Temperature Control in the Neonate

1. Temperature Control in the Neonate Pearl S. Park, D.O. PGY-2 August 30, 2007

2. 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

3. 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

4. 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

5. 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)

6. Risk Factors • All neonates in 1st 8-12hrs of life • Prematurity • SGA • CNS problems • Prolonged resuscitation efforts • Sepsis

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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)

15. SCRIP Score

16. 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

17. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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:

25. Neonatal Energy Triangle

26. 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.

27. Thank You!!