Aerosol
Suspension of solid or liquid particles in gas.
Medical aerosols
Generated with devices that physically disperse matter into small particles and suspend them into gas.
Atomizers
Jet and capillary.
Nebulizers
Jet, capillary, and baffle.
Inhalers
Propellant.
Aerosol output
- Mass of fluid or drug contained in aerosol
- Output rate is mass of aerosol generated per unit of time
Emitted dose
Mass of drug leaving mouthpiece as aerosol.
Gravimetric analysis
Measures aerosol weight.
Assay
Measures quantity of drug.
Particle size
Depends on three factors:
1. Substance being nebulized.
2. Method used.
3. Environmental conditions.
Geometric standard deviation (GSD)
Variability of particle sizes.
- Greater the GSD, wider range of particle sizes and more heterodisperse aerosols
Heterodisperse aerosols
Aerosols with particles of different sizes.
Monodisperse aerosols
Aerosols with particles of similar sizes.
Deposition
- Only fraction of emitted aerosol (emitted dose) will be inhaled
- Only fraction of inhaled aerosol (respirable dose) is deposited in lungs
Inhaled mass
Amount of drug inhaled.
Respirable mass
Portion of inhaled mass that can reach lower airways.
Deposition influences
- Inspiratory flow rate
- Flow pattern
- Respiratory rate
- Inhaled volume
- I:E ratio
- Breath-holding
Deposition key-mechanisms
- Inertial impaction
- Gravimetric sedimentation
- Brownian diffusion
Inertial impaction
- Occurs when aerosol in motion collides with and are deposited on surface
- Primary deposition mechanism for larger particles (>5 um)
- Greater mass and velocity of moving object, then greater inertia and greater tendency of that object to continue movin
Sedimentation
- Occurs when aerosol particles settle out of suspension and are deposited due to gravity
- Represents primary mechanisms for deposition of small particles (1-5 um)
- Greater mass of particle, the faster it settles
Breath-holding after inhalation of aerosol
Increases sedimentation and distribution across lungs.
Brownian diffusion
- Primary deposition mechanism for very small particles (<3 um) deep within lung
- Particles between 1 and 0.5 um have very low mass and are so stable that most remain in suspension and are exhaled back into environment
- Particles >0.5 um have greater re
Aging
Process by which aerosol suspension changes over time.
Aerosol aging
Depends on:
- Composition of aerosol
- Initial size of its particles
- Time in suspension
- Ambient condition
Aerosol therapy hazards
Primary hazard of aerosol drug therapy is adverse reactions to medication.
Other possible hazards include:
- Airway reactivity
- Pulmonary and systemic effects of bland aerosols
- Drug concentration changes during nebulization
- Eye irritation
Pressurized metered-dose inhalers (pMDIs)
Pressurized canister containing prescribed drug in volatile propellant combined with surfactant and dispersing agent.
- Most commonly prescribed method of aerosol therapy
- Portable, compact, and easy to use
- Provide multidose convenience
- Has serious l
Breath-actuated pMDIs
- Incorporates trigger activated during inhalation
- Reduces need for patient/caregiver to coordinate MDI actuation with inhalation
Aerocount inhaler
- Flow-triggered
- Eliminates the need for hand-breath coordination
Easihaler and Tempo
Breath-actuated
Factors affecting pMDI performance
- Temperature
- Nozzle size and cleanliness
- Priming
- Timing of actuation intervals
Aerosol delivery characteristics
- pMDIs can produce particles in respirable range (MMAD 2-6 um)
- 80% of aerosol deposits in oropharynx
- Pulmonary deposition ranges between 10-20% in adults and larger children
pMDI use
- Should be actuated at beginning of inspiration with mouthpiece held 4 cm in front of open mouth
Open-mouth technique
Concerns include:
- Ipratropium bromide administration along with poor coordination can result in drug being sprayed into eyes
- Anticholinergic agents have been associated with increased ocular pressure
- Steroid pMDIs can increase incidence of opportuni
Spacers
- Simple, valveless extension device that adds distance between pMDI outlet and patient's mouth
- Reduces oropharyngeal deposition and need for hand-breath coordination
Holding chambers
- Incorporates one or more valves that prevent aerosol in chamber from being cleared on exhalation
- Provides less oropharyngeal deposition, higher respirable drug dosages, and better protection from poor hand-breath coordination than simple spacers
Dry powder inhalers (DPIs)
- Breath-actuated dosing system
- Patient creates aerosol by drawing air through dose of finely milled drug powder
- Dispersion of powder into respirable particles depends on creation of turbulent flow in inhaler
- Do not use propellants and do not requir
Unit-dose DPI
Aerolizer and handihaler dispense individual doses of drug from punctured gelatin capsules.
Multiple-dose DPI
Diskhaler contains case of four or eight individual blister packets of medication on disk inserted into inhaler.
Multiple dose drug reservoir DPI
Twisthaler, Flexhaler, and Diskus are preloaded with quantity of pure drug sufficient for dispensing 120 doses of medication.
Factors affecting DPI performance and drug delivery
- Intrinsic resistance and inspiratory flow rate
- Exposure to humidity and moisture
- Patient's inspiratory flow ability
DPI use
Should not be used by infants, small children, those who cannot follow instructions, and patients with severe airway obstruction.
Pneumatic (jet) nebulizers
Most nebulizers are powered by high-pressure oxygen or air provided by portable compressor, compressed gas cylinder, or 50-psi gas outlet.
Factors affecting nebulizer performance
- Nebulizer design
- Gas pressure/flow
- Gas density
- Medication characteristics
Small volume nebulizers (SVN)
Four categories:
1. Continuous nebulizer with simple reservoir.
2. Continuous nebulizer with collection reservoir bag.
3. Breath-enhanced (BE).
4. Breath-actuated nebulizer (BAN).
Continuous nebulizer with simple reservoir
May increase inhaled dose by 5-10% or increase inhaled dose from 10-11% with 6" piece of reservoir tube.
Continuous nebulizer with collection reservoir bag
- Bag reservoirs hold aerosol generated during exhalation
- Allows small particles to remain in suspension for inhalation with next breath while larger particles rain out
- Attributed to 30-50% increase in inhaled dose
Breath-enhanced (BE)
Generate aerosol continuously, utilizing system of vents and one-way valves.
Breath-actuated nebulizer (BAN)
Can increase inhaled aerosol mass by 3-4 fold over conventional continuous nebulizers.
SVN technique
- Slow inspiratory flow optimizes SVN aerosol deposition
- Selection of delivery method is based on patient ability, preference, and comfort
Large volume nebulizers
- Particularly useful when traditional dosing strategies for patients with bronchospasm are not affective
Special LVNs
Provide CBT.
- HEART
- Westmed
- HOPE
- Small-particle aerosol generator (SPAG)
Small-particle aerosol generator (SPAG)
- Designed specifically for administration of ribavirin
- Incorporates drying chamber with its own flow control to produce stable aerosol
- Concerns include caregiver exposure to drug and drug precipitation can jam breathing valves in mechanical ventilato
Hand-bulb atomizers and spray pumps
- Used to administer sympathomimetric, anticholinergic, antiinflamatory, and anesthetic aerosols to upper airway
- Deposition with hand-bulb atomizer applied to nose occurs mostly in anterior nasal passages with clearance to nasopharynx
- Spray pump produ
Ultrasonic nebulizers (USNs)
- Uses piezoelectric crystal to produce aerosol
- Crystal converts electrical energy into high-frequency vibrations to produce aerosol
- Capable of higher aerosol outputs (0.2-1.0 ml/min) and higher aerosol densities than are conventional jet nebulizers
-
Large-volume USN
- Incorporates air blowers to carry mist to patient
- Primarily used for deliver of bland aerosol therapy or sputum induction
- Low flow through nebulizer is associated with smaller particles and higher mist density
- Temperature of solution placed in USN
Small-volume USN
- Can be used to deliver bronchodilators, antibiotics, and anti-inflammatory agents
- Can be used to administer undiluted bronchodilator to patient with sever bronchospasm
- Patient's inspiratory flow draws aerosol from nebulizer into lung
Vibrating mesh (VB) nebulizer (Active)
- Utlizes dome-shaped aperture plated containing more than 1000 funnel-shaped apertures
- Exit velocity of aerosol is low (<4 m/sec)
- Particle size can range between 2-3 um (MMAD), varying with exit diameter of apertures
- Can nebulize single drops as sm
Vibrating mesh (VB) nebulizer (Passive)
- Utilizes mesh separated from ultrasonic horn by liquid to be nebulized
- Residual drug volume ranges from 0.1-0.4 ml
- Care should be exercised when transitioning to these devices
Smart nebulizers
Akita (Activaero):
- Controls inspiratory flow to keep it slow (12-15 lpm) and reduce impaction loss of aerosols in upper airways
- Patient pulmonary function is stored on smart card programmed to tell device when to generate aerosol during inhalation
Special medication delivery issues for infants and children
- Smaller airway diameter than adults
- Breathing rate is faster
- Nose breathing filters out large particles
- Lower minute volumes
- Patient cooperation and ability varies with age and developmental ability
- Should never be delivered during crying (red
Blow-by technique
- Used if patient cannot tolerate mask treatment
- Practitioner directs aerosol from nebulizer toward patient's nose and mouth distance of several inches from face
Components of patient assessment
- Patient interviewing
- Observation
- Measurement of vital signs
- Auscultation
- Blood gas analysis
- Oximetry
Conduct dose
Response filtration to determine best dosage for patients with moderate obstruction.
Off-label use
- Use of drugs that have not been approved and viable alternative exists
- Should always be backed up by appropriate departmental or institutional policies and procedures
CBT
- Used to treat severe asthma
- Doses ranging from 5-20 mg/hour have proved to be safe for adult and pediatric patients with severe asthma
- Patient carefully assessed every 30 minutes fro first 2 hours; then hourly
- Positive response indicated by increa
Aerosol administration to mechnically ventilated patients
- SVN
- USN
- VM
- pMDI
- DPI
Assessing response to bronchodilator
- Measure change in difference between peak and plateau pressures
- Drop in peak = bronchodilator is effective
- Drop in plateau = bronchodilator is effective
Non-invasive ventilation
- Administered with standard and bi-level ventilators
- Bi-level ventilators often utlize flow turbine, with fixed valve or leak in circuit which permits excess flow to vent to atmosphere
High-flow nasal oxygen
- Type and location of nebulizer used with high-flow nasal oxygen, cannula size, respiratory pattern, and oxygen flow affect inhaled dose
Intrapulmonary percussive ventilation
- Provides high-frequency oscillation of airway while administering aerosol particles
- Aerosol generator should be placed in circuit as close to patient's airway
High-frequency oscillatory ventilation
Administration of albuterol sulfate via VM placed between ventilator circuit and patient airway delivers.