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In vitro evaluation of delays in the adjustment of the fraction of inspired oxygen during CPAP: effect of flow and volume
  1. Christoph E. Schwarz1,2,3,
  2. Gordon Lightbody3,4,
  3. Ingo Müller-Hansen1,
  4. Jörg Arand1,
  5. Christian F. Poets1,
  6. Axel R. Franz1,5
  1. 1 Department of Neonatology, University Children’s Hospital, Tübingen, Germany
  2. 2 Department of Paediatrics and Child Health, University College Cork, Cork, Ireland
  3. 3 INFANT Research Centre, University College Cork, Cork, Ireland
  4. 4 Department of Electrical and Electronic Engineering, University College Cork, Cork, Ireland
  5. 5 Center for Pediatric Clinical Studies, Universitätsklinikum Tübingen, Tubingen, Baden-Württemberg, Germany
  1. Correspondence to Dr Christoph E. Schwarz, Department of Neonatology, University Children’s Hospital, 72076 Tübingen, Germany; C.Schwarz{at}


Background 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.

Objective To evaluate the equilibration time (Teq) between FiO2 adjustments and changes in FiO2 reaching the patient.

Methods 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).

Results 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.

Conclusion The identified delay seems clinically relevant and should be taken into account during manual and automatic control of FiO2.

  • neonatology
  • technology
  • clinical procedures
  • physiology
  • respiratory

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  • Contributors CES conceived the study, performed measurements, participated in the analysis, wrote the first draft and the revised the draft of the manuscript. GL analysed the measurements, performed the data analysis and contributed to the first draft and the revised draft of the manuscript. IM-H and JA participated in study design and measurements and critically reviewed the manuscript. CFP critically reviewed the manuscript. AF contributed to the design of the study, participated in analysis and critically reviewed the manuscript. All authors read and approved the final manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests CES, CFP and AF were supported by both Löwenstein Medical and Fritz Stephan GmbH for different research projects. The University of Tübingen holds a patent on the closed-loop automated control (CLAC) algorithm for automated oxygen control and has a licencing agreement with Löwenstein Medical in relation to this algorithm. AF and CFP are supported by a grant of the German Ministry of Research and Education for conducting an FiO2-controller study on the medium-term effects of CLAC of FiO2.

  • Patient consent for publication Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement Data are available upon reasonable request. Contact the corresponding author.

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