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

Background Adjusting the fraction of inspired oxygen (FiO 2) delivered to preterm infants to keep their oxygen saturation within target range remains challenging. Closed-loop automated FiO 2 control increases the time infants spend within the assigned target range. The delay with which FiO 2 adjustments at the ventilator result in a change in the inspired gas limits the performance of both manual and automated controls. Objective To evaluate the equilibration time (T eq) between FiO 2 adjustments and changes in FiO 2 reaching the patient. Methods In vitro determination of the delay in FiO 2 adjustments at the ventilator at 5 and 8 L/min of gas flow and two different humidifier/ventilator circuit volumes (840 and 432 mL). Results T eq 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. Conclusion The identified delay seems clinically relevant and should be taken into account during manual and automatic control of FiO 2.