5.3 Inhalation Devices, Delivery Techniques & Patient Counseling

Inhalation Devices, Delivery Techniques & Patient Counseling

Executive Summary: The clinical efficacy of inhaled pulmonary pharmacotherapy depends entirely on the deposition of active drug molecules within the lower respiratory tract (bronchioles and alveoli). Inhalation aerosol physics dictates that particle size must fall between 1 and 5 microns (Mass Median Aerodynamic Diameter [MMAD]) for optimal pulmonary delivery. Board certified ambulatory care pharmacists must master the operational mechanics, inhalation dynamics, priming rules, and device-patient matching across Pressurized Metered-Dose Inhalers (pMDIs), Dry Powder Inhalers (DPIs), Soft Mist Inhalers (SMIs), and Nebulizers.

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1. Aerosol Physics & Particle Deposition Mechanics

Inhaled medications are categorized by their aerodynamic particle size distribution:

• Particles $>5\;\mu\text{m}$: Possess high inertial momentum. They deposit primarily in the oropharynx, mouth, and upper trachea via inertial impaction, leading to systemic absorption, gastrointestinal swallowing, and local adverse effects (e.g., candidiasis, dysphonia) without clinical pulmonary benefit.
• Particles $1\text{ to }5\;\mu\text{m}$ (The Respirable Fraction): Optimal size range. They travel past the upper airway into the conducting bronchi and peripheral bronchioles, depositing via gravitational sedimentation.
• Particles $<1\;\mu\text{m}$: Remain suspended in the airstream and are largely exhaled during normal tidal breathing without depositing (Brownian diffusion).

+---------------------------------------------------------------------------------------------------------+
|                                 AEROSOL PARTICLE SIZE & DEPOSITION FATE                                  |
+---------------------+-------------------------------+---------------------------------------------------+
| PARTICLE SIZE (MMAD)| PRIMARY DEPOSITION MECHANISM  | CLINICAL OUTCOME / ANATOMIC SITE                  |
+---------------------+-------------------------------+---------------------------------------------------+
| > 5 mcm             | Inertial Impaction            | Oropharynx / Larynx (Systemic uptake, thrush)     |
| 1 to 5 mcm          | Gravitational Sedimentation   | Tracheobronchial & Alveolar airways (TARGET ZONE) |
| < 1 mcm             | Brownian Diffusion            | Exhaled without tissue deposition                 |
+---------------------+-------------------------------+---------------------------------------------------+

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2. Pressurized Metered-Dose Inhalers (pMDIs)

Operational Mechanics & Delivery Dynamics

pMDIs contain micronized drug dissolved or suspended in a chemical propellant (hydrofluoroalkane [HFA]) under pressure. Actuation releases a high-velocity, short-duration plume ($>30\text{ m/s}$, lasting $<0.2\text{ seconds}$):

• Inhalation Technique: Requires a slow, steady, and deep inhalation over 3 to 5 seconds.
• Hand-Breath Coordination: Patient must actuate the canister precisely at the start of inhalation. Firing too early or too late causes the aerosol plume to impact the posterior pharynx.
• Breath-Hold: Patient must hold their breath for up to 10 seconds (or as long as comfortable) to allow gravitational sedimentation of particles.
• Multi-Puff Spacing: If a second puff of a bronchodilator is prescribed, wait 1 minute between actuations to allow propellant equilibrium and airway reopening.

Priming & Maintenance Schedules

pMDIs require priming before initial use or after periods of non-use to ensure a full therapeutic dose:

• ProAir HFA (albuterol): 3 sprays into air if not used for $>14$ days.
• Ventolin HFA (albuterol): 4 sprays into air if not used for $>14$ days or dropped.
• Symbicort (budesonide/formoterol): 2 sprays into air if not used for $>7$ days.
• Flovent HFA (fluticasone propionate): 4 sprays initially; 1 spray if not used for $>7$ days.
• Cleaning: Remove metal canister; rinse plastic actuator under warm running water for 30 seconds once weekly and air dry completely. Never submerge the metal canister in water.

Valved Holding Chambers (VHCs) & Spacers

Spacers and VHCs are hollow plastic extension devices attached to the pMDI mouthpiece:

• Mechanism of Action: Provide distance and a one-way inhalation valve that decelerates the high-speed aerosol plume, allows propellant evaporation, and traps large, non-respirable droplets ($>5\;\mu\text{m}$) on chamber walls.
• Clinical Benefits:
  1. Increases fine-particle respirable lung deposition from 10%–15% up to 25%–30%.
  2. Reduces oropharyngeal impaction by 80% to 90%.
  3. Eliminates the requirement for strict hand-breath coordination.
• Electrostatic Charge & Maintenance: Plastic chambers carry an electrostatic charge that attracts aerosol particles to chamber walls. Patients should use antistatic chambers (e.g., AeroChamber Plus Flow-Vu) or wash chambers once weekly with mild liquid dishwashing detergent and air dry without towel wiping.
• Flow Whistle: Warns the patient if they are inhaling too rapidly (counsel to breathe slower).

Oral Hygiene Counseling for Inhaled Corticosteroids

Oropharyngeal deposition of ICS leads to local immunosuppression and structural vocal cord changes:

• Oral Candidiasis (Thrush): White pseudomembranous plaques on tongue and mucosal surfaces.
• Dysphonia: Hoarseness resulting from steroid-induced vocal cord myopathy.
• Counseling Mandate: After every dose of an ICS or ICS-combination, the patient must rinse their mouth thoroughly with water and spit it out (gargle and expectorate, never swallow). Using a VHC substantially reduces this risk.

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3. Dry Powder Inhalers (DPIs)

Operational Mechanics & Delivery Dynamics

DPIs are breath-actuated devices containing micronized drug formulated as a dry powder, typically blended with larger alpha-lactose monohydrate carrier crystals:

• Inhalation Technique: Requires a quick, forceful, and deep inhalation from the very beginning of the breath.
• Mechanism of Dispersion: The patient's inspiratory effort provides the sole kinetic energy to pull powder through the device's internal resistance, generating turbulent shear forces that de-aggregate the micronized active drug from the heavy lactose carrier.
• Hand-Breath Coordination: Zero coordination required; device fires automatically upon inspiration.
• Spacer Compatibility: NEVER use a spacer or VHC with a DPI (the dry powder cannot be suspended in a chamber and will completely precipitate on the walls).

Subtypes of DPI Devices

+---------------------------------------------------------------------------------------------------------+
|                                    MAJOR DPI DEVICE CATEGORIES                                          |
+-------------------+-------------------------------+-----------------------------------------------------+
| DPI CATEGORY      | REPRESENTATIVE BRAND NAMES    | OPERATIONAL SEQUENCE & MECHANICS                    |
+-------------------+-------------------------------+-----------------------------------------------------+
| Multi-Dose        | Diskus (Advair, Serevent)     | Hold horizontally; slide thumb grip; push lever     |
| Blister Strip     |                               | until it clicks; inhale deeply and forcefully.      |
+-------------------+-------------------------------+-----------------------------------------------------+
| Multi-Dose        | Ellipta (Trelegy, Breo,       | Open cover until click sounds; dose counter         |
| Dual Blister      | Anoro, Incruse, Arnuity)      | decrements; inhale deeply; discard 6 wks post-foil. |
+-------------------+-------------------------------+-----------------------------------------------------+
| Multi-Dose        | Flexhaler / Turbuhaler        | Hold upright; twist base fully one way and then     |
| Reservoir         | (Pulmicort Flexhaler)         | back until click; inhale deeply and forcefully.     |
+-------------------+-------------------------------+-----------------------------------------------------+
| Single-Dose       | HandiHaler (Spiriva)          | Insert capsule into chamber; press side button once |
| Capsule-Based     |                               | to pierce; inhale deeply (capsule rattles); inhale  |
|                   |                               | a 2nd time from same capsule to ensure full dose.   |
+-------------------+-------------------------------+-----------------------------------------------------+
| Single-Dose       | Neohaler / Breezhaler         | Insert capsule; press side buttons simultaneously   |
| Capsule-Based     | (Arcapta, Utibron)            | to pierce; inhale deeply (capsule whirls/rattles).  |
+-------------------+-------------------------------+-----------------------------------------------------+

DPI Golden Counseling Rules

1. Do NOT Shake: Unlike pMDIs, never shake a DPI (shaking can spill or displace the metered powder dose).
2. Never Exhale into the Mouthpiece: Exhaling into the device introduces warm, humid breath, causing powder clumping, microbial growth, and failure of de-aggregation.
3. Moisture Protection: Store in a dry environment (never in a humid bathroom); clean mouthpiece with a dry tissue only—never use water.
4. Severe Milk Protein Allergy: Lactose carriers may contain trace milk proteins. While safe in standard lactose intolerance, DPIs are contraindicated in patients with severe, life-threatening IgE-mediated anaphylaxis to milk protein.

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4. Soft Mist Inhalers (SMIs - Respimat)

Technology & Aerodynamic Properties

The Respimat SMI is a propellant-free mechanical inhaler that uses spring-driven mechanical force to push a metered liquid formulation through a micro-engineered silicon nozzle (Uniblock):

• Slow-Moving Mist: Aerosol exits at a velocity of $\sim 0.8\text{ m/s}$ (approx. $1/10\text{th}$ the speed of a pMDI plume).
• Long Plume Duration: The fine mist cloud lasts for 1.2 to 1.5 seconds (4 to 5 times longer than a pMDI).
• Superior Lung Deposition: Produces a high fine-particle fraction resulting in $>50\%$ lung deposition with minimal oropharyngeal impaction, completely independent of the patient's inspiratory effort.

Operational Technique: The TOP Mnemonic

1. T = TURN: With cap closed, turn the clear base in the direction of the red arrows until it clicks (half-turn).
2. O = OPEN: Flip the protective safety cap completely open.
3. P = PRESS: Place lips around mouthpiece, press the dose-release button while taking a slow, deep breath in; hold breath for up to 10 seconds.

Priming & Setup

• Cartridge Loading: Push the narrow end of the cartridge into the inhaler firmly against a hard, flat surface until it snaps into place. Replace the clear base.
• Initial Priming: Turn, open, and press the dose-release button facing the ground until a cloud is visible, then repeat 3 additional times.
• Missed Use Priming: If not used for $>3$ days, actuate 1 spray toward the ground. If not used for $>21$ days, repeat the full 4-spray initial priming sequence.

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5. Peak Inspiratory Flow Rate (PIFR) Assessment & Clinical Device Matching

The Critical Role of PIFR in Device Selection

DPIs rely entirely on the patient's inspiratory muscle effort to de-aggregate the dry powder. Peak Inspiratory Flow Rate (PIFR) measures the maximum airflow generated during forced inspiration through the internal resistance of a specific inhaler:

• Optimal PIFR Threshold: $\ge 60\text{ L/min}$ against device internal resistance (or $\ge 30\text{ L/min}$ for high-resistance DPIs e.g., HandiHaler).
• Suboptimal PIFR ($<60\text{ L/min}$): Common in elderly patients, severe COPD ($ ext{FEV}_1 < 50\%$), female patients, and during acute exacerbations. Patients with suboptimal PIFR cannot disperse dry powder into respirable droplets, leading to clinical treatment failure despite reported adherence.
• Assessment Tool: The In-Check DIAL device measures a patient's PIFR against simulated resistance dial settings matching specific inhalers.

Clinical Device Selection Matrix

+---------------------------------------------------------------------------------------------------------+
|                               PATIENT PROFILING & DEVICE MATCHING ALGORITHM                             |
+------------------------------------+-----------------------------+--------------------------------------+
| PATIENT CLINICAL CHARACTERISTICS   | CONTRAINDICATED / SUBOPTIMAL| PREFERRED INHALATION DEVICE PLATFORM |
+------------------------------------+-----------------------------+--------------------------------------+
| Suboptimal PIFR (<60 L/min)        | DPIs (Diskus, Ellipta,      | pMDI + Valved Holding Chamber,       |
| (Severe COPD, Elderly, Frail)      | HandiHaler, Flexhaler)      | SMI (Respimat), or Nebulizer         |
+------------------------------------+-----------------------------+--------------------------------------+
| Poor Hand-Breath Coordination      | Standalone pMDI (no spacer) | DPI, SMI (Respimat),                 |
| (Arthritis, Tremors, Stroke, Peds) |                             | pMDI + Valved Holding Chamber        |
+------------------------------------+-----------------------------+--------------------------------------+
| Cognitive Impairment / Dementia    | Complex multi-step DPIs     | Jet / Vibrating Mesh Nebulizer       |
| (Cannot follow multi-step sequence)|                             | with mouthpiece or facemask          |
+------------------------------------+-----------------------------+--------------------------------------+
| High Inspiratory Flow (PIFR >= 60) | None                        | DPI, SMI (Respimat), or              |
| with Good Coordination             |                             | pMDI + Valved Holding Chamber        |
+------------------------------------+-----------------------------+--------------------------------------+

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6. Comprehensive Inhalation Device Feature Comparison