Bench Evaluation of Oxygen Delivery Using Portable Ventilators Paired With Portable Oxygen Concentrators

Abstract

Background: Military transport of critically ill/injured patients requires judicious use of resources. Maintaining oxygen (O₂) supplies for mechanically ventilated is crucial. O₂ cylinders are difficult to transport and add the risk of fire in an aircraft. The proposed solution is the use of a portable oxygen concentrator (POC) to supply O₂ for mechanical ventilation. As long as power is available, a POC can provide a continuous supply of O₂. Evidence suggests that 3 L/min of O₂ could manage 2/3 of the mechanically ventilated aeromedical transport patients. Methods: We evaluated two each of the AutoMedx SAVe II, Hamilton T1, Zoll 731,and one Ventec VOCSN portable ventilator over a range of settings paired with two Caire SAROS POCs. The VOCSN operates from an internal O₂ concentrator using pulsed dose delivery equivalent to 6 L/min continuous flow O₂. Each ventilator was attached to one chamber of a Michigan Instruments Training Test Lung (TTL). Output from the POC was bled-in to each ventilator via the mechanism provided. A Fleisch pneumotach was placed between the ventilator circuit and the TTL to measure delivered tidal volume (V_T) and a fast response O₂ analyzer (Oxigraf) sampled gas from the TTL to measure FIO₂. Deadspace was added between the ventilator circuit and TTL for pulsed dose delivery. Ventilator parameters and FIO₂ were continuously measured and recorded for later analysis. One-way ANOVA was used to determine statistically significant differences (P < .05) in FIO₂ at each ventilator/POC setting. Results: Delivered FIO₂ varied widely between ventilator models and between devices of the Hamilton T1 ventilators. Differences in FIO₂ at each ventilator/POC setting was statistically significant (P < .05) but not all were clinically important. The SAVe II delivered the highest FIO₂ at all conditions using a V_T of 700 mL owing to limited VE capabilities. The highest delivered FIO₂ was 84.6% ± 0.5 at the 250 mL V_T settings using 2 POCs (P < .001). The Zoll 731 delivered the highest FIO₂ at each ventilator setting using both POCs. Calculated FIO₂ displayed on the VOCSN in pulsed dose mode was within ± 2% absolute of measured FIO₂. Conclusions: Oxygen delivery utilizing POCs is dependent upon multiple factors including ventilator operating characteristics, ventilator settings, and the use of pulsed dose or continuous flow O₂. Careful patient selection would be paramount to provide safe mechanical ventilation using this method of O₂ delivery.