Nebulisers: uses and abuses

Metered dose inhalers for bronchodilator delivery in intubated, mechanically ventilated patients

We determined the relative efficacy of two bronchodilator aerosol delivery methods in 18 intubated mechanically ventilated patients with airways obstruction. Two treatment arms, consisting of albuterol 270 micrograms (three puffs) from a metered dose inhaler and albuterol 2.5 mg from a saline solution nebulized with an updraft inhaler, were compared in a single blind, randomized crossover design. Pulmonary function was evaluated using an interrupter technique. Changes in passive expiratory flow at respiratory system recoil pressures between 6 and 10 cm H2O provided the therapeutic endpoints. Paired measurements were made before and 30 minutes after drug delivery. The MDI and NEB resulted in similar improvements in iso-recoil flow (mean increase for both groups = 0.1 L/s). Treatment sequence, severity of obstruction, and bronchodilator responsiveness had no effect on relative efficacy. Albuterol caused a small but significant increase in heart rate that was similar following both delivery methods. We conclude that bronchodilator aerosol delivery with metered dose inhalers provides a viable alternative to nebulizer therapy in intubated mechanically ventilated patients and may result in a cost savings to hospitals and patients.

In vitro comparison of DeVilbiss jet and ultrasonic nebulizers

Output, droplet size (by laser instrument), and nebulization time have been compared in vitro for eight individual ultrasonic nebulizers (DeVilbiss Pulmosonic) and eight individual jet nebulizers (DeVilbiss 646), the latter operated by compressed air at flows of 6 and 12 L/min. A solution of hypertonic (7 percent) saline was nebulized. The ultrasonic nebulizer retained a higher "dead" volume of solution on completion of nebulization (p less than 0.05), but the increase in saline concentration was less marked than for the jet (p less than 0.01). The mass of NaCl released as aerosol was similar for the ultrasonic and for the jet at 6 L/min but was increased for the jet at 12 L/min (p less than 0.05). There was a fivefold interindividual variation in output for the ultrasonic. Droplet mass median diameters for the ultrasonic (mean 5.4 micron) were slightly lower than those for the jet at 6 L/min (mean 6.0 micron, p less than 0.05) but were higher than those for the jet at 12 L/min (mean 3.7 micron, p less than 0.01). The ultrasonic emitted virtually no droplets less than 2 micron diameter and may be unsuitable for applications requiring high yields of fine particles for delivery to the peripheral lung regions.