemperature measurement.Never lay infants on the probe, as this will also cause a falsely high temperature to be registered.

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Skin temperature Probes

Do Not lay infant on skin probeDo not place over:

Bony prominencesAreas of brown fat depositsPoorly vascular areasExcoriated areasKeep probe exposed to heat sourceKeep probe securely attached

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Safety ConsiderationsMake sure the sides of radiant warmers are up, unless medically unable. This protects the infant from air currents in the room that might stimulate thermal receptors.

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Interventions to ConsiderCover thermoreceptor-rich areas, such as the head.Dry well after baths, especially the head and neck area.Dress and cover infants, when in cribs, to prevent them from chilling.Warm fluids prior to dressing changesRewarm slowly to prevent a potential subsequent drop in blood pressure.

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Rewarming the Hypothermic Infant

Always be prepared to intervene Rewarm slowly (0.5˚C per hour)Monitor closely (vital signs every 15 – 30min)

Core tempSkin temp will be higher than axillaryBlood pressure

Rewarming may lead to vasodilation - hypotensionHeart rate and rhythm

Bradycardia & arrhythmias common with hypothermia

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Rewarming Monitor Respiratory rate and effort

Increased distressApnea

Oxygen saturationsHypoxemia / desaturationsBe prepared for need for respiratory supportMonitor acid/base status

Blood glucoseMonitor- infant at increase risk for hypoglycemia

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Guidelines for RewarmingIncubator better control than warmerSet temp 1 – 1.5˚C above core tempAssess infant temp every 15-30 minutesAs infants core temp reaches set temp and infant is not showing signs of deterioration increase set temp again.Continue process until temp within normal range

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Signs of Deterioration during rewarming

Tachycardia – due to in cardiac outputCardiac arrhythmiaHypotensionHypoxemia / DesaturationsWorsening respiratory distressWorsening acidosis

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Cooling the overheated neonate

Extended position- not flexedExpose skin- remove clothingKeep active temp reduction methods to a minimum to prevent dramatic heat lossMonitor temperature and VS every 15 – 30minutesBe prepared to intervene

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Preparing bag for delivery

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Key Points to Know in Preventing Hypothermia

Infant most vulnerablePremature and SGA infantsNeonates requiring prolonged resuscitation Acutely illOpen skin defects (abdomen, spine)

Remember the basicsWarm, humidified oxygen ASAPWarm objects before contact with infantPre warmed Radiant warmer/incubator – utilize servo control

Rewarm cautiously- Be prepared to resuscitate

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ConclusionsHypothermia in the newborn is due more to a lack of knowledge than to lack of equipment.Hypothermia is a preventable condition that has well documented impact on morbidity and mortality. Therefore, assisting the infant to maintain a normal body temperature and preventing hypothermia during stabilization is critical

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Thank you.