Water accumulation in metered dose inhaler spacers under normal mechanicalventilation conditions

OBJECTIVE: The purpose of this study was to compare the water accumulation in 3 types of metered dose inhaler (MDI) spacer shapes in-line in a ventila tor circuit, in 2 positions over 2-, 4-, and 6-hour time periods through th e use of heated- and nonheated-wire ventilator circuits. DESIGN:The study design was prospective, quasiexperimental, and random assi gnment. SETTING: The study was conducted in a university laboratory. MATERIALS: Three brands of MDI spacers (OptiVent, ACE, AeroVent) were teste d. OUTCOME MEASURES: Grams of water accumulation were measured. INTERVENTION: Distilled water accumulation was measured in 3 brands of MDI spacers in 0 degrees and 45 degrees positions at 2-, 4-, and 6-hour time in tervals. Water accumulation was measured in each spacer by calculating the differences between pretest (dry) weights and posttest (wet) wrights throug h the use of an analytical balance; A Marquest SCT-3000 servo-controlled hu midifier with heated-wire ventilator circuit was used with a room temperatu re range of 21.7 degreesC-22.8 degreesC (71 degrees -73 degreesF) and a rel ative humidity range of 57%-65%. RESULTS: Multivariate repeated measures analysis demonstrated a difference between brands (P < .001). The amount of water accumulated during 6 hours ( time variable) was significantly different (P < .001), as was the interacti on between time and "spacer brand" (with Greenhouse-Geisser adjustment). Th e interaction of time and position was also significantly different (P = .0 01). Water accumulations at a 45 degrees angle were: AeroVent 0.765 +/- 0.1 52 g; OptiVent 1.894 +/- 0.228 g; and BCE 4.043 +/- 0.665 g through 6 hours of use. CONCLUSIONS: We found that water accumulation was a result of the type of s pacer, position of the spacer, and lime that the spacer was left in-line. A ll 3 brands of spacer collected less than 5 mt of water over 6 hours in eit her position. Heated-wire circuits accumulated less water than nonheated-wi re circuits and may be safer when using MDI spacers.