Background: Current pressurised metered dose asthma inhaler (pMDI) propellants are not inert pharmacologically\nas were previous chlorofluorocarbons, have smooth muscle relaxant� partial pressure effects in the lungs and inhaled\nhydrofluoroalkane 134a (norflurane) has anaesthetic effects. Volumes of propellant gas per actuation have never been\nmeasured.\nMethods: In-vitro studies measured gas volumes produced by pMDIs on air oxygen (O2) levels in valved holding\nchambers (VHC) and the falls in O2% following actuation into lung ventilator delivery devices.\nResults: Volumes of propellant gas hydrofluoroalkane (HFA) 134a and 227ea and redundant chlorofluorocarbons\n(CFC) varied from 7 ml per actuation from a small salbutamol HFA inhaler to 16 ml from the larger. Similar-sized CFC\npMDI volumes were 15.6 and 20.4 ml. Each HFA salbutamol inhaler has 220 full volume discharges; total volume of\ngas from a small 134a pMDI was 1640 ml, and large 3885 ml. Sensing the presence of liquid propellant by shaking\nwas felt at the 220th discharge in both large and small inhalers. Because of a partial pressure effect, VHC O2% in air\nwas reduced to 11% in the smallest 127 ml volume VHC following 10 actuations of a large 134a salbutamol inhaler.\nThe four ventilator delivery devices studied lowered 100% oxygen levels to a range of 93 to 81% after five actuations,\ndepending on the device and type of pMDI used.\nConclusion: Pressurised inhaler propellants require further study to assess smooth muscle relaxing properties.
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