The Science Journal of the American Association for Respiratory Care

2012 OPEN FORUM Abstracts


Thomas Blakeman1, Dario Rodriquez2, Richard Branson1; 1Department of Surgery, University of Cincinnati, Cincinnati, OH; 2Center for Sustainment of Trauma and Readiness Skills (CSTARS), United States Air Force, Cincinnati, OH

Background: Hypoxemia secondary to reduced barometric pressure is a complication of ascent to altitude. Current medical operations in support of warfighters in Afghanistan often require ascent to 14,000 feet or more in unpressurized aircraft during evacuation of casualties. Aboard aircraft, oxygen can be delivered using a continuous flow of oxygen from liquid or compressed gas sources or via an oxygen concentrator. We designed a study to compare the reversal of hypobaric hypoxemia at 14,000 feet with continuous flow oxygen from a cylinder and pulsed dose oxygen from a portable concentrator. Methods: Thirty healthy volunteers were randomized to one of three study arms, placed in an altitude chamber and ascended to 14,000 feet (PB 428 mm Hg). Subjects breathed room air for 10 minutes to induce hypoxemia. If the oxygen saturation fell below 82% or at the 10 minute time point oxygen was delivered via a nasal cannula from a cylinder at 1, 2, or 3 lpm of continuous flow for 10 minutes. Then the subjects again breathed room air at altitude for 10 minutes. The equivalent dose of pulsed oxygen from the concentrator (16, 32, or 48 mL) was placed on the subjects for 10 minutes. If needed in order to match the SpO2 while on continuous flow, the pulse dose was increased in steps. Subjects were then returned to sea level. Measurements of SpO2, EtCO2, RR, HR, Hgb, and tissue oxygenation (StO2) were continuously recorded throughout each “flight”. Results: SpO2 varied both between and within study arms. The 1 lpm/16 mL arm had the widest SpO2 range: 89% - 99% (mean 93.4 % ± 3.1) and 87% - 97% (mean 91.5% ± 3.4) respectively and was not able to correct hypoxemia (SpO2 = 90%) in every subject. The 2 lpm/32 mL arm range was 95% - 98% (mean 69.8% ± 0.9) and 88% - 96% (mean 92.0 % ± 2.5) respectively. The 3 lpm/48/mL arm was able to correct hypoxemia in each subject (mean 97.7% ± 1.3 and 94.1% ± 2.9) respectively. Figure below shows recorded data from a sample flight. Conclusions: At 14,000 feet, 1 – 3 lpm continuous flow oxygen corrected hypoxemia in all but one subject (SpO2 89%). Although using the concentrator in the 16 mL and 32 mL arms had more subjects with SpO2 < 90%, the increased pulse dose required to obtain SpO2 equivalent to continuous flow was well within the device’s capability. Oxygen concentrators may be an alternative to liquid oxygen or cylinders for use by during aeromedical evacuation. Key words: oxygen, hypobaric, concentrator, hypoxemia, aeromedical. Sponsored Research - None