Temperature Control in the Neonate

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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 Now considered independent risk factor for mortality in preterm
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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
  • Now considered independent risk factor for mortality in preterm
  • Western philosophy of conventional care – premature baby should be
  • 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
  • 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
  • Metabolic rate of fetus per tissue wt. higher than adult
  • Heat also transferred from mother to fetus via placenta/uterus
  • Fetal temp consistently 0.3-0.5 deg C higher than mother’s (always in parallel)
  • Even when mother’s temp elevates (eg fever)
  • Despite BAT in utero, fetus cannot produce extra heat
  • 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
  • Heat gain/loss controlled by hypothalamus and limbic system
  • Thermoregulatory system immature in newborns (esp premature newborn)
  • In term infant, response to cold stress relies on oxidation of brown fat (NST)
  • 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
  • All neonates in 1st 8-12hrs of life
  • Prematurity
  • SGA
  • CNS problems
  • Prolonged resuscitation efforts
  • Sepsis
  • Adverse Consequences of Hypothermia
  • 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
  • Conduction - direct heat transfer from skin to object (eg mattress)
  • Convection - heat loss through air flow
  • Also depends on air temp
  • Radiation - direct transfer by electromagnetic radiation in infrared spectrum
  • 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
  • Depends on maximum relative humidity of surroundings  less humidity = more evaporation
  • Heat Loss at Birth
  • Hammarlund et al, 1980
  • Evaporative H20 loss
  • 81-125 gm/m2/h when unwiped in ambient temp ~25.8deg C and 42% humidity
  • Heat loss through
  • 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
  • Hammarlund et al, 1979
  • Naked infants <28wks need ambient temp ~40deg C to maintain nl temp in 20% humidity
  • Increasing humidity to 60% halved losses
  • Attempt to Overcome Losses
  • 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
  • Thermoneutral Environment
  • Temp and environmental conditions at which metabolic rate and O2 consumption are lowest
  • Silverman et al
  • 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
  • Kangaroo Mother Care (KMC)
  • Introduced in 1983 by Rey and Martinez in Colombia
  • LBW infants nursed naked (wearing only cloth diaper) between mothers’ breasts
  • Data from other countries show infants nursed by KMC have
  • 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
  • Bergman et al, 2004
  • 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
  • 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 Barriers to Heat Loss
  • Cochrane database review
  • 4 studies compared barriers to heat loss vs. no barriers
  • 2 comparison subgroups
  • Plastic wrap/bag vs routine care
  • Stockinet cap vs routine care
  • Plastic wrap/bag vs routine care
  • 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
  • Plastic wrap/bag vs routine care (cont)
  • 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
  • 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
  • Stockinet cap vs routine care
  • 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
  • Cochrane database review
  • 2 studies compared external heat sources to routine care
  • 2 comparison subgroups
  • Skin-to-skin vs routine care (already mentioned)
  • Transwarmer mattress vs routine care
  • External Heat Sources
  • Brennan et al, 1996
  • 24 infants w/ BW </= 1500g
  • Transport Mattress (TM) - made of sodium acetate - activated to ~40deg C when delivery imminent
  • 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
  • Brennan et al, cont
  • Increase of 1.6deg C in TM group (95% CI 0.83-2.37)
  • Evidence suggests that TM significantly reduces risk of hypothermia w/ RR 0.3 (95% CI 0.11-0.83)
  • 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
  • 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
  • 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:
  • Neonatal Energy Triangle References
  • 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.
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