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Abstract

There are instances where hospitals may experience a relative shortage of oxygen, for example, future pandemics, natural disasters or wartime. We developed a modification to a domiciliary ventilator that captures oxygen normally vented during expiration into the atmosphere, delivering it to the patient. The modification significantly increases PaO₂ in mechanically ventilated patients at their baseline FiO₂ and baseline FiO₂ +1, +2 and +3 L/min compared to no modification. The modification reduces walled oxygen consumption by median (IQR) −1.0 (−1.25 to −1.00) L/min whilst maintaining PaO₂. This modification may be a valuable in circumstances where there is a relative shortage of oxygen.

Keywords

Respiration artificial critical care ventilators mechanical oxygen

Introduction

Healthcare institutions can experience a relative shortage of oxygen if there is high demand or a shortage of supply. During the COVID pandemic there were numerous instances of hospitals running out of oxygen due to high demand.^1
–4 Similarly, in poorly resourced healthcare systems or during natural disasters or wartime, oxygen may be in short supply.

Domiciliary ventilators were frequently used during the pandemic due to a shortage of ICU ventilators. In 2020 we showed, in vitro, that a simple modification to a domiciliary ventilator could capture oxygen normally vented into the atmosphere during expiration to increase FiO₂ delivered by the ventilator.⁵ Here we tested this modification in vivo in critically ill, mechanically ventilated patients.

Methods

The study was approved by the Wales research ethics committee 6 (Reference 212/WA/0264) on 11 October 2022. To capture oxygen vented into the atmosphere during the expiratory phase we machined an adaptor from medical grade acetal plastic (POM C, Ensinger, Germany). This was attached to the air inlet (which, as with many other ventilators also acts as an oxygen exhaust) on a Breas Nippy 4+ (Breas Medical, Sweden) domiciliary ventilator. A T-piece connector, bacterial filter and reservoir bag were fitted to form the modification (Figure 1), which in the expiratory phase, captures oxygen usually vented into the atmosphere into the reservoir bag. During inhalation, the oxygen rich gas captured in the reservoir bag mixes with the constant oxygen supply, providing a higher oxygen concentration gas mixture to the patient.

Figure 1.

Breas Nippy 4+ ventilator with modification fitted.

Participants were switched to the Breas Nippy 4+ for the study. Entrained oxygen (L/min) was adjusted to match the FiO₂ delivered on their ICU ventilator. After 10 min FiO₂, PaO₂ and PaCO₂ were measured. The modification was then fitted to the ventilator; after 10 min FiO₂, PaO₂ and PaCO₂ were measured. This process was repeated after increasing oxygen delivered to the ventilator by 1, 2 and 3 L/min compared to baseline with the modification fitted (or not) in random order (Sealed Envelope, Oxford, UK). The modification was then fitted to the ventilator to conserve oxygen; entrained oxygen delivered to the ventilator was reduced to maintain baseline FiO₂; after 10 min FiO₂, PaO₂ and PaCO₂ were measured.

Comparison of variables with and without the modification were analysed using the Wilcoxon signed rank test using SPSS v29.0.1.0 (IBM, Chicago, USA).

Results

Ten patients consented to the study; all were receiving spontaneous ventilation (continuous positive airway pressure ± pressure support) via tracheostomy. Baseline characteristics: median (IQR) age 66.5 (60.2–78.2) years; BMI 28.5 (25.1–30.6); Length of mechanical ventilation 13.5 (7.3–28.3) days; FiO₂ baseline 0.30 (0.29–0.34); Sequential Organ Failure Assessment score 7.0 (5.75–8.25).

The modification fitted to the ventilator significantly increased PaO₂ at baseline FiO₂, and with 1, 2 and 3 L/min additional oxygen entrained by a median (IQR) of 1.63 (1.35–2.17) kPa, 1.60 (0.87–2.80) kPa, 2.15 (3.02–8.42) kPa and 3.65 (2.47–4.57) kPa respectively compared to no modification, without significantly affecting PaCO₂ (Table 1).

Table 1.

PaO₂ FiO₂ and PaCO₂ with no modification and with modification attached.

Walled oxygen increase from baseline (L/min)	PaO₂ (kPa) no modification	PaO₂ (kPa) modification attached	PaO₂ change p-value	FiO₂ no modification	FiO₂ modification attached	FiO₂ change p-value	PaCO₂ (kPa) no modification	PaCO₂ (kPa) modification attached	PaCO₂ change p-value
0	12.5 (11.2–15.5)	14.5 (12.0–16.9)	0.005	30.6 (29.1–33.6)	33.2 (32.3–38.3)	0.005	4.7 (4.3–5.6)	4.7 (4.2–5.3)	1.000
1	15.6 (12.5–17.3)	17.1 (14.0–20.2)	0.005	33.8 (32.6–37.7)	36.7 (35.5–42.9)	0.005	4.6 (4.0–5.2)	4.8 (4.1–5.5)	0.203
2	17.3 (12.9–20.4)	19.4 (15.2–22.4)	0.005	37.3 (34.7–43.6)	41.0 (39.8–49.1)	0.013	4.7 (4.0–5.4)	4.7 (4.0–5.4)	0.612
3	18.7 (13.3–22.7)	22.4 (17.3–26.8)	0.005	41.9 (37.7–44.0)	46.8 (44.0–51.9)	0.019	5.0 (4.1–5.5)	4.8 (4.3–5.3)	0.284

Data presented as median (IQR).

When the modification was fitted to conserve oxygen it significantly reduced wall oxygen consumption by median (IQR) −1.0 (−1.25 to −1.00) L/min (p = 0.003), without affecting PaO₂ (p = 0.760), PaCO₂ (p = 0.508) or FiO₂ (p = 0.759).

Discussion

Our modification offers the potential either to deliver a higher FiO₂ to an individual patient using a domiciliary ventilator or, if applied to many patients, to reduce the oxygen consumption of an institution without reducing the FiO₂ delivered to patients. By machining an adaptor with the addition of components that are globally and cheapy produced, it could provide a local solution in situations where oxygen demand is increased,^1
–4,6 or in natural disasters or conflict where supply may be interrupted or reduced.^6,7 The modification has other possible benefits; it may prevent the occasional requirement for a second oxygenator in patients requiring high levels of FiO₂ on home ventilation, and has potential environmental and economic benefits by reducing oxygen production requirements.^8,9

Limitations

Our ethical committee forbade us enrolling patients by gaining consent from their next of kin and stipulated participants be able to give their own consent. Thus, participants were at the recovery stage of critical illness with modest FiO₂. This could limit the generalisability of this data where patients require higher levels of FiO₂,¹⁰ but interestingly the modification reduced walled oxygen consumption more in participants with higher FiO₂ requirements (0.35 and 0.40) than with lower FiO₂ requirements (0.28–0.33) by 2 L/min versus 1 L/min respectively.

Concluding, a simple modification can increase in FiO₂ and PaO₂ without requiring more oxygen from the wall supply, which may be a valuable modification in circumstances where there is a relative shortage of oxygen.

Footnotes

Acknowledgements

The authors gratefully acknowledge Dr Donna Hall, Robin Hardie, and the medical and nursing staff at Harefield Hospital for facilitating this study, and the patients for agreeing to participate in the study.

Declaration of conflicting interests

The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: MIP is a paid consultant for Philips Respironics; however, Philips had no role in this study. TOJ, PG, TMS, YM declare no conflicts of interest.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The study was funded by the Royal Brompton and Harefield Hospitals Charity Fellowship, who had no role in the design, collection, analysis, interpretation of the data or writing the manuscript.

ORCID iD

Timothy O. Jenkins

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In vivo assessment of a modification of a domiciliary ventilator which reduces oxygen consumption in mechanically ventilated patients