Reviewed and revised 6 August 2015


  • A nebulizer (aerosol generator, atomizer, nebulizing humidifier) emits water in the form of an aerosol mist (water vapor plus particulate water)
  • include small or large volume delivery systems


  • administration of aerosolised particles of water/liquid medication into the airways (e.g. bronchodilators or antibiotics)
  • Ultrasonic nebulisers can deliver inhaled prostacyclin as an alternative therapy to nitric oxide


Large volume systems (generally reusable driver with disposable parts)

  • Jet nebuliser (pneumatically driven, gas-driven, jet, high-pressure, compressed gas)
    — pneumatically driven gas is forced through a small lumen cannula and room air is entrained creating subatmospheric pressure at the top of a capillary tube immersed in water (Venturi effect)
    — water is drawn upwards towards a baffle that breaks the aerosol into fine particles
  • Ultrasonic nebuliser
    — high frequency sound waves generated by an electrically driven ultrasonic resonator vibrate a solution creating an aerosol mist
    — oscillation frequency determines droplet size
    — creates a denser mist than jet nebulisers

Small volume systems (often disposable)

  • Small volume nebuliser
    — use the Venturi effect like the large volume versions; powered commonly by gas supplies; placed in the ventilator circuit
  • Metered dose inhalers
    — via mouthpiece or circuit adapter
  • Spacers
    — via a mouthpiece or device inserted into the ventilator circuit
    — for wet circuits there is an expandable low dead space in-line attachment
    — for dry circuits there is a bulb-like chamber
    — all have an attachment for an MDI


  • Device selection depends on the resources available, preference and perceived utility of the devices


  • Some residual volume may remain in the delivery device (dead volume)
  • variable delivery to the lower airways (depending on delivery system, inspiratory flow rates, tidal volume, end inspiratory pauses)
  • some nebulised drugs can produce bronchospasm
  • if placed too close or accidentally proximal to a HME or filter it can saturate it causing obstruction
  • in-line delivery devices can add dead space and resistance
  • rain out can result from inserting inappropriate devices (e.g. a glass spacer into a wet circuit)
  • loss of PEEP can occur when circuits are broken to insert devices
  • can contribute to hypothermia if not warmed
  • fluid may be a nidus for infection



  • can deliver gas saturated with water without heat


  • cost
  • high flow needed with pneumatic nebulisers
  • potential electrical hazard with ultrasonic nebulisers
  • water deposition (e.g. risk of blocking tubing or water draining into patient)
  • risk of complications (see above)


Important associated concepts:

  • The degree of droplet entry into the respiratory tree depends principally on velocity and particle size. Ultrasonic nebulisers produce the smallest droplets (e.g. 1–10 um)
  • The Venturi effect a the law of fluid dynamics stating that velocity of a fluid must increase when it passes through a constriction to flow
  • The Bernoulli principle is that the Venturi effect occurs there is also a drop in pressure across the constriction in consistent with the laws of conservation of energy

References and Links

Journal articles

  • Dhand R. Inhalation therapy with metered-dose inhalers and dry powder inhalers in mechanically ventilated patients. Respir Care. 2005 Oct;50(10):1331-4; discussion 1344-5. PMID: 16185369.
  • Dhand R. New frontiers in aerosol delivery during mechanical ventilation. Respir Care. 2004 Jun;49(6):666-77. PMID: 15165301.
  • Dhand R. Basic techniques for aerosol delivery during mechanical ventilation. Respir Care. 2004 Jun;49(6):611-22. PMID: 15165296.
  • Rouby JJ, Bouhemad B, Monsel A, Brisson H, Arbelot C, Lu Q; and the Nebulized Antibiotics Study Group. Aerosolized Antibiotics for Ventilator-associated Pneumonia: Lessons from Experimental Studies. Anesthesiology. 2012 Dec;117(6):1364-80. PMID: 23135264.

CCC 700 6

Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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