Guide — Aerosol Therapy & Pharmacology
Aerosol Drug Delivery
Getting a drug into the lung is a physics problem before it is a pharmacology one. This guide covers respirable particle size, how aerosols deposit, and the device-by-device technique an RT must teach and verify — then how to match the right device to the patient in front of you.
10 min read · Aerosol Therapy & Pharmacology
Written by Apex Respiratory Editorial Team
Educational use only. This material supports respiratory therapy education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional protocols, or physician orders. Always follow facility policies and current provider orders, and verify calculations independently before clinical use.
Overview
Aerosol therapy delivers a drug directly to the airway, but only the fraction of the dose carried on respirable particles actually reaches the lower airways. Particle size governs where an aerosol lands: the respirable range is roughly 1–5 µm MMAD. Particles larger than 5 µm deposit in the oropharynx by inertial impaction, and very small particles below 1 µm are largely exhaled before they settle.
The device, the patient’s technique, and the patient’s ability all decide how much of that respirable fraction lands where it should. The RT’s job is to choose a device the patient can actually use, teach and verify the technique it demands, and then assess whether the therapy worked.
Key Concepts
Three mechanisms move particles out of the airstream and onto the airway: inertial impaction (large particles at high flow, the cause of oropharyngeal deposition), gravitational sedimentation (mid-sized particles settling out, favored by a breath-hold), and diffusion (the smallest particles, by Brownian motion). The device determines which mechanism dominates and what the patient must do to make it work.
| Device | Inhalation Technique | Best For |
|---|---|---|
| pMDI | Slow deep breath; actuate at the start of inhalation; 10-second breath-hold | Cooperative patients who can coordinate actuation with a slow breath |
| pMDI + spacer / valved holding chamber | Slow deep breath after actuation (or tidal breathing with a mask) | Children, acute distress, and any inhaled corticosteroid |
| DPI (dry powder inhaler) | A fast, forceful, deep breath to de-aggregate the powder | Patients who can generate > 60 L/min of inspiratory flow |
| SVN (small-volume nebulizer) | Normal tidal breathing | Acute distress, high doses, or a patient who cannot coordinate |
| SMI (soft mist inhaler) | A slow deep breath of the slow-moving mist | Maintenance with less coordination than a pMDI |
Assessment & Findings
- Confirm adequate inspiratory flow for a DPI. Before reaching for a dry-powder inhaler, verify the patient can generate the fast, forceful breath it requires — roughly 60 L/min. A patient who cannot will not de-aggregate the powder.
- Watch for poor technique. The common failures are no breath-hold and an actuation-inhalation mismatch with a pMDI — firing the canister before or after the breath rather than at its start. These quietly waste the dose.
- Reassess after therapy. Re-evaluate breath sounds and work of breathing after a treatment. The point of delivery is the clinical response — assessing it tells you whether the drug landed and worked.
RT Priorities / Interventions
- Match the device to the patient’s ability. Acute distress or poor coordination points to a nebulizer or a pMDI with a spacer; a patient who cannot generate inspiratory flow is not a candidate for a DPI. The best device on paper is useless if the patient cannot use it.
- Teach and verify technique. Demonstrate the maneuver, then watch the patient perform it. Technique drifts, so verify it — not just on the first encounter.
- Use a spacer with every ICS. A spacer or valved holding chamber improves respirable delivery and cuts the oropharyngeal deposition that drives thrush and dysphonia — it belongs with every inhaled corticosteroid.
- Assess the response. Close the loop: confirm the therapy improved the gas exchange and mechanics it was meant to, and rethink the device or drug if it did not.
Common Pitfalls
- Prescribing a DPI to a patient who cannot generate enough inspiratory flow. The most common aerosol mismatch — the powder never de-aggregates and the dose is lost in the mouth.
- A fast inhalation with a pMDI. A quick, hard breath drives the aerosol into the oropharynx by inertial impaction. A pMDI wants a slow, controlled breath.
- Skipping the breath-hold. The 10-second hold lets mid-sized particles sediment onto the airway. Exhaling immediately blows much of the dose back out.
- No spacer with an ICS. Omitting the spacer raises oropharyngeal deposition and the risk of thrush while lowering the respirable dose.
- Not shaking a suspension pMDI. A suspension separates between actuations; failing to shake it delivers an inconsistent, often sub-therapeutic dose.
Board Exam Pearls
- The respirable range is 1–5 µm — the single most tested number in aerosol therapy.
- A DPI needs a fast, forceful breath; a pMDI needs a slow, coordinated breath with a breath-hold. If a stem swaps those, it is the wrong answer.
- A spacer improves pMDI delivery and cuts oropharyngeal deposition — the reason it pairs with every ICS.
- Nebulizers use normal tidal breathing and suit acute distress or a patient who cannot coordinate.
FAQ
What particle size reaches the lower airways?
The respirable range is roughly 1–5 µm mass median aerodynamic diameter (MMAD). Particles larger than 5 µm deposit in the oropharynx by inertial impaction rather than reaching the lung, and very small particles below 1 µm are largely exhaled before they can deposit. Engineering an aerosol into that 1–5 µm window is what allows a drug to reach and act on the lower airways.
Why does a DPI require a fast, forceful breath?
A dry-powder inhaler is breath-actuated and uses the patient's own inspiratory effort to disperse the drug. A fast, forceful, deep breath generates the turbulent energy needed to de-aggregate the powder into respirable particles. Without an inspiratory flow of roughly 60 L/min or more, the powder stays clumped and large, deposits in the mouth and throat, and little reaches the lung — which is why a DPI is the wrong choice in severe distress or for a patient who cannot generate that flow.
How does a spacer or valved holding chamber help?
A spacer or valved holding chamber lets the propellant evaporate and the largest, fastest particles drop out before the aerosol is inhaled, so more of the dose is in the respirable range and far less impacts the oropharynx. It also removes the need to precisely time actuation with inhalation — the patient can take a slow deep breath after actuation, or tidal-breathe through a mask — which is why a spacer should be used with every inhaled corticosteroid and is invaluable for children and patients in acute distress.
Which device suits a patient in acute distress who cannot coordinate?
A small-volume nebulizer or a pMDI with a spacer. Both work with normal tidal breathing and demand no precise hand-breath coordination, so they suit a patient who is acutely short of breath or cannot follow a slow-deep-breath-and-hold maneuver. A DPI is the wrong choice here because it depends on a fast, forceful inspiratory effort the distressed patient cannot reliably produce.
Put it to work
An aerosolized drug is only as good as the gas exchange it improves. Run an arterial blood gas through the interpreter to assess the oxygenation and ventilation a therapy is meant to move.
Open the ABG Interpreter →Related Resources
Sources
- Gardenhire DS. Rau's Respiratory Care Pharmacology. 10th ed. Elsevier; 2019.
- Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021. Aerosol drug therapy chapter.