NEBULIZERS

• Aerosols are small particles of liquids or solids suspended in a carrying gas
• Medical aerosols can be produced by a nebulizer
• The therapeutic efficacy of the aerosol is dependent on the liquid or solid’s ability to remain in suspension and the depth reached by the aerosol on inhalation, and is dependent on its stability. These are both determined by the particle size.
• For liquid medication to enter the alveolithe droplets must be smaller than the diameter of the terminal bronchioles and fall within the size range of 0.005 µm to 50 µm in diameter.
• For droplet sizes below 5 µm, gravity exerts a negligible effect.
• Particles or droplets in the range 5 to 10 µm tend to deposit in the upper airways,with material below 5 µm penetrating further into the lungs.
• Below 3 µm, the droplets enter the alveoli and become therapeutically beneficial.
• Droplets below 1 µm are ideal; but if significantly smaller than this, the particles will be exhaled without having a therapeutic effect.
• The temperature for an aerosol generated by a nebulizer must not exceed 37°C and the process must not alter the structure of the medication being carried.
• This is the essential difference between vaporizers that generate a vapour and nebulizers that produce liquid droplets.
• Jet or gas driven nebulizer (atomizers)
• A high flow of gas is driven over a capillary tube that is immersed into the fluid to be nebulized. The high pressure air driven through the small orifice, generates negative pressure as a result of the Venturi effect. These nebulizers are simple and low cost, but small variations in gas flow rate can result in inconsistent delivery of aerosol to the patient.
• Ultrasound driven nebulizer
• The ultrasound nebulizer incorporates a ceramic piezoelectric transducer that changes electrical energy into mechanical energy (pressure oscillations). The transducer sits at the bottom of the chamber and vibrates at a frequency of 1.5 MHz. The vibrations are transmitted through the water. The diaphragm is in contact with the solution to be nebulized and violently shakes the solution into particles. At low frequencies, larger particles are produced, but at higher frequencies, a fine mist is generated
• Ultrasonic nebulizers tend to produce a more consistent particle size than jet nebulizers and, as a result, produce a much greater deposition into the lungs.
• But long-term use of ultrasonic nebulization might inadvertently affect surface tension stability in the alveoli