Neonatal hypothermia and thermoregulation — formative SAQs

SAQ 1 — The cold preterm on admission (10 marks)

A 28-week gestation, 950 g infant is delivered by emergency caesarean for preterm labour. The delivery room was noted to be cool. The infant arrives in the neonatal unit 15 minutes after birth, wrapped in a towel that is damp. The axillary temperature is 35.0 C, the infant is pale and grunting, and the bedside glucose is 1.6 mmol/L. [9]

a) Classify this infant's temperature by the WHO band and state the target normothermic range. (2 marks) [9]

The axillary temperature of 35.0 C places this infant in the moderate hypothermia band (32.0–35.9 C). The target normothermic range is 36.5–37.5 C. Moderate hypothermia is the band in which admission hypothermia in preterm infants most commonly sits, and in very preterm infants it is independently associated with mortality and major morbidity. [9]

b) List the four physical pathways of heat loss and state which dominates at birth and why. (3 marks) [1]

The four pathways are evaporation (water converting to vapour from the wet skin), radiation (heat radiating from the skin to cooler surrounding walls), convection (moving air carrying heat away — drafts, transport), and conduction (heat lost to a cold surface in direct contact — scales, cold towels, a cold mattress). Evaporation dominates at birth because the infant is wet with amniotic fluid and the skin-to-air gradient is large; this is why immediate drying is the single highest-yield warm-chain step. [1]

c) Describe your immediate management of this infant, including the rewarming strategy and the metabolic priority. (3 marks) [9]

The management is active external rewarming: place the infant under a pre-warmed radiant warmer or in a servo-controlled incubator, remove the damp towel, apply a hat, and monitor continuously, targeting a rewarming rate of roughly 0.5 C per hour. The metabolic priority is to correct the hypoglycaemia — give a bolus of 10% dextrose (typically 2 mL/kg) followed by a continuous dextrose infusion — because thermogenesis consumes glucose and hypoglycaemia disables thermogenesis. Watch for apnoea during rewarming. [9]

d) State the delivery-room interventions that would have prevented this, citing the evidence base for the very preterm. (2 marks) [3]

A warm delivery room (above 25 C), immediate drying and a change to a dry towel, a hat, and — specifically for the very preterm (under 32 weeks) — plastic wrap without drying under a radiant warmer. The Cochrane review of interventions to prevent hypothermia at birth in preterm infants found that plastic wraps reduce hypothermia, and the JAMA Pediatrics network meta-analysis ranked the combination of plastic bag, cap and radiant warmer as the highest delivery-room strategy. [3] [4]