Neonatal hypothermia and thermoregulation

Overview & Definition

A 28-week infant arrives in the neonatal unit at 35.2 C, pale and grunting, with a glucose of 1.6 mmol/L. You have minutes to correct both. Neonatal hypothermia is defined by the World Health Organization as an axillary temperature below 36.5 C in a baby from birth to 28 days, with cold stress beginning moment temperature dips below 36.5 C and graded by severity into mild, moderate, and severe bands. ^[8] It is not a trivial number on a chart — it is a marker of how well the delivery-room and early-neonatal system is protecting a vulnerable infant, and it is the single most preventable cause of early neonatal morbidity. ^{[3] [10]}

The newborn is a thermoregulatory outlier. Compared with an older infant or adult, it has a high surface-area-to-mass ratio (the preterm is the extreme), a thin, permeable skin that is wet with amniotic fluid at birth, a finite brown-fat and glycogen store, and a thermogenic machinery that relies on non-shivering thermogenesis because shivering is poorly developed before term. ^[1] The infant can generate heat, but only through oxidation of brown adipose tissue, and only while its glycogen and oxygen supply last. When the environment overwhelms that capacity, the temperature falls and the metabolic cascade of cold injury begins. ^[9]

The clinical importance of the topic rests on three facts every fellowship candidate must hold together. First, hypothermia is common — in well-resourced settings admission hypothermia affects a large fraction of very preterm infants despite protocols, and in low-resource settings the prevalence at admission routinely exceeds half of all newborns. ^[8] Second, it is harmful — admission hypothermia in very preterm infants is independently associated with late-onset sepsis, intraventricular haemorrhage, necrotising enterocolitis, bronchopulmonary dysplasia, and death, with a dose-response gradient across the temperature bands. ^[9] Third, and decisively, it is preventable — a bundled sequence of simple, low-cost interventions called the warm chain, applied from the moment of birth, prevents most cases and is among the most evidence-supported bundles in neonatology. ^{[3] [10]}

The modern story of this topic is one of prevention and protocol, not of dramatic rescue. The golden-hour concept, the plastic wrap for the very preterm, the servo-controlled incubator, and kangaroo mother care have together transformed thermal care from an afterthought into a measurable quality metric — the admission temperature of the preterm infant is now tracked and benchmarked in every neonatal network, and the warm chain is taught as a non-negotiable. ^{[10] [11]}

References12ShowHide

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