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.