Ultrasonic nebulizers are devices that produce a fine mist aerosol. The USN is used for humidification of the airways to help mobilize secretions and to deliver solutions. The ultrasonic nebulizer basically consists of a:

1. radio frequency generator – produces a radio signal to the transducer.
2. a piezoelectric transducer – converts electricity to sound waves.
3. a reservoir or couplant chamber containing water – smaller nebulizers may not have a couplant chamber.
4. a solution cup or nebulizer chamber.
5. a blower fan.

The ultrasonic nebulizer uses a piezoelectric transducer located in the couplant chamber of the unit. When electricity passes through the transducer it produces high – frequency vibrations that are focused on the diaphragm of the water reservoir. The vibrations are transferred through the water of the couplant chamber (or reservoir) to the solution cup or (nebulizer chamber) by a membrane. The water in the couplant chamber keeps the transducer cool during operation as well as transmit vibrations.

The vibrations hit the solution cup or nebulizer chamber that is located within the couplant chamber and breaks the water or medication into small particles that are usually within the 0.5 to 3 micron sized range. The frequency of the ultrasonic nebulizer determines the size of the particles. Most models are preset at the factory at approximately 1.35 megacycles/sec.

The amplitude of the ultrasonic controls the volume of the aerosol output and is adjustable by the therapist. Output ranges between 3 to 6 ml/min, being much higher than the conventional jet nebulizer. The aerosol density (number of particles per unit volume) is inversely proportional to the flow. Suggested settings for using the ultrasonic for sputum induction should be a high amplitude with a low flow. This will result in a high density output. Suggested settings for mobilization of secretions will be a high amplitude with a high flow to maximize the volume of aerosol delivered per minute.

A blower is attached to deliver the mist to the patient through large-bore tubing and may deliver 20 to 30 L/min of air to the nebulizer cup. The ultrasonic has the highest output range of aqueous solution without being heated of all the nebulizers. A constant level of solution is maintained in the nebulizer chamber through a continuous feed attachment.

It is recommended by most that ultrasonic nebulizers should not be used for delivering pharmacologically active medications like bronchodilators, mucolytics, and antibiotics. These medications may not nebulize uniformly and may break down and be rendered ineffective during the process.

>The advantages of using an ultrasonic nebulizer are that the aerosol delivery is not dependent on the airflow but on the amplitude setting. Ultrasonics produce 100% relative humidity and can be run for extended periods of time when on a continuous feed system. They are quiet to operate, produce a dense and uniform mist, and are easily cleaned.

(Photo: Ultra-Neb 99 Ultrasonic Nebulizer. Provides Continuous Humidification w/Optional 3 liter bottle. Applications include humidification, medication nebulization, and respiratory disease diagnosis.)

Hazards of ultrasonic nebulizer therapy include:

1. Overhydration
2. Nosocomial infection transmission
3. Bronchospasms
4. Swelling of secretions and being unable to cough them out
5. Electrical hazards
6. Some devices may interfere with cardiac pacemakers
7. Water collecting in the tubing obstructing the flow

Troubleshooting and using the ultrasonic nebulizer:

1. Check for adequate fluid levels in the couplant chamber if mist is not sufficient.
2. Maintain adequate levels in the solution cup. If the levels are either too high or too low no aerosol will be produced.
3. Increase the amplitude (volume) control or check the filter for obstruction if mist is not sufficient.
4. Water should be drained from the large-bore tubing to prevent changes in the flow and FI02.
5. A kinked tubing or a float not working properly on the continuous water feed system will affect the aerosol output also.
6. Low flow rates will produce smaller particles and a higher mist density than higher flow rates.
7. Units should be cleaned according to the manufacturer's recommendation.
8. Appropriate disinfection should be done at least every 6 days.
9. Water should be discarded from the reservoir periodically between cleanings.