ABSTRACr The size distribution of saline and bronchodilator (terbutaline) aerosol droplets generated from four widely used jet nebulisers (Acorn, Upmist, Turret, and Inspiron Mini-neb) has been measured with a Malvern 2200 Laser Particle Sizer. The mass median diameter of aerosol droplets generated by each nebuliser was strongly influenced by the driving flow rate of compressed air. By increasing the flow rate from 4 to 81 min-' mass median diameters were halved (p < 0-01) and there was an increase in the mass of aerosol within the optimum respirable range (<5 ,m). To achieve this range the following individual flow rates were required: Turret 4 1 min-', Acorn and Upmist 6 1 min-t, and Inspiron Mini-neb 8 1 min-t. A significant inverse relation (p < 0.001) was found between mass median diameter and the geometric standard deviation, indicating that the aerosols were smaller but more heterodisperse at high flow rates. Changes in drug concentration had little effect on aerosol size. In 72% of the nebulisations followed to dryness there was no significant change in mass median diameter during the course of nebulisation and in the remainder it was less than 1-3 Am.

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Recently nebulised antibiotics (gentamicin and carbenicillin) have been used successfully to treat respiratory tract infection in patients with cystic fibrosis. No information exists, however, on the choice of nebuliser or the ideal mode of operation with antibiotic solutions, which are often viscous. The aerosol output, droplet size, and nebulisation time were assessed for four common brands of jet nebuliser (Bird, DeVilbiss, Inspiron, and Upmist) used to nebulise 2 ml (80 mg) and 4 ml (160 mg) of gentamicin solution (Garamycin, Kirby-Warrick) at four compressed gas flow rates (6, 8, 10, and 12 l.min-'). There were considerable variations between the nebulisers, DeVilbiss and Upmist being most efficient in the release of respirable (< 5 um diameter) droplets. Droplet size and nebulisation time were inversely proportional to gas flow rate. Aerosol output and nebulisation time were increased by raising the volume fill from 2 to 4 ml, although nebulisation time could still be restricted to 12 minutes or less with DeVilbiss and Upmist at 12 l.min-'. The output of drug in droplets of below 5 um diameter ranged from 7.2 (SE 0.4) to 71.4 (4.3) mg, according to the type of nebuliser, flow rate, and volume fill. These studies suggest that for optimal drug delivery 4 ml gentamicin solution should be nebulised either at a fixed flow rate of 10-12 l.min-' or with a high flow compressor. Previous unsatisfactory clinical results with antibiotic aerosols may have been due in part to incorrect choice of nebuliser or inappropriate operating conditions, or both.Treatment of chest disorders by inhaled drugs has several potential advantages over use of the oral or intravenous route in that a smaller dose of drug can often be used, there is a low incidence of systemic side effects, and the drug generally begins to act rapidly.' Antibiotics were first given by inhalation in 1946,2 but for many years this form of treatment was considered to have no particular advantage in the treatment of respiratory tract infection.3 Recent studies, however, have shown an improvement in pulmonary function4 and a reduction in the frequency of hospital admission5 in selected patients with cystic fibrosis and Pseudomonas aeruginosa infection when treated regularly with nebulised antibiotics. Aerosol antibiotics offer the prospect of domiciliary treatment over relatively long periods,6 and their use is associated with higher sputum and Address for reprint requests: Dr SP Newman, Department of Thoracic Medicine, Royal Free Hospital, London NW3 2QG. Surprisingly little information exists on the output characteristics of nebulisers, and there is no information at all on the nebulisation of antibiotic solutions, which are more viscous than saline or water.The present study was carried out to assess the output, droplet size, and nebulisation time of four common brands of jet nebuliser used with a solution of gentamicin at four different compressed gas flow rates, as a basis for guidelines for the most efficient delivery of nebulised antibiotics....

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