The Science Journal of the American Association for Respiratory Care

1995 OPEN FORUM Abstracts

RESISTANCE INCREASE IN A BREATHING CIRCUIT FILTER WHEN USED IN CONJUNCTION WITH CONTINUOUS NEBULIZED BRONCHODILATION

Leo Langga BS RCP RRT, Skip Garton RCP CRTT, Randy Scott BS RCP RRT, Ron Perkin MD, Douglas Deming MD, Tom Malinowski BS RCP RRT, Mark Rogers BS RCP RRT, Loma Linda University Children's Hospital, Loma Linda, California

INTRODUCTION: Breathing circuit filters (BCF) are commonly used in protecting the integral components of a ventilator's electronic spirometer. Current literature shows little clinical research on the increased resistance and potential increase in work of breathing that a BCF may impose when used in conjunction with continuous nebulized bronchodilation. We hypothesized that the resistance (R) created by a BCF may significantly increase over time.

Methods: To simulate in-line continuous nebulized bronchodilation delivery in conjunction with BCF usage, full strength (0.5%) albuterol was nebulized with a Heart^{TM} large volume nebulizer at a flowrate of 12 LPM. Standard large bore tubing, 1.5 meters in length, was attached proximally to the aerosol outlet port and distally to a Pall BB-50T BCF. The BCF was oriented vertically to facilitate drainage. At timed intervals (0, 10, 20, 25, 30, 35, and 40 minutes) the BCFs were removed from the circuit, and various flows (0.06, 0.13, 0.19, 0.26, and 0.32 L/s) were delivered through a Cole-Parmer calibrated rotometer. Pressure gradients were then measured using a Gould-Statham TC 131 differential pressure transducer connected to a Grass Model 7 chart recorder. Pressure measurement points were equidistant at 6.5 cm pre and post BCF center. Resistance was calculated from pressure gradients measured across each individual filter divided by standard flows delivered through a calibrated rotometer. The filter resistances obtained at the different timed intervals were then compared to those obtained before initiation of nebulization at equivalent standard flows.

Results: A total of 18 individual BCF's were tested, and a comparison performed between the resistances; pre-nebulization (control), and post-nebulization. A Two-way ANOVA analysis was then used between groups. The results were as follows:

T (min.)0 10 20 25 30 35 40

R mean1.33 2.07 11.68 16.52 31.06 40.527.61

(cmH_2O/L/s)

[Delta] R (%) na 56%778%1122% 2235% 2945% 1975%

T= time, R=resistance, [Delta]R=% increase when compared to pre-nebulization R.

The BCF's at 10 minutes had a statistically significant increase in R (pɘ.05). The consecutive resistances measured at 20, 25, 30, 35, and 40 minutes were also statistically significant (pɘ.05) for an increase in resistance.

Conclusions: The resistance imposed by BCF's is significantly increased over time and should be used with caution when applied with in-line continuous nebulized bronchodilation. Further studies need to be done to look at the effect of other types of medications on BCF resistance and the increase in work of breathing that may result.

OF-95-137

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