Evaluating the ventilatory effect of transnasal humidified rapid insufflation ventilatory exchange in apnoeic small children with two different oxygen flow rates: a randomised controlled trial*

Transnasal humidified rapid insufflation ventilatory exchange prolongs safe apnoeic oxygenation time in children. In adults, transnasal humidified rapid insufflation ventilatory exchange is reported to have a ventilatory effect with PaCO₂ levels increasing less rapidly than without it. This ventilatory effect has yet to be reproduced in children. In this non-inferiority study, we tested the hypothesis that children weighing 10–15 kg exhibit no difference in carbon dioxide clearance when comparing two different high-flow nasal therapy flow rates during a 10-min apnoea period. Following standardised induction of anaesthesia including neuromuscular blockade, patients were randomly allocated to high-flow nasal therapy of 100% oxygen at 2 or 4 l.kg⁻¹.min⁻¹. Airway patency was ensured by continuous jaw thrust. The study intervention was terminated for safety reasons when SpO₂ values dropped < 95%, or transcutaneous carbon dioxide levels rose > 9.3 kPa, or near-infrared spectroscopy values dropped > 20% from their baseline values, or after an apnoeic period of 10 min. Fifteen patients were included in each group. In the 2 l.kg⁻¹.min⁻¹ group, mean (SD) transcutaneous carbon dioxide increase was 0.46 (0.11) kPa.min⁻¹, while in the 4 l.kg⁻¹.min⁻¹ group it was 0.46 (0.12) kPa.min⁻¹. The upper limit of a one-sided 95%CI for the difference between groups was 0.07 kPa.min⁻¹, lower than the predefined non-inferiority margin of 0.147 kPa.min⁻¹ (p = 0.001). The lower flow rate of 2 l.kg⁻¹.min⁻¹ was non-inferior to 4 l.kg⁻¹.min⁻¹ relative to the transcutaneous carbon dioxide increase. In conclusion, an additional ventilatory effect of either 2 or 4 l.kg⁻¹.min⁻¹ high-flow nasal therapy in apnoeic children weighing 10–15 kg appears to be absent.