11.1 Thermoregulation in the Preterm Newborn

Why Thermoregulation Dominates Preterm Resuscitation

When you open the NRP lesson on infants born preterm, thermoregulation is not a side note after airway and breathing—it is a primary survival skill. A very preterm newborn can lose heat so fast that core temperature falls during the Golden Minute even when the team performs perfect bag-mask technique. Cold stress raises oxygen consumption, worsens metabolic acidosis, increases pulmonary vascular resistance, impairs surfactant function, and is associated with higher rates of mortality and major morbidity. On knowledge checks and in simulation, teams that “get the airway right” but leave the baby uncovered on a cool mattress still fail the scenario’s quality targets.

This section focuses on why preterm infants get cold, how NRP-style thermal protection differs from term initial steps, and how to avoid the opposite error—overheating under aggressive warming. Respiratory support for preterm infants and team readiness for preterm birth follow in the next sections.

Why Preterm Infants Lose Heat Faster Than Term Infants

Heat loss after birth occurs by evaporation (wet skin), convection (moving cool air), conduction (cold surfaces), and radiation (cooler surrounding walls and equipment). Preterm anatomy multiplies each pathway:

A vigorous term infant can often be dried thoroughly, placed skin-to-skin, and maintain temperature with maternal warmth and a hat. A 26-week infant cannot rely on that same pathway. Expect exaggerated heat loss the moment the infant is exposed, and plan thermal protection before delivery rather than as a rescue after the first cold reading.

Target: Normothermia—Not “Warm Enough to Touch”

NRP and neonatal quality programs aim for normal temperature after birth and on NICU admission—commonly discussed in the range of about 36.5–37.5 °C axillary/core targets used in many units (know your local policy and device site). Two failure modes matter equally:

1. Hypothermia — associated with increased mortality, respiratory distress, hypoglycemia, and other morbidities in observational and quality-improvement literature.
2. Iatrogenic hyperthermia — overheating under radiant warmers, heated mattresses, plastic wraps, and warmers used without monitoring can also harm the infant.

Temperature is both a process measure (did the team protect heat?) and an outcome modifier (cold babies do worse). Treat admission temperature as a quality metric your team owns, not as a random NICU lab value.

Plastic Wrap or Bag: The Preterm Thermal Exception

For very preterm newborns, standard vigorous towel drying is often not the first thermal move. Instead, NRP-oriented practice emphasizes:

• Place the infant immediately under a radiant warmer
• Cover the body in a polyethylene plastic wrap or bag, typically covering the trunk and extremities while leaving the head accessible for airway management
• Often without routine towel drying of the body, because drying delays enclosure and evaporative loss continues while the infant is rubbed
• Gently dry or manage the head as needed and place a hat
• Proceed with airway positioning, stimulation as appropriate, and ventilation while the wrap remains in place

The plastic reduces evaporative heat loss by trapping a humid microenvironment against the skin. You can still assess color, chest movement, and lines/cords through or around the wrap with practice. Do not interpret “plastic wrap” as “ignore the airway.” Thermal protection and airway management happen together.

Who is “very preterm” in practice language?

Exact gestational-age cutoffs and local protocols vary by unit and by the edition of guidance your course materials follow. Conceptually for NRP exams and simulation:

• Very preterm / extremely preterm infants are the classic plastic-wrap candidates.
• Moderately preterm infants may use a mix of drying, warm blankets, and warmer care per local protocol.
• Always follow current NRP course content and institutional policy for the gestational-age threshold used on your unit.

If a scenario states “24-week infant just delivered,” expect plastic + radiant warmer + hat, not a prolonged open-air drying sequence.

Radiant Warmer, Room Temperature, and the Delivery Environment

Thermal protection is a system, not a single product:

Radiant warmer

• Pre-warm the bed before birth when preterm delivery is anticipated.
• Place the infant on the warmer surface promptly after the cord management plan and rapid evaluation route the baby away from routine maternal care.
• Use servo-control temperature probes when available and when your protocol supports them during prolonged resuscitation—do not leave a high manual heat setting unattended for long periods.

Warm delivery room

• Increase room temperature for expected preterm births (many QI bundles target a warmer room than a typical adult OR).
• Close doors, limit drafts from HVAC vents over the warmer, and minimize wet linen left under the infant.

Hat and coverings

• The head is a large heat-loss surface in newborns. A hat after (or with) plastic wrap is standard.
• Avoid leaving the infant fully exposed for procedures that can wait; cluster interventions under the warmer.

Heated mattresses and adjuncts

• Some units add chemical mattresses or other heat sources for extremely low birth weight infants. Know that more heat devices without monitoring raise hyperthermia risk. Adjuncts never replace plastic wrap + radiant warmer as core concepts on NRP assessments.

Continuous Temperature Monitoring

You cannot manage what you do not measure. During prolonged resuscitation and before NICU transfer:

• Obtain a temperature as soon as practical without delaying life-saving ventilation.
• Reassess temperature when interventions change (wrap removed for procedures, prolonged open chest exposure, transport).
• Document admission temperature—it is often tracked for hospital quality dashboards.

If heart rate and saturation improve but temperature is 34.8 °C on arrival to the NICU, the resuscitation is incomplete from a systems perspective. Conversely, if the warmer was maxed for 20 minutes under plastic and temperature is 38.2 °C, you have created a new problem. Titrate heat like you titrate oxygen.

Integrating Thermoregulation With the Algorithm

Preterm thermal care inserts into the familiar sequence:

1. Anticipate preterm birth → warm room, preheat warmer, open plastic wrap, hat ready.
2. After birth → initiate cord management plan (when feasible and per plan; see special considerations).
3. Rapid evaluation often yields “preterm” → move to warmer.
4. Thermal strategy (plastic wrap/bag for very preterm; dry/warm for others per protocol) runs in parallel with positioning, stimulation, and airway clearance if needed.
5. Apply monitors; start PPV/CPAP/oxygen as indicated while keeping the wrap in place.
6. Maintain temperature through procedures, lines, and transfer to NICU.

Do not remove the wrap for a casual full exam mid-code. Do not place cold stethoscopes and wet blankets on the chest as a routine. Do not park the infant on an unheated scale “for a quick weight” before thermal stability.

Common Failure Modes (Exam and Bedside)

Scenario Walk-Throughs

Scenario A. Twin A at 27 weeks is born limp. The team places the infant in a polyethylene bag under a radiant warmer without prolonged drying, positions the airway, and starts PPV for apnea while a hat is applied. Temperature probe is placed when feasible. → Correct integrated preterm approach.

Scenario B. A 29-week infant is dried thoroughly with multiple towels on an unheated bed in a cold OR, then moved to the warmer after two minutes. Admission temperature is hypothermic despite “good PPV.” → Thermal system failure.

Scenario C. Extremely preterm infant under plastic and high radiant heat for 25 minutes; axillary temperature 38.4 °C. → Iatrogenic hyperthermia—reduce heat source, recheck, continue supportive care.

Exam Mindset Checklist

• Name the anatomic reasons preterm infants get cold (thin skin, surface area, low fat, immaturity).
• Associate very preterm with plastic wrap/bag ± without drying + radiant warmer + hat.
• Call temperature a quality metric and outcome modifier.
• Avoid both hypothermia and hyperthermia.
• Protect heat during NICU transfer, not only during the first minute.

If you remember one sentence: for the very preterm infant, stop evaporative loss with plastic under a radiant warmer while you open the lungs—and measure temperature so you neither under-warm nor over-warm.