Background: Thermal homeostasis remains a fundamental aspect of neonatal intensive care, yet modern practice differs significantly from earlier studies. Contemporary cohorts include infants at the edge of viability, characterised by immature skin, limited thermogenic capacity, and extended ventilatory support. Simultaneously, incubator design has evolved from basic normothermic chambers to servo-controlled, high-humidity environments. Additionally, infants often require weeks of support with heated respiratory circuits. These developments introduce complex, interacting thermal inputs that were not present in earlier physiology, yet current protocols remain largely empirical. Summary: Evaporative heat loss, caused by transepidermal water loss (TEWL), mainly influences the thermal balance of very preterm infants. TEWL can be equal to or greater than metabolic heat production, especially in the early postnatal period. Its factors include gestation, vapour pressure gradients, and environmental dew point. High relative humidity lessens evaporative stress but reduces the safety margin, raising the risk of condensation and subsequent cooling. Additional instability comes from convective and conductive losses during handling, as well as the thermal effects of ventilator circuits. Key Messages: We suggest reframing neonatal thermal care as actively managing thermal and vapour gradients, rather than only maintaining core normothermia. Evidence-based strategies include keeping high relative humidity soon after birth, minimising isolette openings, pre-warming contact surfaces, and recognising dew point thresholds. Research priorities involve defining optimal humidity protocols, measuring circuit thermal load, and validating monitoring systems that combine oxygen consumption with environmental factors. Tackling these gaps may reduce metabolic stress, enhance survival, and optimise outcomes for the most vulnerable infants.
Andersen et al. (Thu,) studied this question.