A term neonate born in an unheated delivery room becomes lethargic with a rectal temperature of 35.2 degrees C. The principal mechanism by which this neonate generates heat is:

• A Shivering of skeletal muscle mediated by the hypothalamus
• B Increased voluntary muscular activity and crying
• C Non-shivering thermogenesis in brown adipose tissue via uncoupling protein 1 ✓
• D Cutaneous vasoconstriction reducing heat loss

Explanation

Neonates have negligible shivering capacity and rely on non-shivering thermogenesis. Brown fat, concentrated in the interscapular region, expresses uncoupling protein 1 (thermogenin), which dissipates the mitochondrial proton gradient as heat under sympathetic norepinephrine drive. Vasoconstriction conserves heat but generates none, so it cannot correct hypothermia. Cold stress also raises oxygen consumption, which worsens distress in a compromised neonate.

Reference: Nelson Textbook of Pediatrics, 21st ed.

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