3b. Pressurized Metered Dose Inhaler

Question 1

What is a pMDI?

Answer 1

pMDI: Pressurized canister with prescribed drug (micronized powder or aqueous solution) in volatile propellant combined with surfactant and dispersing agent.

Question 2

Advantages of pMDI (4)

Answer 2

Portable, Compact, Easy to Use, Provides Multidose Convenience

Question 3

Which patients pMDIs are preferred for? (2)

Answer 3

Spontaneously breathing patients, and patients who are intubated and undergoing mechanical ventilation

Question 4

Disadvantages of pMDI (3) and limitation (1)

Answer 4

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

Question 5

What does the pMDI administer? (3)

Answer 5

Administer bronchodilators, anticholinergics, and steroids

Question 6

How do the pMDI generate aerosol?

Answer 6

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.

Question 7

How long does aerosol production take?

Answer 7

20 msec

Question 8

What’s a plume and what’s the velocity?

Answer 8

When the liquid suspension is forced out of the pMDI ➔ it forms a plume and propellants vaporizes.
Velocity ➔ approx 15 m/sec

Question 9

What are 2 propellants used and what’s the difference?

Answer 9

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

Question 10

What’s another variation of pMDI and how does it work?

Answer 10

Breath-actuated pMDI ➔ where there’s a trigger that activates when inhaling

Question 11

What’s the advantage and limitation of breath-actuated pMDIs?

Answer 11

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

Question 12

What is the purpose of propellants in a pMDI? And how much does it take up

Answer 12

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

Question 13

What’s the purpose of a Metering Valve?

Answer 13

Metering Valves are responsible for metering/regulation of reproducible volume or dose. The elastomeric valves are responsible for sealing and preventing drug loss/leakage.

Question 14

What’s the purpose of an actuator? (and whats the nickname for it)

Answer 14

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

Question 15

What’s the mechanism of a Soft Mist Inhaler?

Answer 15

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

Question 16

How do you operate a Soft Mist Inhaler?

Answer 16

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

Question 17

What’s priming? and whats the purpose?

Answer 17

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.

Question 18

When and how often should you prime?

Answer 18

When it’s brand new. When it hasn’t been used in awhile (4-6 hours) depending on the label.

Question 19

Factors affecting pMDI performance (4)

Answer 19

Temperature, Nozzle size and Cleanliness, Priming, and Timing of Actuation Intervals

Question 20

How does temperature affect MDI performance?

Answer 20

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

Question 21

How does Nozzle Size and Cleanliness affect MDI performance?

Answer 21

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

Question 22

How does the Timing of Actuation Intervals affect MDI performance? and how long should you wait?

Answer 22

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.

Question 23

What are the 2 primary techniques for pMDIs? And what’s the difference between them?

Answer 23

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

Question 24

What technique would you recommend to a patient?

Answer 24

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.

Question 25

What if the pMDI doesn’t have a dose counter? How would you track the doses remaining?

Answer 25

First, read the label to see how many puffs in the pMDI.
Calculate: Total # of puffs / Total puffs used per day . To see how long the pMDI would last.
Mark the date on a calendar, and refill when there are a few more days left.

Question 26

What are Spacers and Valved Holding Chambers designed to use for?

Answer 26

Designed to reduce oropharyngeal deposition, and the need for hand-breath coordination

Question 27

What makes Spacer different from a VHC?

Answer 27

Spacers are a valveless extension device. The extension/distance allows the plume to expand and propellants to evaporate before it reaches the oropharynx.
The large particles will stick to the spacer walls.
May reduce oral deposition by 90%

Question 28

What makes a VHC different from a Spacer?

Answer 28

VHCs have one of more valves (that act like baffles) preventing aerosol in chamber from being cleared on exhalation.
It produces a finer, slower moving, more ‘respirable’ aerosol
May reduce oral deposition by 99%
Masks can be attached for effective administration

Question 29

How much can the pMDI produce particles? (measurement)

Answer 29

pMDI can produce particles in the respirable range: MMAD 2-6um

Question 30

How much does the Pulmonary Deposition range in adults and larger children?

Answer 30

Pulmonary Deposition ranges between 10-40% (Egans) in adults and larger children with good technique

Question 31

So the Volatile Propellant is combined with surfactant and dispersing agent. What does the dispersing agent do, and what could happen?

Answer 31

Dispersing agent keeps the drug in suspension, it also lubricates the valve mechanism but may cause adverse response: coughing or wheezing

Question 32

What’s the proper technique for Open-mouth? (Step by Step)

Answer 32

1. Warm the device with your hands
2. Prime the device: shake and actuate a couple times
3. Uncap the mouth piece and make sure there’s no debris inside
   * 4. Open mouth wide and have the device 2 or 3 fingers away from your mouth
4. Breathe out normally
5. Start to inhale SLOWLY and then actuate the device while you’re still inhaling until you reached your total lung capacity
6. Hold your breath for at least 10 seconds, or more. Then relax and breathe normally
7. Wait one minute in between puffs. And once finished, recap the mouthpiece

Question 33

What’s the proper technique for Close-mouth? (Step by Step)

Answer 33

1. Warm the device with your hands
2. Prime the device: shake and actuate a couple times
3. Uncap the mouth piece and make sure there’s no debris inside
4. Breathe out normally
   * 5. Place the mouthpiece in between your lips and make sure tongue is out of the way.
5. Start to inhale SLOWLY and then actuate the device while you’re still inhaling until you reached your total lung capacity
6. Hold your breath for at least 10 seconds, or more. Then relax and breathe normally
7. Wait one minute in between puffs. And once finished, recap the mouthpiece

Question 34

What’s the proper technique for using a pMDI with a VHC?(Step by Step)

Answer 34

1. Warm the device with your hands
2. Uncap mouthpiece, check if there’s any debris inside. Prime if necessary
3. Insert the pMDI mouthpiece in the VHC inlet, and place the VHC mouthpiece in between your lips
4. Actuate the device, and normally breathe 3-7 breaths [3 breaths for adults and 7 breaths for infants]
5. Wait for 30-60 seconds before actuations

Question 35

What’s the benefit of Aerospan? (and What’s the generic name for Aerospan?)

Answer 35

Aerospan ➔ Flunisolide Hemihydrate HFA

It has a built-in valveless spacer that improves hand-breath coordination, and had a built-in dose counter