Inhalation Devices in COPD/Asthma: Modes, Merits, and Demerits

Introduction

• Smaller drug doses required
• More rapid onset of therapeutic action
• Decreased systemic adverse effects compared to oral/parenteral routes

1. Pressurized Metered-Dose Inhaler (pMDI)

Mechanism

Merits

• Compact and portable - fits in a pocket; suitable for emergency use
• Multi-dose - 100-200 doses per canister
• Quick treatment time - delivery in seconds
• Drug in sealed canister - protected from humidity and contamination
• Inexpensive - most cost-effective inhaler
• Dose and particle size independent of inhalation maneuver (unlike DPI)
• Available for most drug classes - bronchodilators, corticosteroids, combinations
• No inspiratory flow requirement - can be used even in severe obstruction

Demerits

• High oropharyngeal deposition (~80% of dose) due to high spray velocity
• Hand-mouth coordination required - patient must actuate simultaneously with inspiration (many fail this, especially elderly, children, arthritic patients)
• "Cold Freon" effect - cold spray can cause reflex breath-holding, worsening deposition
• Propellant required - HFA propellants contribute to greenhouse gas emissions
• Difficult to assess when canister is empty (no integrated dose counter in many devices)
• Requires priming if not used for a period
• Shaking required before each use (suspension formulations)

Technique (Critical for Exams)

1. Remove cap, shake well; 2. Exhale to comfortable volume; 3. Actuate as you breathe in slowly (like sipping hot soup); 4. Inhale to near total lung capacity; 5. Hold breath 10 seconds; 6. Wait 1 minute before second puff.

2. Spacer / Holding Chamber (Accessory Device with pMDI)

Mechanism

Merits

• Eliminates need for hand-mouth coordination - ideal for elderly, children, those with poor technique
• Reduces oropharyngeal deposition by 10-fold - larger particles settle in spacer rather than throat
• Reduces risk of oral candidiasis with inhaled corticosteroids
• Reduces systemic absorption - less drug swallowed
• Equivalent efficacy to nebulizer in acute asthma (studies show pMDI + spacer = nebulizer for acute bronchodilation)
• Audible/visible feedback - some chambers whistle if inhalation is too fast

Demerits

• Bulky and less portable - not convenient to carry everywhere
• Requires regular cleaning - electrostatic charge builds on plastic spacers, reducing drug delivery (metal/anti-static spacers preferred)
• Drug may adhere to spacer walls (antistatic priming with detergent helps)
• Additional cost over pMDI alone
• Compatibility issues - not all spacers work with all pMDIs

3. Dry Powder Inhaler (DPI)

Mechanism

• Single-dose (Handihaler, Breezhaler) - capsule/blister loaded before each use
• Multi-dose reservoir (Turbuhaler - 200 doses, Twisthaler)
• Multi-dose blister (Diskus/Accuhaler - 60 doses, Ellipta - 30 doses)

Merits

• Compact and portable - similar to pMDI
• Quick treatment time
• Breath-actuated - removes need for hand-mouth coordination (patient simply inhales)
• No propellant - environmentally friendly; no cold Freon effect
• Dose counter available in most devices (Diskus, Turbuhaler)
• Simpler technique for most patients vs. pMDI
• Drug protected within capsule/blister until used

Demerits

• Adequate inspiratory flow required (minimum 30-60 L/min depending on device) - cannot be used in:
  • Severe acute exacerbations
  • Very young children (<5 years)
  • Patients with very low FEV1/severe COPD
• Humidity sensitive - moisture causes powder clumping and reduced fine particle fraction; cannot be stored in bathrooms/humid climates
• High pharyngeal deposition possible if flow is too high
• Device-specific technique - each DPI has different loading/inhalation steps; patient education needed
• Cannot be used with spacer
• More expensive than pMDI in most markets

Key DPI Devices for Exams:

4. Soft Mist Inhaler (SMI) - Respimat

Mechanism

Merits

• No propellant - environmentally friendly
• Slow aerosol velocity (~0.8 m/s vs. ~8 m/s for pMDI) - markedly reduced oropharyngeal deposition
• High fine particle fraction - higher lung deposition (~52%) than pMDI (~20%)
• Less hand-mouth coordination needed - aerosol cloud lasts ~1.5 seconds (vs. 0.15 sec for pMDI), allowing easier coordination
• No inspiratory flow dependence - suitable for severe COPD patients
• Moisture-resistant - generated from solution, not powder; suitable for humid climates
• Dose counter integrated
• Consistent dosing regardless of canister filling level

Demerits

• Limited drug availability - currently only tiotropium, olodaterol, ipratropium/salbutamol combinations
• More complex preparation - requires loading cartridge and priming
• Relatively expensive
• Rotation required for dose preparation (quarter turn of base before each use)
• Less widely available than pMDI and DPI

5. Nebulizer

Types:

• Jet nebulizer: Compressed air/oxygen drives liquid drug through narrow orifice, creating aerosol. Most common.
• Ultrasonic nebulizer: High-frequency sound waves vibrate drug solution to create aerosol.
• Mesh nebulizer: Liquid forced through a mesh with multiple apertures; produces fine, low-velocity aerosol; portable.

Mechanism

Merits

• No coordination or inspiratory effort required - ideal for:
  • Severe acute exacerbations
  • Very young children (with mask - from birth)
  • Elderly, confused, or disabled patients
  • Mechanically ventilated patients (inline nebulizers)
• Can deliver large doses of medication
• Can deliver combination drugs simultaneously (salbutamol + ipratropium in one cup)
• No propellant
• Continuous therapy possible in acute severe asthma
• Can be used with supplemental oxygen (jet nebulizer driven by oxygen)

Demerits

• Bulky and not portable (jet nebulizers require electricity/compressor; mesh nebulizers are newer and more portable)
• Long treatment time - 10-20 minutes per treatment
• Higher cost - device plus ongoing maintenance
• Requires regular cleaning and sterilization - risk of bacterial contamination if not cleaned properly
• Significant drug wastage - only 10-15% of dose reaches lungs; remainder deposited in device/atmosphere
• Loud - compressor noise
• Requires medical/technical setup at home

Comparison Table: Summary for Exams

Factors Governing Device Selection (ACCP Guidelines)

1. Clinical condition and disease severity
2. Availability of the specific drug in the chosen device
3. Patient's ability to use the device correctly
4. Use of the same device type for all inhaled drugs (simplifies technique)
5. Setting (inpatient vs. outpatient)
6. Cost and insurance coverage
7. Age: <5 years - pMDI + spacer with mask or nebulizer; 5-12 years - pMDI + spacer or DPI; >12 years - any device if technique adequate

High-Yield Exam Points

• Spacer = pMDI enhancer: Converts coordination-dependent pMDI to near-breath-actuated device; reduces oral candidiasis with ICS
• DPI requires minimum inspiratory flow - contraindicated in acute severe asthma and very young children
• SMI (Respimat) has highest lung deposition and is propellant-free
• Nebulizer = only option for mechanically ventilated patients and neonates
• pMDI + spacer = nebulizer in efficacy for acute asthma treatment (multiple RCTs and meta-analyses)
• Critical errors: For pMDI - actuation before inhalation; For DPI - insufficient inspiratory effort (most common, affects 32-38% of DPI users); both lead to uncontrolled asthma and increased exacerbations
• Turbuhaler requires highest inspiratory flow (~60 L/min); Diskus requires least (~30 L/min) among popular DPIs
• Inhaler errors (299 definitions in literature) are common in both patients AND healthcare workers - training is essential