The Science Journal of the American Association for Respiratory Care

2006 OPEN FORUM Abstracts

IMPACT OF VARIOUS O2 DEVICES AND FLOWRATES ON THE PERCENT OXYGEN MEASURED IN EXPIRED ERV GAS

Bob Langenderfer, MEd, RRT-NPS, Asst. Prof and DCE Northern Kentucky Univ. Highland Heights, KY.

Background:  Evaluating oxygen therapy techniques is problematic because of difficulties in measuring the real FiO2 achieved.  Gas sampling via pharyngeal catheter disrupts normal ventilation and fails to measure the actual % oxygen within the lung.  In an attempt to evaluate various oxygen devices and flowrates, we tried a new approach. We measured the O2% in the ERV, the last portion of gas exhaled with effort, after multiple subjects breathed oxygen for 7+ minutes from various devices and flowrates. We then calculated the FiO2 using the (modified) alveolar gas equation.

Methods: Fifteen volunteers each breathed oxygen for 7+ minutes from various devices/flowrates. After tidal exhalation, ERV gas was collected, and the % oxygen measured with a calibrated VacuMed lab O2 analyzer. To calculate FiO2 and to assure normal breathing, PETCO2 was measured.

Results: On room air the average expired ERV was 17 % oxygen. (N=15)

     Device:         Flow: NC 2 lpm Close Os NC 2 lpm Open Os 28%Venti    at 6 lpm NC 6 lpm Close Os NC 6 lpm Open Os
Av.ERV %    21.4%     21.0%     22.7%     32.4%     31.2%
N;  range 11; 19-23 11; 18-23 6; 21-24% 12; 28-36 10; 24-38
Calc FiO2    27.2%     26.4%     28%     37.8%     36.5%
     Device:         Flow: Standard NC 10 l. HighFlow NC 10 l. HighFlow NC 14 l. NRB 15 l. SafeVent NRB 15 l.  No Vent
Av.ERV %     40.4%     38.4%     41.9%     55.9%     59.3%
N;  Range 17; 30-51 10; 31-47 12; 32-53 12; 48-62 9; 48-65
Calc FiO2     45.7%     44%     47%     61.6%     65%
     Device:         Flow: SmplMsk   10 lmp Oxymizer  1 lpm Oxymizer    6 lpm PlseDose  = 2 lpm PlseDose  = 6 lpm
Av.ERV %     36.5%     22.1%    33.7%     21.9%     27.4%
N;  Range 6; 33-40 6; 21-23 6; 29-37 8; 19-24 11; 24-35
Calc FiO2     42.2%     27.3%     38.9%     27.4%     32.5%

Conclusions:  Percent O2 in ERV gas is a useful tool to evaluate oxygen therapy devices and flowrates.  Open-mouth breathing lowers FiO2 slightly. NC flows above 6 lpm do increase ERV O2%, but with less increase at flows above 10 lpm.  Equivalent ERV O2 % is achieved by NC 2 lpm, 28% venturi, 1 lpm Oxymizer and Salter PulseDose set = to 2 lpm.  Salter PulseDose = 6 lpm gives lower FiO2 than cannula at 6 lpm. NRB at 15 lpm only gives 62-65% O2, with the higher FiO2 when using all 3 flap valves.

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