Background. Transnasal humidified rapid-insufflation ventilatory exchange (THRIVE) was introduced to adult anaesthesia to improve the safety of airway management during apnoea before intubation. The objective of our study was to determine whether THRIVE safely prolongs apnoeic oxygenation in children. Methods. This was a randomized controlled trial in 48 healthy children, with normal airways and cardiorespiratory function, in age groups 0–6 and 7–24 months, 2–5 and 6–10 yr old, presenting for elective surgery or imaging under general anaesthesia. All children were induced with sevoflurane, O2, and N2O, followed by muscle relaxation with rocuronium, and standardized preoxygenation with bag-and-mask ventilation. The control arm received jaw support during apnoea, whereas the THRIVE arm received jaw support during apnoea and age-specific flow rates. The primary outcome was to demonstrate that children allocated to THRIVE maintain transcutaneous haemoglobin saturation at least twice as long as the expected age-dependent apnoea time in the control group. Results. Both study arms (each n=24) were similar in age and weight. The apnoea time was significantly shorter in the control arm: average 109.2 (95% CI 28.8) s in the control arm and 192 s in the THRIVE arm (0–6 months), 147.3 (95% CI 18.9) and 237 s (7–24 months), 190.5 (95% CI 15.3) and 320 s (2–5 yr), and 260.8 (95% CI 37.5) and 430 s (6–10 yr), respectively. Average transcutaneous haemoglobin saturation remained at 99.6% (95% CI 0.2) during THRIVE. Transcutaneous CO2 increased to a similar extent in both arms, with 2.4 (95% CI 0.5) mm Hg min−1 for the control arm and 2.4 (95% CI 0.4) mm Hg min−1 for the THRIVE arm. Conclusion. Transnasal humidified rapid-insufflation ventilatory exchange prolongs the safe apnoea time in healthy children but has no effect to improve CO2 clearance.