Water accumulation in metered dose inhaler spacers under normal mechanical ventilation conditions

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 ventilator circuit, in 2 positions over 2-, 4-, and 6-hour time periods through the use of heated- and nonheated-wire ventilator circuits.

The study design was prospective, quasiexperimental, and random assignment.

The study was conducted in a university laboratory.

Three brands of MDI spacers (OptiVent, ACE, AeroVent) were tested.

Grams of water accumulation were measured.

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 intervals. Water accumulation was measured in each spacer by calculating the differences between pretest (dry) weights and posttest (wet) weights through the use of an analytical balance. A Marquest SCT-3000 servo-controlled humidifier with heated-wire ventilator circuit was used with a room temperature range of 21.7 degrees C-22.8 degrees C (71 degrees -73 degrees F) and a relative humidity range of 57%-65%.

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 interaction between time and "spacer brand" (with Greenhouse-Geisser adjustment). The interaction of time and position was also significantly different (P =.001). Water accumulations at a 45 degrees angle were: AeroVent 0.765 +/- 0.152 g; OptiVent 1.894 +/- 0.228 g; and ACE 4.043 +/- 0.665 g through 6 hours of use.

We found that water accumulation was a result of the type of spacer, position of the spacer, and time that the spacer was left in-line. All 3 brands of spacer collected less than 5 mL of water over 6 hours in either position. Heated-wire circuits accumulated less water than nonheated-wire circuits and may be safer when using MDI spacers.