3b. Pressurized Metered Dose Inhaler Flashcards
What is a pMDI?
pMDI: Pressurized canister with prescribed drug (micronized powder or aqueous solution) in volatile propellant combined with surfactant and dispersing agent.
Advantages of pMDI (4)
Portable, Compact, Easy to Use, Provides Multidose Convenience
Which patients pMDIs are preferred for? (2)
Spontaneously breathing patients, and patients who are intubated and undergoing mechanical ventilation
Disadvantages of pMDI (3) and limitation (1)
Hand-breath coordination required (which can be difficult), Risk of Abuse, Higher percentage of pharyngeal deposition.
If there’s not dose counter ➔ difficult to determine how much dose remaining
What does the pMDI administer? (3)
Administer bronchodilators, anticholinergics, and steroids
How do the pMDI generate aerosol?
With the nozzle down, the volatile suspension fills metering chamber (used to control the amount of drug delivered).
And when the canister is pressed, a hole in the metering valve aligns with the metering chamber and quickly forces the metered dose through this hole and through the actuator nozzle.
How long does aerosol production take?
20 msec
What’s a plume and what’s the velocity?
When the liquid suspension is forced out of the pMDI ➔ it forms a plume and propellants vaporizes.
Velocity ➔ approx 15 m/sec
What are 2 propellants used and what’s the difference?
Chlorofluorocarbons (CFCs) ➔ used before but prohibited/banned because of the effect on global warming (destroys 100k molecules of stratospheric ozone)
Hydrofluoranealkane (HFA) ➔ newer and more environmental friendly and clinically safer ➔ also changed and improved the components
What’s another variation of pMDI and how does it work?
Breath-actuated pMDI ➔ where there’s a trigger that activates when inhaling
What’s the advantage and limitation of breath-actuated pMDIs?
Advantage ➔ offers an alternative for individuals who find it difficult for hand-breath coordination.
Limitations ➔ Low flow rate won’t trigger the dose delivery mechanism. (infants and children). Less drug deposition to lungs and more in the oropharynx
What is the purpose of propellants in a pMDI? And how much does it take up
Volatile Propellants are needed to propel or provide that ‘thrust’.
It is combined with a surfactant and dispersing agent.
Takes up approx 60-80% of the canister
What’s the purpose of a Metering Valve?
Metering Valves are responsible for metering/regulation of reproducible volume or dose. The elastomeric valves are responsible for sealing and preventing drug loss/leakage.
What’s the purpose of an actuator? (and whats the nickname for it)
An actuator (frequently referred to as a boot) is partially responsible for particle size based on the length and diameter of nozzle of various pMDIs
What’s the mechanism of a Soft Mist Inhaler?
SMI uses mechanical energy in the form of a tension spring to create an aerosol from liquid solutions to produce a low-velocity spray (10mm/sec) lasting 1.5 seconds
How do you operate a Soft Mist Inhaler?
Twist the body of the device to load an internal spring, Place mouthpiece in between lips and press button.
Required hand-breath coordination but has a longer aerosolization time ➔ greater percentage of emitted dose
What’s priming? and whats the purpose?
When you shake the device and release one or more (1-4) sprays into the air. It’s to mix the drug and propellant to achieve an adequate dose delivery.
When and how often should you prime?
When it’s brand new. When it hasn’t been used in awhile (4-6 hours) depending on the label.
Factors affecting pMDI performance (4)
Temperature, Nozzle size and Cleanliness, Priming, and Timing of Actuation Intervals
How does temperature affect MDI performance?
This problem usually occurs in CFCs pMDI, when the temperature is low (<10 C), there’s a decrease in percentage of the drug output. However, it’s not so much of a problem with HFAs
How does Nozzle Size and Cleanliness affect MDI performance?
Cleanliness: when theres debris building up in the nozzle, the emitted dose is reduced. And debris can also end up in the airways.
Nozzle Size: it’s specific to the pMDI, and it also affects particle size
How does the Timing of Actuation Intervals affect MDI performance? and how long should you wait?
Manufactures recommend 30 sec-1 minute between actuations. This pause allows the canister to go back to room temp, because it cools right when you actuate it.
What are the 2 primary techniques for pMDIs? And what’s the difference between them?
Open-mouth: Actuated several cm in front of opened mouth ➔ less oropharyngeal impaction and increase lung dose (particles reduce to a respirable size)
Closed-mouth: Placed between teeth and actuated while inhaling
What technique would you recommend to a patient?
I would first recommend the patient to get a spacer. If they refuse, the open mouth technique is more effective but difficult. I would teach them both (closed-mouth would be better if they had to take it outside) If given anticholinergic agents, I would suggest close-mouth technique because it can affect the eyes if they glaucoma.
