An appeal for redesign of ICU ventilators with CO2 absorbers to reduce oxygen usage during a COVID-19 surge

COVID-19 has raised unprecedented issues in the provision of healthcare. Therapy for COVID-19 respiratory disease encompasses various methods of oxygen delivery, with some using flow rates in excess of 100 l.min^-1. Hospitals’ capacity to deliver a consistent oxygen supply has been a major concern, and in certain hospitals supply would have been exceeded without significant changes to the infrastructure [1].

Ventilators designed for critical care have no CO₂ absorbers, and therefore require a fresh gas flow between 2-3 times minute ventilation. Assuming a lung protection strategy, an average adult patient with tidal volume of 350 ml and 10 breaths.min^-1 requires 7-12 l.min^-1 oxygen for sufficient fresh gas flows to eliminate CO₂ rebreathing [2].

Operating theatre anaesthetic machines incorporating CO₂ absorbers require only 1-2 l.min^-1 of oxygen if the ventilator is electronically triggered. Air can also be used as the driving gas, in which case oxygen usage can be reduced 3 to 12-fold compared with an ICU ventilator. This reduction may not be relevant at normal times, but be of considerable benefit during periods of excess oxygen usage within a hospital.

Guidance on the repurposing of anaesthetic machines to act as ICU ventilators has been provided [3], but this is not ideal as the latter have multiple respiratory support modes to cope with the abnormal lung mechanics of critically-ill patients, and ICU staff will not be familiar with the former.

This is an open letter to manufacturers of ventilators, and critical care specialists, to consider designing ICU ventilators with the ability to incorporate a circle system with CO₂ absorption. Innovators might also be able to redesign, repurpose or reengineer this into existing ventilators. We accept that there would be training requirements for nursing staff, as well as the necessity for improved production and supply pathways for CO₂ absorbents.

COVID-19 has highlighted the need to constantly innovate in order to deal with the current crisis as well as future pandemics.

Ian McBride
Specialist Registrar
Stephen Mannion
Consultant
Department of Anaesthesiology, South Infirmary Victoria University Hospital, Cork, Ireland

Twitter: @stephenmannion5

References

1. World Health Organization. Oxygen sources and distribution for COVID-19 treatment centres, Interim guidance, 4/4/2020. https://apps.who.int/iris/bitstream/handle/10665/331746/WHO-2019-nCoV-Oxygen_sources-2020.1-eng.pdf (accessed 29/8/2020).
2. Morgan GE, Mikhail MS, Murray MJ. Clinical Anesthesiology, 3rd edn. New York: Lange Medical Books/McGraw-Hill, 2001.
3. American Society of Anesthesiologists. APSF/ASA guidance on purposing anesthesia machines as ICU ventilators, 7/5/2020. https://www.asahq.org/-/media/files/spotlight/anesthesia-machines-as-icu-ventilators-5-07.pdf (accessed 29/8/2020).