thermoregulation in the newborn audra mccay prince, md assistant professor of pediatrics arkansas...
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Thermoregulation in the Newborn
Audra McCay Prince, MDAssistant Professor of Pediatrics
Arkansas Children’s Hospital & UAMS Neonatology
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Heat Production
Voluntary muscle activityInvoluntary muscle activity (shivering)Non-shivering Thermogenesis
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Brown Fat
LocationsAbundance in infancyDiffers morphologicallyDiffers metabolicallySympathetic enervation
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Mechanisms for Heat Loss
ConductionConvectionRadiationEvaporation
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Conductive Heat Loss
This is heat transfer from a warmer object to a cooler object that it is in contact with.
Example: the baby loosing heat to a cold mattress or scale.
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Convective Heat Loss
This is heat transfer from a warmer object to the cooler air. It depends on air flow, as well as the temperature of the air.
Example: the baby on a radiant warmer can have a large amount of convective heat loss, especially in the drafty areas of the nursery.
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Radiant Heat Loss
This is heat transfer from a warmer object to a cooler object that are NOT in contact with each other.
Example: heat loss to the walls of the isolette, or heat loss to a cold window next to a crib in the nursery
Transport isolettes
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Evaporative Heat Loss
Cooling of the body by the evaporation of water from the skin.
In very small infants this is increased during the first few days of life due to their very thin (non-keratinized) skin, an increased body surface area/body mass ratio, and the extracellular mass is between 80-90% H2O.
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Relative Role of Evaporative Heat Loss
0
10
20
30
40
50
60
.88-1.25 1.25-1.75 1.75-2.25 2.25-2.88
Total heat productionEvaporative heat loss
Birthweight (kg)
Kca
l/kg
/da
y
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Environmental Temperature
Heat Production orO2 Consumption
Decreasing Body Temp
SummitMetabolism
Zone ofThermalNeutrality
IncreasingBody Temp
Death fromHeat
Mernstein G, Blackmon L 1971
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BodyTemperature
37 C
InevitableBody
Cooling
ThermoregulatoryRange
Inevitable
BodyHeating
Zone ofThermal
Neutrality
Merenstein G, Blackmon L, 1971
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Homeotherm
Homeotherms possess mechanisms that enable them to maintain body temperature at a constant level more or less accurately despite changes in the environmental temperature.
An infant that is cooled and not hypoxic attempts to maintain body temperature by increasing the consumption of calories and oxygen to produce additional heat.
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BodyTemperature
37 C
InevitableBody
Cooling
ThermoregulatoryRange
Inevitable
BodyHeating
Zone ofThermal
Neutrality
Merenstein G, Blackmon L, 1971
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Temperature Measurements
Skin temperatureServo ControlAxillary temperatureRectal temperature
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Specific Situations
In UteroDelivery RoomIsoletteRadiant WarmerOpen Crib
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In Utero
Heat produced in the fetus is dissipated through the placenta to the mother
Fetal temp normally 0.6 0 higher than the mother’s temp
Maternal feverEpidural anesthesia
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Delivery Room
The fetus is born into a cold wet environment, and no longer has the maternal heat reservoir.
When skin is 1st exposed to the air, rapid cooling begins with body temp dropping from 0.2-1.0 c/min.
In response to cold a nor-adrenaline surge occurs. When pursued to an extreme peripheral and pulmonary vasoconstriction occur with sub-sequent decreases in oxygenation and perfusion.
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Delivery Room
Careful and immediate drying of the infant’s entire body remains critical in minimizing evaporative heat loss.
Placing on radiant warmerHatsMaternal skin
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Your Mother was Right
Care of the High-Risk Neonate, 4th Edition, Klaus and Fanaroff, 1993, pg 122
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Isolette
The importance of double wallsTransport isolettesSkin temp v. Air tempNever cover temp probesPlacement of probe is important
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Double Walled Isolettes
Care of the High-Risk Neonate, 4th Edition, Klaus and Fanaroff, 1993, pg 119
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Radiant Warmer
Must use a metallic coverAir flow is importantSaran wrapDrapes
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Open Crib
Remember that babies continue to have radiant heat loss to the windows, walls, etc., If they are not bundled.
Babies that are losing weight, ex. Feeders and growers may be cold with increased oxygen consumption and caloric expenditure.
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Disorders of Temperature Regulation
HypothermiaNeonatal Cold InjuryHyperthermiaAsphyxia
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Hypothermia
Low birth weight infantsAsphyxiaPrematuritySepsisCNS
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Neonatal Cold Injury
LBW Lethargic and feed poorly Cold to touch Red baby Slow and grunting respirations with bradycardia edema and sclerema Metabolic derangements Pulmonary hemorrhage
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Treatment of Cold Injury
Re-warmingOxygenGlucoseNaHCO3
NPOAntibiotics
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Causes of Hyperthermia
Environmental temperatureInfectionDehydrationCerebral birth traumaDrugs
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Asphyxia
ResuscitationInability to regulate tempPay attention to heat loss
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Conclusion
Attentiveness to temperature in a sick newborn is extremely important.
Minimizing O2 consumption is the goal.
Recognition and treatment of infants with cold injury can be life saving.