The Science Journal of the American Association for Respiratory Care

2006 OPEN FORUM Abstracts

THE EFFECT OF REPEATED NEBULIZATION OF NORMAL SALINE THROUGH A SMALL VOLUME NEBULIZER ON DELIVERED PARTICLE SIZE

Sorenson HM.  Fling D, Wilson W, Rodriguez A, and Lombardo A .  The University of Texas Health Science Center, San Antonio, TX.

Background:  There is tremendous growth in the inhaled drug market both in the USA and worldwide.

 The pulmonary drug delivery market is projected to exceed $36 billion in sales by 2006.  Small volume nebulizers (SVN) are used in many hospitals to deliver aerosolized medications to pulmonary patients.  Stable pulmonary patients also use SVNs in the home for extended periods of time. To effectively deliver aerosol to the parenchyma, devices should deliver a stable mist with particles in the range of 0.5µm to 4.70µm.  Because most medications delivered by SVNs are diluted in normal saline (0.9%), this study was conducted to determine if repeated nebulization with normal saline had any effect on the delivered particle size. 

Method: SVN treatments similar to those given in a hospital were simulated in the laboratory using normal saline.  A Hudson RCI MicroMist SVN was used.  3.0 mls of 0.9% saline was nebulized using an air flowmeter set at 8 LPM, a total of 42 times, equivalent to 7 days of Q4 treatments.  Between simulations, all of the nebulizer components were placed on a paper towel and allowed to air dry.   An additional 42 breathing treatments were simulated with the same SVN to mimic 14 days of Q4 treatments.  The average run time for 42 and 84 simulations respectively was 9.13 minutes and 9.15 minutes.  Particle size was measured using a Model 3321 Aerodynamic Particle Sizer manufactured by TSI, Inc. Measurements were made after 42 uses and again after 84 uses.  For comparison purposes, particle size from a new Hudson RCI MicroMist SVN was also measured. 

Results:
See Table 1.0

Conclusion:
This study indicates that repeated nebulization of normal saline through an SVN results in change in particle size; in number per cm3, surface area per cm3 and in mass per meter3 (shown on table below). There were significant differences in particles between the new SVN, one used 42 times and then reused an additional 42 times.  Significant changes happened between the 42nd and 84th simulated treatment. Measurements were not done between the 42nd and 84th nebulization. Limitations to this study include the use of two different SVNs. Failure to initially measure particle size required the use of a new Hudson RCI MicroMist SVN at the completion of the study, to determine particle size from an unused SVN; additionally, repeated measurements were not done; only a single measurement was done on the new SVN, once after 42 uses and again after 84 uses. Based on the results of this study it is our conclusion that a study similar to this should be repeated.  If the results are comparable, further studies may be warranted to explore what role different medications added to normal saline have on particle size generation from repeated use of SVNs.

Table 1.0 Nebulizer Study; Mass (mg) per Cubic Meter

  N Mean (SD) SEM Median Range P-value
After 0 nebulizations 51 0.59 (0.92) 0.13 0.12 0 to 3.77  
After 42 nebulizations 51 0.56 (0.87) 0.12 0.13 0 to 3.7  
After 84 nebulizations 51 3.61 (6.41) 0.9 0.32 0 to 25.7  
Change from 0 to 42 51 -0.04 (0.07) 0.01 0 -0.27 to 0.02 0.091
Change from 0 to 84 51 3.02 (5.49) 0.77 0.2 0 to 21.93 <0.0011
Change from 42 to 84 51 3.05 (5.55) 0.78 0.19 0 to 22 <0.0011
Linear trend           <0.0012


1.  Sign test

2.  Repeated measures linear model of log (mass) on usage (0, 42, 84)


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