Transcript Temperature Control in the Neonate Pearl S. Park, D.O. PGY-2 August 30, 2007 Introduction  Hypothermia associated w/ increased morbidity/mortality in newborns of all birth weights/ages   Western philosophy of.

Temperature Control
in the Neonate
Pearl S. Park, D.O.
PGY-2
August 30, 2007
Introduction
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Hypothermia associated w/ increased
morbidity/mortality in newborns of all birth
weights/ages
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Western philosophy of conventional care – premature
baby should be
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Now considered independent risk factor for mortality in
preterm
Placed under radiant warmer
Uncovered for full visualization and to allow radiant heat to
reach body
More attn now focused on thermal care immediately
after birth and during resuscitation
Premature Susceptibility to Heat
Loss
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High surface area to volume ratio
Thin non-keratinized skin
Lack of insulating subQ fat
Lack of thermogenic brown adipose tissue
(BAT)
Inability to shiver
Poor vasomotor response
Thermoregulation
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Metabolic rate of fetus per tissue wt. higher than adult
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Fetal temp consistently 0.3-0.5 deg C higher than
mother’s (always in parallel)
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Heat also transferred from mother to fetus via
placenta/uterus
Even when mother’s temp elevates (eg fever)
Despite BAT in utero, fetus cannot produce extra heat
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Exposed to adenosine and prostaglandin E2  inhibitors of
non-shivering thermogenesis (NST)
Metabolic adaptation for physiologically hypoxic fetus since
NST requires oxygenation
Inhibition of NST allows accumulation of BAT
Thermoregulation
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Heat gain/loss controlled by hypothalamus and limbic
system
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Thermoregulatory system immature in newborns (esp
premature newborn)
In term infant, response to cold stress relies on
oxidation of brown fat (NST)
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Development begins 20th wk until shortly after birth
(comprises 1% body wt at that time)
High concentration stored TG’s
Rich capillary network densely innervated by sympathetic
nerve endings
Temperature sensors on posterior hypothalamus stimulate
pituitary to produce thyroxine (T4) and adrenals to produce
norepinephrine
Lipolysis stimulated  energy produced in form of heat in
mitochondria instead of phosphate bonds by uncoupling
protein-1 (aka thermogenin)
Risk Factors
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All neonates in 1st 8-12hrs of life
Prematurity
SGA
CNS problems
Prolonged resuscitation efforts
Sepsis
Adverse Consequences of
Hypothermia
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High O2 consumption  hypoxia, bradycardia
High glucose usage  hypoglycemia / decreased
glycogen stores
High energy expenditure  reduced growth rate,
lethargy, hypotonia, poor suck/cry
Low surfactant production  RDS
Vasoconstriction  poor perfusion  metabolic
acidosis
Delayed transition from fetal to newborn circulation
Thermal shock  DIC  death
Modes of Heat Loss
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Conduction - direct heat transfer from skin to object
(eg mattress)
Convection - heat loss through air flow
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Radiation - direct transfer by electromagnetic radiation
in infrared spectrum
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Also depends on air temp
Heat gained by radiation from external radiant energy source
Heat lost by radiation to cooler walls of incubator
Evaporation - heat loss when water evaporates from
skin and respiratory tract
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Depends on maximum relative humidity of surroundings 
less humidity = more evaporation
Heat Loss at Birth
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Hammarlund et al, 1980
Evaporative H20 loss
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Heat loss through
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81-125 gm/m2/h when unwiped in ambient temp ~25.8deg
C and 42% humidity
Evaporation: 60-80 W/m2
Radiation: 50 W/m2
Convection: 25 W/m2
Conduction: negligible
Total heat loss = 135-155 W/m2
All babies that were >3250g - body temp decreased
0.9deg C in 15min
Heat Loss at Birth
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Hammarlund et al, 1979
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Naked infants <28wks need ambient temp ~40deg
C to maintain nl temp in 20% humidity
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Increasing humidity to 60% halved losses
Attempt to Overcome Losses
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Radiant heaters insufficient to warm preterm
baby
Esp during resuscitation
 750g baby w/ surface area of ~ 0.06m2 requires at
least 9.3W to compensate for losses at birth
 At mattress lvl, max of 9W absorbed by baby if
radiant heat absorbed by, at least, 50% of mattress
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Thermoneutral Environment
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Temp and environmental conditions at which
metabolic rate and O2 consumption are lowest
Silverman et al
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Maintaining constant abdominal skin temp b/w
36.2-36.5 deg C optimal
WHO classification of hypothermia
Mild: 36-36.4deg C
 Mod: 32-35.9deg C
 Severe: <32deg C
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Kangaroo Mother Care (KMC)
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Introduced in 1983 by Rey and Martinez in Colombia
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LBW infants nursed naked (wearing only cloth diaper)
between mothers’ breasts
Data from other countries show infants nursed by KMC have
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Fewer apneic episodes
Similar or better blood oxygenation
Lower infxn rtes
Are alert longer and cry less
Are breastfed longer and have better bonding
Improved survival in low-resource settings
KMC
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Bergman et al, 2004
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Randomized controlled trial comparing KMC to pre-warmed
servo-controlled closed incubator after birth
20 infants b/w 1200-2199g using KMC vs 14 controls
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Excluded if C-sec, mother too ill to look after self/infant, known
HIV, BW outside 1200-2199g, 5min Apgar <6, congenital
malformations
1/20 subjects vs 8/14 controls had initial temps < 35.5deg C
(P = 0.006)
1/20 subjects vs 3/14 controls had bl glucoses < 2.6
mmol/L (though 40mg/dL = 2.2mmol/L)
Stability of cardio-respiratory system in preterm infants
(SCRIP) score was 2.88 points higher w/in 1st 6hrs in KMC
group (95% CI 0.3-5.46)
SCRIP Score
SCRIP
2
1
0
HR
Regular
Decel to 80-100
Rte <80 or
>200 bpm
RR
Regular
Apnea <10s or
periodic
breathing
Apnea >10s or
tachypnea >80
O2 sat
>89%
80-89%
<80%
Barriers to Heat Loss
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Cochrane database review
4 studies compared barriers to heat loss vs. no barriers
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2 comparison subgroups
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Plastic wrap/bag vs routine care
Stockinet cap vs routine care
Plastic wrap/bag vs routine care
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3 studies involving 200 infants all <36wks
All placed under radiant warmer, wrapped to shoulders while
still wet, heads dried and resuscitated according to guidelines
GA <28wks: wrap group had temps 0.76deg C higher than
controls (95% CI 0.49-1.03)
GA 28-31wks: no statistical difference
Barriers to Heat Loss
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Plastic wrap/bag vs routine care (cont)
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1hr after admission for GA <28wks, no statistical difference
(though direction was in favor of intervention)
Plastic wrap significantly reduced risk of hypothermia (core
temp <36.5deg C) on admission to NICU
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RR 0.63 (95% CI 0.42-0.93)
NNT found to be 4 (95% CI 3-17) - so 4 infants would need to be
wrapped in plastic to prevent 1 from becoming hypothermic
No significant differences found in duration of O2 therapy,
major brain injury, duration of hospitalization, or death
Barriers to Heat Loss
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Stockinet cap vs routine care
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1 study involving 40 AGA infants w/ GA’s 32-36wks
Exclusion critera: 5min Apgar <7, SSx CNS defect, sepsis, or
maternal temp >37.8deg C during labor
Cap group had caps placed ASAP after drying under radiant
warmer and infants <2500g were transported in incubator
BW <2000g: Cap group had core temps 0.7deg C higher than
control (95% CI -0.01-1.41) - borderline statistical difference
BW >/= 2000g: no sig dif
No sig dif in preventing hypothermia
External Heat Sources
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Cochrane database review
2 studies compared external heat sources to
routine care
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2 comparison subgroups
Skin-to-skin vs routine care (already mentioned)
 Transwarmer mattress vs routine care
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External Heat Sources
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Brennan et al, 1996
24 infants w/ BW </= 1500g
Transport Mattress (TM) - made of sodium acetate activated to ~40deg C when delivery imminent
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Infant placed upon blankets covering mattress, dried, then
placed on TM directly
Control group = same intervention but w/o TM
Both groups resuscitated according to guidelines then
transferred to NICU on radiant warmer surface
External Heat Sources
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Brennan et al, cont
Increase of 1.6deg C in TM group (95% CI 0.832.37)
Evidence suggests that TM significantly reduces
risk of hypothermia w/ RR 0.3 (95% CI 0.110.83)
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NNT = 2 (95% CI 1-4)
No adverse occurrences reported in this study,
though other studies have had infants sustain
3rd deg burns
In Conclusion
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Plastic barriers effective in reducing heat loss in
newborns <28wks
No evidence yet to suggest plastic barriers decrease
duration of O2 therapy, hospitalization, or incidence of
major brain injury/death
Stockinet caps effective in reducing hypothermia in
newborns <2000g, but not >/= 2000g
KMC shown to be effective in stable newborns down
to 1200g in reducing risk of hypothermia
TM decreases incidence of hypothermia </= 1500g
In the end, the smaller the baby, the more likely any
intervention will be of benefit
Areas of Further Study
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Need more studies w/ larger population bases
Short- and long-term outcomes need to be
studied further (especially w/
neurdevelopmental F/U)
Secondary outcomes that need further study:
Hypoglycemia
RDS
Intubation/ventilation
Length of stay
Metabolic acidosis
ARF
Growth
Adverse events
Neonatal Energy Triangle
References
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Laroia, N. “Double wall versus single wall incubator for reducing heat loss in very low birth
weight infants in incubators.” Cochrane Database of Systematic Reviews. Vol (3) 2007.
Fienady, V. “Radiant warmers versus incubators for regulating body temperature in newborn
infants” Cochrane Database of Systematic Reviews. Vol (3) 2007.
Asakura, H. “Fetal and Neonatal Thermoregulation.” Journal of Nippon Medical School. Vol. 71
(2004) , No. 6.
Ibe, O.E. “A comparison of kangaroo mother care and conventional incubator care for thermal
regulation of infants <200 g in Nigeria using continuous ambulatory temperature monitoring.”
Annals of Tropical Paediatrics (2004) 24, 245-251.
Bergman, N.J. “Randomized controlled trial of skin-to-skin contract from birth versus
conventional incubator for physiological stabilization in 1200- to 2199-gram newborns.” Acta
Paediatrica (2004) 93: 779-785.
McCall, E.M. “Interventions to prevent hypothermia at birth in preterm and/or low birthweight
babies.” Cochrane Database of Systematic Reviews. Vol (3), 2007.
Watkinson, M.A. “Temperature Control of Premature Infants in the Delivery Room.” Clin
Perinaol 33 (2006) 43-53.
“Knobel, R.B. “Heat Loss Prevention for Preterm Infants in the Delivery Room.” J Perinaol 25
(2005) 304-308.
The neonatal energy triangle Part 2: Thermoregulatory and respiratory adaptation.” Paediatric
Nursing. Sept. Vol 18 no 7.
Thank You!!