Pmdi’s need Counters and Breath Operated Actuators
Pmdi’s need Counters and Breath Operated Actuators.
Some years ago my wife unexpectedly had an asthma attack. It was 3 in the morning and it took half an hour to get her to A&E. Salbutamol/nebuliser treatment for 20 minutes restored normality. Review by a consultant revealed nothing of significance but since then she kept a salbutamol pmdi handy, with occasional use.
Latterly, onset of the characteristic asthma cough signalled increasing severity, and with a little pressure from daughter GP, she progressed through use of an SABA to an LABA + steroid. Our NHS GP perfectly reasonably uses Chiesi’s Fostair (BDP + formoterol) rather than more expensive treatments available.
At this stage I started to take more interest in how patients use pmdi’s.Two features immediately emerged, a third later. The first was how on earth did she know when the container was approaching empty? This becomes a really serious issue when you have actually experienced a family member in an asthma attack. For years we have all been involved in this problem of counters and inhalers, often practically, and certainly at innumerable conferences. Actually faced with the situation it is really quite extraordinary; what on earth are we doing marketing these things with no clear means of determining how many doses are left? I found myself shaking the container to guess how much remained. I didn’t even attempt the ludicrous water immersion technique so beloved of old text books. In desperation I contacted our good colleague Gaetano Brambilla at Chiesi who kindly provided me with the canister average fill weight. With use of a set of kitchen scales and (as the Americans say) doing the maths, we can now get some quantitative idea of where we are. I discovered you really can quite easily lose track of how many doses have been taken when occasional extra doses are needed in the small hours – and they are – between the standard am and pm treatments. And kitchen scales are not really up to this…..
We have to do something about this.
Inevitably co-ordination of dose administration was the other problem. Yes, I endeavoured to teach the technique – exhale, insert mouthpiece, start to inhale then press – sounds easy but it turns out to be really difficult to grasp. I quickly realised pursuing tuition of use of a pmdi is rather like trying to teach your wife to drive – don’t attempt it! And yes, our GP has an asthma nurse!! I have gone down the spacer route but they are just clumsy and we all know they stay in the cupboard. I really don’t have to labour this experience, you all have heard the stories.
These two problems with pmdi’s are well known to us but it seems they have become like “white noise”, we just don’t recognise them any more. We really must do something about them and quickly. The weary excuse that suppliers cannot afford to introduce counters and breath operated actuators simply isn’t good enough. Patients are at risk, really!
What are we, the “experts”, going to do about it?
Then, recently, a curious third problem has emerged. Using Gaetano’s kindly supplied fill weight data I determined the weight loss after a month from the canister. When my wife finally discarded the inhaler after 28 days use, I weighed it and to my surprise found it had only lost about 4g against a nominal average fill weight of 9.3g. Gentle shaking did not reflect any substantial inertial propellant movement in the canister that I could detect, so I tried discharging any remaining doses (in the open, H&S of course) and in strong sunlight – you can see the aerosol cloud more easily. To my horror, I discharged 70 doses before nothing else came out. So my wife over a period of 28 days had actually only fired off 57 shots when meticulously taking 2 shots, twice a day i.e. the prescribed 112 doses.
What has happened? Are the valve springs too strong for some patients? Has anyone actually looked into this? I cannot recall seeing any work in this area. Presumably the spring strength is based on what the valve needs for closure. Did anyone think of the patient’s ability to operate it? Are we overly concentrating on getting immaculate laboratory data and our dose testing apparatus has failed to be calibrated against the patient’s ability to use the pmdi?
And what are we going to do about it?
John Bell
11 March 2012






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