I read with interest the study(1), comparing the efficacy of jet nebulizers and metered dose inhalers (MDIs) with spacers in the management of acute asthma in children. The authors have correctly pointed out several disadvantages of nebulizer use in pediatric population, to which I would like to add a few, As airway resistance is inversely related to the fourth power of airway radius, bronchospasm considerably increases airway resistance in an already narrow pediatric airway, and encourages central deposition of nebulized drugs. Aerosol particle size need to be reduced further (by altering nebulizer design) and nebulization time lengthened to overcome this problem, neither of which is easy. Sec- ondly, viscous steroid suspensions are not easily nebulized. Thirdly, nasal breathing has been shown to reduce lung deposition of nebulized drugs by almost 50%(2), and most children breathe nasally (unless an oral mouthpiece is used in older children). This does not mean that MDIs with spacers are uniformly superior in such a setting. Optimum spacer use involves slow deep inhalation with breath holding, which may be difficult for sick children. In fact, some patients may not even generate adequate flows to trigger the spacer valve(3). Thus, aerosol therapy in children should be individualized.

The authors also state that about 12% of the nebulized aerosol reaches the lung. Such figures are true only in adults. Studies in children have shown that less than 3% of the nebulized drug is delivered to the lung, and this fraction may be still less in younger children(4,5). Nevertheless, this poor deposition is compensated for by the smaller size of their body (and lungs), so that the final dose per unit body weight (or per unit lung volume) reaching the lungs may be very similar to that of an adult.
 

Ashutosh Nath Aggarwal,
Senior Resident,
Department of Pulmonary Medicine,
Postgraduate Institute of Medical
Education and Research,
Chandigarh 160012, India.
 

1. Batra V, Sethi GR, Sachdev HPS. Comparative efficacy of jet nebulizer and metered dose inhaler with spacer device in the treatment of acute asthma. Indian Pediatr 1997; 34: 497-503.

2. Everard ML, Hardy JG, Milner AD. Comparison of nebulized aerosol deposition in the lungs of healthy adults following oral and nasal inhalation. Thorax 1993; 48: 1045-1046.

3. Freelander M, vanAsperen PP. Nebuhaler versus nebulizer in children with acute asthma. BMJ 1984; 288: 1873-1874.

4. Salman B, Wilson NM, Silverman M. How much aerosol reaches the lungs of wheezy infants and toddlers. Arch Dis Child 1990; 65: 401-403.

5. Chua HL, Collis GG, Newbury AM, Chan K, Bower GD, Sly PD, et al. The influence of age on aerosol deposition in children with cystic fibrosis. Eur Respir J 1994; 7: 2185-2191.