The Science Journal of the American Association for Respiratory Care

2006 OPEN FORUM Abstracts

methodology of the determInation of actuations remaining in a metered dose inhaler

-Cristin Bridgefarmer, RRT, David Mussetter, BA, RRT, Tim Frymyer, BS, RRT, Vic Brewer, RRT, Larry West RPh,  Michael Trevino, MS, RRT, Gary Weinstein, MD, FCCP, Presbyterian Hospital of Dallas, Dallas, Texas.

Background: We are a 903 bed hospital in a major metropolitan area that utilizes a common canister protocol. Metered dose inhalers (MDIs), which are stored in the Pyxis, are administered to the patient using their own spacer. While performing a literature search regarding inhaled medication, we came across data questioning how the practitioner or patient would know when an MDI was empty. Unlike dry powder inhalers, which have a mechanism to signal when the level of medication is near depletion, MDIs have no such indicator. When presented to our staff therapists, their responses included: 1) float the inhaler in water, 2) shake it, or 3) perform a test puff; none of which have been supported within the literature. Our challenge is to provide accurate medication delivery regardless of the medication delivery device. The management team proposed using a clicker counter to keep track of how many puffs have been actuated per inhaler in use. This idea was brought to our key therapists, where it received less than favorable feedback. One proposed solution was to weigh the canisters to determine if that was an effective mechanism to determine when the MDI was empty. This study seeks to determine the utility of such an approach.

Method: We weighed 30 Andrx Pharmaceuticals, Inc., 17g Albuterol Inhalers from a common lot number. Using a digital scale (The Mettler Toledo PG802-s), the average weight per inhaler was 28.97 grams when full. Two inhalers were randomly selected from this lot and used for this study. The canister was shaken for approximately 20 seconds between each actuation. After each puff we placed the canister on the scale and documented its weight until no visible cloud was discerned.


  Number of total actuations Avg. weight per puff Final weight
Inhaler A 227 0.083 g ┬▒ 0.008 10.10 g
Inhaler B 222 0.086 g ┬▒ 0.007 10.01 g

  Weight after 100 actuations Weight after 150 actuations Weight after 200 actuations
Inhaler A 20.55 g 16.42 g 12.27 g
Inhaler B 20.38 g 16.05g 11.73 g

Conclusion: It is apparent that an inhaler which has been actuated greater than 200 times may still dispense a cloud. The composition of this cloud, however, is unknown. We propose that weighing inhalers can be used as a reliable indicator to ascertain when the inhaler should no longer be used. After weighing larger numbers of inhalers, reference cards will be produced detailing a specific weight at which the therapist would discard the canister. These cards would then be kept with scales which would be located near each PYXIS medstation. The therapist would then weigh the canister prior to patient rounds. Once the inhaler achieved the critical weight indicated on the card, it would be thrown away.

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