2004 OPEN FORUM Abstracts
Providing Oxygen Therapy During Exhaled Breath Condensate Collection Using the RTube™
Brian
K. Walsh, RRT-NPS, RPFT; John Vaughan; John Hunt, MD. University
of Virginia Pediatric Respiratory Medicine; Charlottesville, Virginia
Background:
Measurement of biomarkers in exhaled breath condensate (EBC)
provides a new non-invasive research tool to study airway chemistry
and inflammation in lung disease. These assays have potential
clinical utility in patient management. The RTube™ is a single
patient use disposable EBC collection device through which a patient
orally breathes, utilizing 2 one way valves that allow room air to be
inhaled while directing all exhaled airflow through a 9 inch
polypropylene collection chamber cooled by an aluminum sleeve. This
process condenses the aqueous components of exhaled breath, as well
as enlarging and trapping particles that are evolved by turbulent
flow from the airway lining fluid. This very safe system is highly
applicable to non-invasive collection of exhaled breath constituents
even in patients with marked pulmonary insufficiency, and we
therefore have undertaken to expand its utility by developing simple
means to provide supplemental oxygen during the 3-10 minutes that it
takes to collect EBC.
Methods:
An oxygen adapter and 6 inch corrugated tubing were connected to the
inspiratory valve of the RTube™. The oxygen adapter was placed
proximal to the inspiratory valve which allows the 6 inches of
corrugated tubing to become a 50 ml oxygen reservoir. Starting flows
were calculated using a low flow FIO2 estimating equation:
FIO2
(estimated) = O2 + 0.21 (V insp – O2)
(V insp)
Three
levels of spontaneous minute ventilation (MV) by one healthy
volunteer were used to test the equation and oxygen delivery set-up.
A FIO2 of .35 was targeted to be delivered. Minute
ventilations of 12, 8, and 3 liters per minute were chosen and
measured by a Wright Respirometer. Average inspiratory flows were
calculated by multiplying the subject’s minute ventilation by
the sum of the observed I:E ratio. FIO2 was analyzed
proximal to the mouth piece using a MSA Miniox oxygen analyzer.
Results:
| MV target (l/min) | FIO2 target | Observed I:E ratio | Measure MV | Oxygen flow added to new RTube™ Reservoir (L/min) | Calculated inspiratory flow (L/min) | Average Measured FIO2 |
| 12 | .35 | 1:2 | 12.6 | 6.5 | 36 | .36 |
| 8 | .35 | 1:2 | 7.8 | 4.2 | 24 | .38 |
| 3 | .35 | 1:2 | 3.6 | 1.8 | 9 | .39 |
Conclusion:
Oxygen therapy can be successful provided during RTube sampling
by simply attaching oxygen with a small reservoir to the inspiratory
limb of the device. As with all low flow oxygen devices FIO2
is variable depending on the patients inspiratory flow and oxygen
applied to the device. Our results show a higher measured FIO2
than targeted FIO2 at lower inspiratory flow due to the
constant reservoir size. Simple monitoring with a pulse oximeter
would allow the clinicians to titrate the oxygen flow to the desired
oxygen delivery during sampling. Precise oxygen titration can also
be provided by changing the length of the reservoir tubing.