KEY TAKEAWAYS
- Newborns lose heat fast — high surface-area-to-mass ratio, thin skin, little insulation, and an inability to shiver mean they rely on non-shivering thermogenesis (brown fat), which consumes glucose and oxygen.
- Normal axillary temperature is 36.5–37.5°C; WHO grades hypothermia as mild/cold stress (36.0–36.4), moderate (32.0–35.9), and severe (<32°C).
- Cold stress is dangerous, not trivial — it drives hypoglycemia, hypoxia, metabolic acidosis, PPHN, respiratory distress, coagulopathy, and is an independent risk factor for mortality.
- Heat is lost four ways — evaporation, conduction, convection, radiation — and the delivery room attacks on all four.
- Prevention wins: warm room, immediate drying (term) or polyethylene wrap without drying (preterm <32 weeks), hat, exothermic mattress, radiant warmer, and heated humidified gases.
- New-onset hypothermia can signal sepsis — look for a cause, and rewarm carefully.
1. Clinical Overview
Clinical Overview
Temperature control is a survival skill the newborn has only partly developed. Compared with adults, neonates have a large surface area relative to body mass, thin skin, minimal subcutaneous fat, and no ability to shiver, so they defend their temperature mainly through non-shivering thermogenesis — metabolizing brown adipose tissue — a process that is metabolically expensive, burning glucose and oxygen. The preterm infant is even more vulnerable (less brown fat, thinner skin, higher surface-area ratio, immature skin barrier). When heat loss outpaces production, cold stress ensues, triggering a damaging cascade: hypoglycemia, increased oxygen consumption, acidosis, pulmonary vasoconstriction, and respiratory compromise. Because hypothermia independently increases neonatal mortality, the delivery-room "golden hour" prioritizes preventing heat loss — and the clinician must also remember that an unexpectedly cold baby may be septic.
2. Definitions
| Term | Meaning |
|---|
| Normothermia | Axillary temperature 36.5–37.5°C. |
| Cold stress / mild hypothermia | 36.0–36.4°C (WHO). |
| Moderate hypothermia | 32.0–35.9°C. |
| Severe hypothermia | <32°C. |
| Non-shivering thermogenesis | Heat production by metabolizing brown fat (neonates can't shiver). |
| Neutral thermal environment (NTE) | Ambient temperature at which the infant maintains normal body temperature with minimal metabolic/oxygen cost. |
3. Pathophysiology
Pathophysiology
Why newborns lose heat: large surface-area-to-mass ratio, thin skin with little insulating fat, immature epidermal barrier (preterm), and inability to shiver.
The four routes of heat loss:
- Evaporation — from wet skin (amniotic fluid) and the respiratory tract (biggest early loss; addressed by drying/wrapping and humidified gases).
- Conduction — to cold surfaces in contact (cold scales, blankets, hands).
- Convection — to moving cool air (drafts, cold delivery room).
- Radiation — to nearby cold surfaces (cold walls/windows, even without contact).
Heat defense: non-shivering thermogenesis metabolizes brown fat (norepinephrine- and thyroid-mediated), consuming glucose and oxygen — which is why cold stress produces hypoglycemia and increased oxygen demand.
4. Consequences of Cold Stress
Consequences of Cold Stress
- Metabolic: hypoglycemia (glucose consumed for heat), metabolic acidosis (anaerobic metabolism/lactate), increased oxygen consumption.
- Respiratory/cardiac: pulmonary vasoconstriction → PPHN, hypoxia, respiratory distress, surfactant impairment.
- Hematologic: coagulopathy, and (chronically) poor weight gain.
- Associations: increased IVH, late-onset sepsis, pulmonary hemorrhage, and mortality (hypothermia is an independent risk factor).
5. Risk Factors
Risk Factors
Prematurity/low birth weight (dominant), IUGR/SGA, delivery-room exposure, resuscitation/procedures, hypoxia/asphyxia, sepsis, CNS abnormalities, and a cold environment (transport, low room temperature).
6. Prevention — the delivery-room "golden hour"
Prevention — the delivery-room "golden hour"
- Warm the birthing environment (≥~23–25°C).
- Term/stable infant: dry immediately, remove wet linens, and provide skin-to-skin contact (with a hat).
- Preterm (<32 weeks): place in a polyethylene plastic wrap/bag WITHOUT drying, add a hat/cap, use an exothermic warming mattress and a radiant warmer, and provide heated, humidified respiratory gases. (Plastic wrap significantly reduces hypothermia; watch for hyperthermia and remove when normothermic.)
- Humidified incubator for preterm infants (also reduces insensible water loss).
- Maintain warmth during delayed cord clamping, transport, and procedures.
- Servo-controlled warmer/incubator to target skin/core temperature.
7. Management of the Hypothermic Infant
Management of the Hypothermic Infant
- Rewarm using a radiant warmer or (servo-controlled) incubator; the optimal rate is debated — avoid rapid rewarming (associated with apnea and hypotension). Monitor closely.
- Check and treat glucose (hypoglycemia is common), acid-base, and vital signs.
- Look for a cause — especially sepsis (hypothermia can be a presenting sign), as well as environmental exposure and CNS causes.
- Support cardiorespiratory status; address PPHN/respiratory distress if present.
Do not confuse accidental hypothermia with therapeutic hypothermia for HIE — the latter is a deliberate, protocolized treatment (see the HIE chapter), not to be replicated by allowing cold stress.
8. Hyperthermia (brief)
Hyperthermia (brief)
- Distinguish overheating (environmental/iatrogenic — over-wrapping, warmer set too high) from fever (infection).
- Dehydration can raise temperature.
- Address the cause; adjust the environment; evaluate for infection when appropriate.
9. Monitoring
Monitoring
- Continuous or frequent temperature monitoring (axillary/skin/servo).
- Glucose, acid-base, vital signs during cold stress and rewarming.
- Environmental parameters (warmer/incubator settings, humidity, room temperature).
- Sepsis evaluation when hypothermia is unexplained.
10. Complications
Complications
- Hypoglycemia, metabolic acidosis, hypoxia, PPHN, respiratory distress, coagulopathy.
- Increased IVH, late-onset sepsis, pulmonary hemorrhage.
- Increased mortality (independent risk factor).
- From rewarming: apnea, hypotension if too rapid.
- From overheating: hyperthermia, dehydration.
11. Safety Warnings
Safety Warnings
- ⚠️ Cold stress is dangerous — it causes hypoglycemia, acidosis, PPHN, and raises mortality.
- ⚠️ Prevent heat loss in the delivery room — warm room, dry (term) or wrap without drying (preterm), hat, mattress, warmer, humidified gases.
- ⚠️ A cold baby may be septic — evaluate for infection.
- ⚠️ Rewarm carefully — rapid rewarming can cause apnea/hypotension.
- ⚠️ Watch for hyperthermia with plastic wrap/warmers — remove/adjust when normothermic.
- ⚠️ Check glucose in any cold-stressed infant.
12. Common Mistakes
Common Mistakes
- Underestimating cold stress as benign.
- Drying a very preterm infant instead of using a plastic wrap (drying increases evaporative loss in this group).
- Rewarming too rapidly (apnea/hypotension).
- Missing sepsis as a cause of hypothermia.
- Forgetting to check glucose.
- Overheating with warmers/wraps (hyperthermia).
- Neglecting warmth during transport and procedures.
13. Clinical Pearls
Clinical Pearls
- 💡 Brown fat costs sugar and oxygen — cold stress → hypoglycemia and hypoxia.
- 💡 Four routes of loss — evaporation, conduction, convection, radiation — attack all four.
- 💡 Preterm: wrap, don't dry — plastic beats a towel for the tiniest.
- 💡 A cold baby is a septic baby until proven otherwise.
- 💡 Rewarm slowly and watch — fast rewarming has its own hazards.
- 💡 Accidental cold ≠ therapeutic cooling — don't conflate them.
14. Summary Table
Summary Table
| Domain | Bottom line |
|---|
| Normal temp | 36.5–37.5°C axillary |
| WHO hypothermia | Mild 36.0–36.4 · moderate 32.0–35.9 · severe <32°C |
| Why vulnerable | High SA:mass, thin skin, little fat, no shivering → brown-fat thermogenesis (uses glucose/O₂) |
| Heat loss | Evaporation, conduction, convection, radiation |
| Consequences | Hypoglycemia, acidosis, PPHN, respiratory distress, coagulopathy, ↑mortality |
| Prevent | Warm room; dry (term)/wrap without drying (preterm); hat; exothermic mattress; warmer; humidified gases |
| Rewarm | Carefully (avoid rapid); check glucose/acid-base; evaluate for sepsis |
| Don't confuse | Accidental hypothermia ≠ therapeutic hypothermia for HIE |
15. Step-by-Step Bedside Algorithm
DELIVERY ROOM (prevention / golden hour)
• warm room (≥23–25°C)
• TERM/stable → dry immediately + remove wet linens + skin-to-skin + hat
• PRETERM <32 wk → POLYETHYLENE WRAP WITHOUT DRYING + hat + exothermic mattress
+ radiant warmer + heated humidified gases
• keep warm during delayed cord clamping, transport, procedures
│
▼
MEASURE TEMPERATURE (axillary 36.5–37.5°C target)
│
HYPOTHERMIC?
├─ Yes → REWARM (radiant warmer/incubator; avoid RAPID rewarming)
│ + CHECK GLUCOSE + acid-base + vitals
│ + EVALUATE FOR SEPSIS (and other causes)
│ + support cardiorespiratory status (watch PPHN)
│
└─ Hyperthermic? → distinguish overheating (adjust environment) vs FEVER (evaluate infection);
check hydration
│
▼
Ongoing: temperature monitoring (servo), maintain neutral thermal environment,
watch for hyperthermia with wrap/warmer (remove when normothermic)
[Accidental hypothermia is NOT therapeutic hypothermia — see HIE chapter]
16. References to Verify
Confirm each against the primary source before clinical or published use.
- 1.WHO: Thermal Protection of the Newborn: A Practical Guide — hypothermia classification and prevention. (Verify grades/targets.)
- 2.Delivery-room guidance: NRP/ILCOR thermoregulation recommendations (warm room, polyethylene wrap, exothermic mattress, humidified gases). (Verify.)
- 3.Plastic wrap: systematic reviews/meta-analyses of polyethylene wrap reducing hypothermia in preterm infants (with a hyperthermia signal). (Verify.)
- 4.Outcomes: evidence that hypothermia is an independent risk factor for neonatal mortality/morbidity. (Verify.)
- 5.HIE distinction: therapeutic hypothermia references (see the HIE chapter) — to contrast with accidental cold stress. (Verify.)