MEASURING NEBULIZER OUTPUT - AEROSOL PRODUCTION VS GRAVIMETRIC ANALYSIS

Study objectives: The function of jet nebulizers has been measured tra ditionally by gravimetric methods, ie, by weighing nebulizers before a nd after nebulization. Newer techniques measure aerosol output directl y by analyzing aerosolized drug or tracer, ie, radioactive Tc-99m. Bec ause of evaporation, the equivalence of these methods is uncertain. Th e aim of this study was to determine if the gravimetric method is an a ccurate measure of aerosol production under different conditions of ae rosol generation (ie, nebulizer type, flow rate, pressure, volume fill , and concentration of solution used to nebulize a drug). Methods: In the first phase of the study, we measured the aerosol output of nine c ommercially available jet nebulizers (AvaNeb; Up-Draft-Hudson RCI; Cir rus-Intersurgical Inc; DeVilbiss 646-DeVilbiss; Powermist-Hospitak, In c; Respirgard II-Marquest Medical Products; Seamless-Seamless/Dart Res piratory; Salter; Salter Labs; Airlife-Baxter Health Care) run under c ommonly used conditions (2.5 mL volume fill, 2.0 mL normal saline solv ent, 0.5 mL albuterol, flow of 6 L/min, and pressures averaging 15.0+/ -2.3 [mean+/-SD] pounds per square inch [on the] gauge [psig] provided by a DeVilbiss PulmoAide compressor) with simultaneously measured gra vimetrics and filtered radioactivity. Each nebulizer was run to drynes s with data acquired every 2 min. The change in the weight of the nebu lizer and radioactivity captured on the filter were expressed as perce ntages of the total in the nebulizer solution. In the second phase of the study, die experiments were repeated using the same nebulizers wit h a volume fill of 5 mt (diluted to half normal saline solution plus a lbuterol), flow of 10 L/min, and pressures of 35.6+/-8.8 psig. Results : The cumulative (sum of all 2-min runs) weight loss for each individu al nebulizer ranged from 25.00 to 64.55% and cumulative aerosol captur ed varied from 12.63 to 38.76%. While different, the weight loss and a erosol captured were closely correlated (y=-0.62+0.62x; r=0.961, p<0.0 001). Changing volume fill and concentration of solvent did not affect this correlation (p=0.921 and 0.373, respectively). However, changing flow from 6 L/min to 10 L/min significantly (p=0.02) affected the rel ationship (y=-3.80+0.83x; r=0.969, p<0.001). Conclusions: When compare d with direct methods such as filtering generated particles, the gravi metric method of assessing nebulizer function overestimates aerosol ou tput by 1.8+/-0.18 times, presumably because of the loss of solvent du ring nebulization. However, the relationship between methods is predic table and appears unaffected by changing the type of nebulizer, volume fill, and concentration of solvent. Changes in nebulizer flow and pre ssure significantly affected the correlation. Gravimetric methods can be used as simple and convenient screening techniques for comparing je t nebulizers under a wide range of experimental conditions.