ALBUTEROL DELIVERY IN A MODEL OF MECHANICAL VENTILATION - COMPARISON OF METERED-DOSE INHALER AND NEBULIZER EFFICIENCY

Using an in vitro model, we compared efficiencies of jet nebulizers an d metered-dose inhalers (MDI) with actuator devices to deliver albuter ol in various conditions of mechanical ventilation. Factors tested inc luded influence of humidification, MDI actuator device (Aerovent(R) sp acer or Marquest 172275 MDI adaptor), and synchronization of MDI to th e respiratory cycle. With the nebulizer (AeroTech II(R)) filled with 2 .5 mg albuterol sulfate in 3 mi water and run until dry, inhaled mass was 42 +/- 2.6% and mass median aerodynamic diameter (MMAD) was 1.3 mu m on a nonhumidified circuit. With the MDI+ Aerovent(R), the inhaled mass percentage per 90 mu gm puff was 15.4 +/- 0.2% with humidificatio n and 25.1 +/- 3.7% without humidification, actuations being synchroni zed with the beginning of inspiration and separated by a 1-min pause. Failure to synchronize actuations with inspiration or to pause 1 min r esulted in significant reductions in inhaled mass (by 35 and 72%, resp ectively). The Marquest adaptor was less efficient, with an inhaled ma ss of 7.2 +/- 0.7% under optimal conditions. Metered-dose inhaler actu ation during expiration resulted in relatively large particles (MMAD = 2.0 mu m). All other MDI actuations led to essentially biphasic distr ibutions, with particles greater than 1 mu m following a distribution similar to the nebulizer and the overall MMAD estimated to be 0.22 mu m. The AeroTech II(R) delivered a cumulative 1,000 mu g of drug (2,500 x 0.40) over 40 min. To achieve that amount, the MDI connected to the Aerovent(R) and used in its most efficient sequence would require 45 timed puffs (90 mu g per puff, 25.1% mean inhaled mass) and take 45 mi n of an experienced therapist's time. We conclude that nebulizers and MDI/spacers can both be effective in delivering aerosolized medication s, but drug delivery can be significantly reduced if proper technique in setting up and using both devices is not followed. Physicians and r espiratory therapists should be formally trained in the principles of aerosol delivery with mechanical ventilation.