Temperature Temperature Control in the Control in the

NeonateNeonatePearl S. Park, D.O.Pearl S. Park, D.O.

PGY-2PGY-2

August 30, 2007August 30, 2007

IntroductionIntroduction Hypothermia associated w/ increased Hypothermia associated w/ increased

morbidity/mortality in newborns of all birth morbidity/mortality in newborns of all birth weights/agesweights/ages Now considered independent risk factor for Now considered independent risk factor for

mortality in pretermmortality in preterm Western philosophy of conventional care – Western philosophy of conventional care –

premature baby should bepremature baby should be Placed under radiant warmerPlaced under radiant warmer Uncovered for full visualization and to allow radiant Uncovered for full visualization and to allow radiant

heat to reach bodyheat to reach body More attn now focused on thermal care More attn now focused on thermal care

immediately after birth and during immediately after birth and during resuscitationresuscitation

Premature Susceptibility to Premature Susceptibility to Heat LossHeat Loss

High surface area to volume ratioHigh surface area to volume ratio Thin non-keratinized skinThin non-keratinized skin Lack of insulating subQ fatLack of insulating subQ fat Lack of thermogenic brown adipose Lack of thermogenic brown adipose

tissue (BAT)tissue (BAT) Inability to shiverInability to shiver Poor vasomotor responsePoor vasomotor response

ThermoregulationThermoregulation Metabolic rate of fetus per tissue wt. higher than Metabolic rate of fetus per tissue wt. higher than

adultadult Heat also transferred from mother to fetus via Heat also transferred from mother to fetus via

placenta/uterusplacenta/uterus Fetal temp consistently 0.3-0.5 deg C higher than Fetal temp consistently 0.3-0.5 deg C higher than

mother’s (always in parallel)mother’s (always in parallel) Even when mother’s temp elevates (eg fever)Even when mother’s temp elevates (eg fever)

Despite BAT in utero, fetus cannot produce extra Despite BAT in utero, fetus cannot produce extra heatheat Exposed to adenosine and prostaglandin E2 Exposed to adenosine and prostaglandin E2 inhibitors inhibitors

of non-shivering thermogenesis (NST)of non-shivering thermogenesis (NST) Metabolic adaptation for physiologically hypoxic fetus Metabolic adaptation for physiologically hypoxic fetus

since NST requires oxygenationsince NST requires oxygenation Inhibition of NST allows accumulation of BATInhibition of NST allows accumulation of BAT

ThermoregulationThermoregulation Heat gain/loss controlled by hypothalamus and Heat gain/loss controlled by hypothalamus and

limbic systemlimbic system Thermoregulatory system immature in newborns Thermoregulatory system immature in newborns

(esp premature newborn)(esp premature newborn) In term infant, response to cold stress relies on In term infant, response to cold stress relies on

oxidation of brown fat (NST)oxidation of brown fat (NST) Development begins 20th wk until shortly after Development begins 20th wk until shortly after

birth (comprises 1% body wt at that time)birth (comprises 1% body wt at that time) High concentration stored TG’sHigh concentration stored TG’s Rich capillary network densely innervated by Rich capillary network densely innervated by

sympathetic nerve endingssympathetic nerve endings Temperature sensors on posterior hypothalamus Temperature sensors on posterior hypothalamus

stimulate pituitary to produce thyroxine (T4) and stimulate pituitary to produce thyroxine (T4) and adrenals to produce norepinephrineadrenals to produce norepinephrine

Lipolysis stimulated Lipolysis stimulated energy produced in form of energy produced in form of heat in mitochondria instead of phosphate bonds by heat in mitochondria instead of phosphate bonds by uncoupling protein-1 (aka thermogenin)uncoupling protein-1 (aka thermogenin)

Risk FactorsRisk Factors

All neonates in 1st 8-12hrs of lifeAll neonates in 1st 8-12hrs of life PrematurityPrematurity SGASGA CNS problemsCNS problems Prolonged resuscitation effortsProlonged resuscitation efforts Sepsis Sepsis

Adverse Consequences of Adverse Consequences of HypothermiaHypothermia

High O2 consumption High O2 consumption hypoxia, bradycardia hypoxia, bradycardia High glucose usage High glucose usage hypoglycemia / hypoglycemia /

decreased glycogen storesdecreased glycogen stores High energy expenditure High energy expenditure reduced growth reduced growth

rate, lethargy, hypotonia, poor suck/cryrate, lethargy, hypotonia, poor suck/cry Low surfactant production Low surfactant production RDS RDS Vasoconstriction Vasoconstriction poor perfusion poor perfusion

metabolic acidosismetabolic acidosis Delayed transition from fetal to newborn Delayed transition from fetal to newborn

circulationcirculation Thermal shock Thermal shock DIC DIC death death

Modes of Heat LossModes of Heat Loss Conduction - direct heat transfer from skin to Conduction - direct heat transfer from skin to

object (eg mattress)object (eg mattress) Convection - heat loss through air flowConvection - heat loss through air flow

Also depends on air tempAlso depends on air temp Radiation - direct transfer by electromagnetic Radiation - direct transfer by electromagnetic

radiation in infrared spectrumradiation in infrared spectrum Heat gained by radiation from external radiant energy Heat gained by radiation from external radiant energy

sourcesource Heat lost by radiation to cooler walls of incubatorHeat lost by radiation to cooler walls of incubator

Evaporation - heat loss when water evaporates Evaporation - heat loss when water evaporates from skin and respiratory tractfrom skin and respiratory tract Depends on maximum relative humidity of surroundings Depends on maximum relative humidity of surroundings

less humidity = more evaporation less humidity = more evaporation

Heat Loss at BirthHeat Loss at Birth Hammarlund et al, 1980Hammarlund et al, 1980 Evaporative H20 lossEvaporative H20 loss

81-125 gm/m81-125 gm/m22/h when unwiped in ambient temp /h when unwiped in ambient temp ~25.8deg C and 42% humidity~25.8deg C and 42% humidity

Heat loss throughHeat loss through Evaporation: 60-80 W/mEvaporation: 60-80 W/m22

Radiation: 50 W/mRadiation: 50 W/m22

Convection: 25 W/mConvection: 25 W/m22

Conduction: negligibleConduction: negligible Total heat loss = 135-155 W/mTotal heat loss = 135-155 W/m22

All babies that were >3250g - body temp All babies that were >3250g - body temp decreased 0.9deg C in 15mindecreased 0.9deg C in 15min

Heat Loss at BirthHeat Loss at Birth

Hammarlund et al, 1979Hammarlund et al, 1979

Naked infants <28wks need ambient Naked infants <28wks need ambient temp ~40deg C to maintain nl temp in temp ~40deg C to maintain nl temp in 20% humidity20% humidity

Increasing humidity to 60% halved Increasing humidity to 60% halved losseslosses

Attempt to Overcome Attempt to Overcome LossesLosses

Radiant heaters insufficient to warm Radiant heaters insufficient to warm preterm babypreterm baby Esp during resuscitationEsp during resuscitation 750g baby w/ surface area of ~ 0.06m750g baby w/ surface area of ~ 0.06m22

requires at least 9.3W to compensate requires at least 9.3W to compensate for losses at birthfor losses at birth

At mattress lvl, max of 9W absorbed by At mattress lvl, max of 9W absorbed by baby if radiant heat absorbed by, at baby if radiant heat absorbed by, at least, 50% of mattressleast, 50% of mattress

Thermoneutral Thermoneutral EnvironmentEnvironment

Temp and environmental conditions Temp and environmental conditions at which metabolic rate and O2 at which metabolic rate and O2 consumption are lowestconsumption are lowest

Silverman et alSilverman et al Maintaining constant abdominal skin Maintaining constant abdominal skin

temp b/w 36.2-36.5 deg C optimaltemp b/w 36.2-36.5 deg C optimal WHO classification of hypothermiaWHO classification of hypothermia

Mild: 36-36.4deg CMild: 36-36.4deg C Mod: 32-35.9deg CMod: 32-35.9deg C Severe: <32deg CSevere: <32deg C

Kangaroo Mother Care Kangaroo Mother Care (KMC)(KMC)

Introduced in 1983 by Rey and Martinez Introduced in 1983 by Rey and Martinez in Colombiain Colombia LBW infants nursed naked (wearing only cloth LBW infants nursed naked (wearing only cloth

diaper) between mothers’ breastsdiaper) between mothers’ breasts Data from other countries show infants nursed Data from other countries show infants nursed

by KMC haveby KMC have Fewer apneic episodesFewer apneic episodes Similar or better blood oxygenationSimilar or better blood oxygenation Lower infxn rtesLower infxn rtes Are alert longer and cry lessAre alert longer and cry less Are breastfed longer and have better bondingAre breastfed longer and have better bonding Improved survival in low-resource settingsImproved survival in low-resource settings

KMCKMC Bergman et al, 2004Bergman et al, 2004

Randomized controlled trial comparing KMC to Randomized controlled trial comparing KMC to pre-warmed servo-controlled closed incubator pre-warmed servo-controlled closed incubator after birthafter birth

20 infants b/w 1200-2199g using KMC vs 14 20 infants b/w 1200-2199g using KMC vs 14 controlscontrols

Excluded if C-sec, mother too ill to look after self/infant, Excluded if C-sec, mother too ill to look after self/infant, known HIV, BW outside 1200-2199g, 5min Apgar <6, known HIV, BW outside 1200-2199g, 5min Apgar <6, congenital malformationscongenital malformations

1/20 subjects vs 8/14 controls had initial temps < 1/20 subjects vs 8/14 controls had initial temps < 35.5deg C (P = 0.006)35.5deg C (P = 0.006)

1/20 subjects vs 3/14 controls had bl glucoses < 1/20 subjects vs 3/14 controls had bl glucoses < 2.6 mmol/L (though 40mg/dL = 2.2mmol/L)2.6 mmol/L (though 40mg/dL = 2.2mmol/L)

Stability of cardio-respiratory system in preterm Stability of cardio-respiratory system in preterm infants (SCRIP) score was 2.88 points higher w/in infants (SCRIP) score was 2.88 points higher w/in 1st 6hrs in KMC group (95% CI 0.3-5.46)1st 6hrs in KMC group (95% CI 0.3-5.46)

SCRIP ScoreSCRIP Score

SCRIPSCRIP 22 11 00

HRHR RegularRegular Decel to 80-Decel to 80-100100

Rte <80 or Rte <80 or >200 bpm>200 bpm

RRRR RegularRegular Apnea <10s Apnea <10s or periodic or periodic breathingbreathing

Apnea >10s Apnea >10s or or

tachypnea tachypnea >80 >80

OO22 sat sat >89%>89% 80-89%80-89% <80%<80%

Barriers to Heat LossBarriers to Heat Loss Cochrane database reviewCochrane database review 4 studies compared barriers to heat loss vs. no 4 studies compared barriers to heat loss vs. no

barriersbarriers 2 comparison subgroups2 comparison subgroups

Plastic wrap/bag vs routine carePlastic wrap/bag vs routine care Stockinet cap vs routine careStockinet cap vs routine care

Plastic wrap/bag vs routine carePlastic wrap/bag vs routine care 3 studies involving 200 infants all <36wks3 studies involving 200 infants all <36wks All placed under radiant warmer, wrapped to shoulders All placed under radiant warmer, wrapped to shoulders

while still wet, heads dried and resuscitated according while still wet, heads dried and resuscitated according to guidelines to guidelines

GA <28wks: wrap group had temps 0.76deg C higher GA <28wks: wrap group had temps 0.76deg C higher than controls (95% CI 0.49-1.03)than controls (95% CI 0.49-1.03)

GA 28-31wks: no statistical difference GA 28-31wks: no statistical difference

Barriers to Heat LossBarriers to Heat Loss

Plastic wrap/bag vs routine care (cont)Plastic wrap/bag vs routine care (cont) 1hr after admission for GA <28wks, no 1hr after admission for GA <28wks, no

statistical difference (though direction was in statistical difference (though direction was in favor of intervention)favor of intervention)

Plastic wrap significantly reduced risk of Plastic wrap significantly reduced risk of hypothermia (core temp <36.5deg C) on hypothermia (core temp <36.5deg C) on admission to NICUadmission to NICU

RR 0.63 (95% CI 0.42-0.93)RR 0.63 (95% CI 0.42-0.93) NNT found to be 4 (95% CI 3-17) - so 4 infants would NNT found to be 4 (95% CI 3-17) - so 4 infants would

need to be wrapped in plastic to prevent 1 from need to be wrapped in plastic to prevent 1 from becoming hypothermicbecoming hypothermic

No significant differences found in duration of No significant differences found in duration of OO22 therapy, major brain injury, duration of therapy, major brain injury, duration of hospitalization, or deathhospitalization, or death

Barriers to Heat LossBarriers to Heat Loss Stockinet cap vs routine careStockinet cap vs routine care

1 study involving 40 AGA infants w/ GA’s 32-36wks1 study involving 40 AGA infants w/ GA’s 32-36wks Exclusion critera: 5min Apgar <7, SSx CNS Exclusion critera: 5min Apgar <7, SSx CNS

defect, sepsis, or maternal temp >37.8deg C defect, sepsis, or maternal temp >37.8deg C during laborduring labor

Cap group had caps placed ASAP after drying Cap group had caps placed ASAP after drying under radiant warmer and infants <2500g were under radiant warmer and infants <2500g were transported in incubatortransported in incubator

BW <2000g: Cap group had core temps 0.7deg C BW <2000g: Cap group had core temps 0.7deg C higher than control (95% CI -0.01-1.41) - higher than control (95% CI -0.01-1.41) - borderline statistical differenceborderline statistical difference

BW >/= 2000g: no sig difBW >/= 2000g: no sig dif No sig dif in preventing hypothermiaNo sig dif in preventing hypothermia

External Heat SourcesExternal Heat Sources

Cochrane database reviewCochrane database review 2 studies compared external heat 2 studies compared external heat

sources to routine caresources to routine care 2 comparison subgroups2 comparison subgroups

Skin-to-skin vs routine care (already Skin-to-skin vs routine care (already mentioned)mentioned)

Transwarmer mattress vs routine careTranswarmer mattress vs routine care

External Heat SourcesExternal Heat Sources Brennan et al, 1996Brennan et al, 1996 24 infants w/ BW </= 1500g24 infants w/ BW </= 1500g Transport Mattress (TM) - made of sodium Transport Mattress (TM) - made of sodium

acetate - activated to ~40deg C when delivery acetate - activated to ~40deg C when delivery imminentimminent Infant placed upon blankets covering mattress, Infant placed upon blankets covering mattress,

dried, then placed on TM directlydried, then placed on TM directly Control group = same intervention but w/o Control group = same intervention but w/o

TMTM Both groups resuscitated according to Both groups resuscitated according to

guidelines then transferred to NICU on guidelines then transferred to NICU on radiant warmer surface radiant warmer surface

External Heat SourcesExternal Heat Sources

Brennan et al, contBrennan et al, cont Increase of 1.6deg C in TM group Increase of 1.6deg C in TM group

(95% CI 0.83-2.37)(95% CI 0.83-2.37) Evidence suggests that TM Evidence suggests that TM

significantly reduces risk of significantly reduces risk of hypothermia w/ RR 0.3 (95% CI 0.11-hypothermia w/ RR 0.3 (95% CI 0.11-0.83)0.83) NNT = 2 (95% CI 1-4)NNT = 2 (95% CI 1-4)

No adverse occurrences reported in No adverse occurrences reported in this study, though other studies have this study, though other studies have had infants sustain 3rd deg burnshad infants sustain 3rd deg burns

In ConclusionIn Conclusion Plastic barriers effective in reducing heat loss in Plastic barriers effective in reducing heat loss in

newborns <28wks newborns <28wks No evidence yet to suggest plastic barriers No evidence yet to suggest plastic barriers

decrease duration of Odecrease duration of O22 therapy, hospitalization, or therapy, hospitalization, or incidence of major brain injury/deathincidence of major brain injury/death

Stockinet caps effective in reducing hypothermia in Stockinet caps effective in reducing hypothermia in newborns <2000g, but not >/= 2000gnewborns <2000g, but not >/= 2000g

KMC shown to be effective in stable newborns KMC shown to be effective in stable newborns down to 1200g in reducing risk of hypothermiadown to 1200g in reducing risk of hypothermia

TM decreases incidence of hypothermia </= 1500gTM decreases incidence of hypothermia </= 1500g In the end, the smaller the baby, the more likely In the end, the smaller the baby, the more likely

any intervention will be of benefitany intervention will be of benefit

Areas of Further StudyAreas of Further Study Need more studies w/ larger Need more studies w/ larger

population basespopulation bases Short- and long-term outcomes need Short- and long-term outcomes need

to be studied further (especially w/ to be studied further (especially w/ neurdevelopmental F/U)neurdevelopmental F/U)

Secondary outcomes that need Secondary outcomes that need further study:further study:HypoglycemiaHypoglycemia RDSRDS Intubation/Intubation/

ve-ntilationve-ntilationLength of Length of staystay

Metabolic Metabolic acidosisacidosis

ARFARF GrowthGrowth Adverse Adverse eventsevents

Neonatal Energy Neonatal Energy TriangleTriangle

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