Kirkman Emrys, Pope C, Wilson C, Woolley T, Watts S, Byers M
CBR Division, Defence Science and Technology Laboratory Porton Down, Salisbury, UK
Defence Medical Services, Lichfield, UK.
BMJ Mil Health. 2024 Jun 23. doi: 10.1136/military-2024-002727.
Administering supplemental oxygen is a standard of care for trauma casualties to minimise the deleterious effects of hypoxaemia. Forward deployment of oxygen using pressurised cylinders is challenging, for example, logistics (weight and finite resource) and environmental risk (fire and explosion). Oxygen concentrators may overcome these challenges. Although previous studies successfully demonstrated fractional inspired oxygen (FiO) >0.8 using oxygen concentrators and ventilators, the systems did not fulfil the size, weight and power requirements of agile military medical units. This study evaluated whether a modular system of commercially available clinical devices could supply high FiO to either ventilated or spontaneously breathing casualties.
As a proof of principle, we configured an Inogen One G5 oxygen concentrator, Ventway Sparrow ventilator and Wenoll rebreather system to ventilate a simulated lung (tidal volume 500 mL). Casualty oxygen consumption (gas withdrawal inspiratory limb) and carbon dioxide (CO) production (CO added expiratory limb) were simulated (respiratory quotient of 0.7-0.8). Three circuit configurations were evaluated: open (supplementary oxygen introduced into air inlet of ventilator); semiclosed (ventilator replaces rebreather bag of Wenoll, oxygen connected to either ventilator or Wenoll); and semiclosed with reservoir tubing (addition of 'deadspace' tube between ventilator patient circuit and Wenoll). Data presented as mean and 95% reference range.
There were modest increases in FiO with increasing Inogen settings in 'open' configuration 0.23 (0.23-0.24) and 0.30 (0.28-0.32) (Inogen output 420 and 1260 mL/min, respectively). With the 'semiclosed' configuration and oxygen added directly into rebreather circuit, FiO increased to 0.36 (0.36-0.37). The addition of the 'reservoir tubing' elevated FiO to 0.78 (0.71-0.85). FiO remained stable over a 4-hour evaluation period. Fractional inspired carbon dioxide CO increased over time, reaching 0.005 after 170 (157-182) min.
Combining existing lightweight devices can deliver high (>0.8) FiO and offers a potential solution for the forward deployment of oxygen without needing pressurised cylinders.
