Nebulizers

Reviewed and revised 6 August 2015

OVERVIEW

• 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

USE

• 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

DESCRIPTION

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

METHOD OF INSERTION/ USE

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

COMPLICATIONS

• 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

PROS AND CONS

Advantages

• can deliver gas saturated with water without heat

Disadvantages

• 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)

OTHER INFORMATION

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.