In vitro evaluation of delays in the adjustment of the fraction of inspired oxygen during CPAP: effect of flow and volume.

<bold>Background: </bold>Adjusting the fraction of inspired oxygen (FiO2) delivered to preterm infants to keep their oxygen saturation within target range remains challenging. Closed-loop automated FiO2 control increases the time infants spend within the assigned target range. The delay with which FiO2 adjustments at the ventilator result in a change in the inspired gas limits the performance of both manual and automated controls.<bold>Objective: </bold>To evaluate the equilibration time (Teq) between FiO2 adjustments and changes in FiO2 reaching the patient.<bold>Methods: </bold>In vitro determination of the delay in FiO2 adjustments at the ventilator at 5 and 8 L/min of gas flow and two different humidifier/ventilator circuit volumes (840 and 432 mL).<bold>Results: </bold>Teq values were 31, 23, 20 and 17 s for the volume-flow combinations 840 mL+5 L/min, 840 mL+8 L/min, 432 mL+5 L/min and 432 mL+8 L/min, respectively.<bold>Conclusion: </bold>The identified delay seems clinically relevant and should be taken into account during manual and automatic control of FiO2. [ABSTRACT FROM AUTHOR]