Results

The median (95% confidence intervals) ages of children in the first, second, and third studies were 52 (47–56), 51 (44–54), and 61 (54–72) months respectively. In the third study, children in the younger (3–5 year) group were 46 (42–51) months while those in the older group were 79 (75–85) months.

Table 1 summarises the results of lung deposition of aerosol. The median (95% confidence intervals) aerosol deposition in the lungs from the Babyhaler and Aerochamber with facemasks was 25% (15.2–28.6) and 21% (18.1–27.3) respectively, which were not significantly different. Median aerosol deposition from the Babyhaler with mask compared to the Babyhaler with mouthpiece was the same (26% in both). However, aerosol lung deposition was significantly higher from a 500 ml bottle compared to the Babyhaler with mouthpiece for both young (25% (19.7–31.5) compared to 12.5% (6.5–19.5), p = 0.005) and older children (42% (36.0–44.0) compared to 22.5% (15.9–27.7), p = 0.003).

The age of the child affected the amount of aerosol deposited in the lungs, with decreased deposition occurring in younger children. At approximately 50 months of age, there was a notable reduction in the amount of pulmonary deposition obtained when the bottle was used as a spacer (fig 1). Of the children younger than 50 months of age, one had pulmonary deposition of more than 30%, while only a single child older than 50 months had deposition less than 30%. This pattern of deposition was similar for the Babyhaler but at a lower level. For the Babyhaler, only one child younger than 55 months had deposition of more than 19%, while seven of 10 children older than 55 months had deposition of more than 19%. Children in the 3–5 year age group of the third study were younger than those in the second study; this probably accounts for the lower aerosol deposition obtained from a Babyhaler in the former study.

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Figure 1

Pulmonary aerosol deposition from a bottle used as a spacer by age.

Discussion

This study showed that a modified 500 ml plastic bottle produced greater pulmonary aerosol lung deposition than a small volume conventional spacer, the Babyhaler. This effect was seen in children of various ages. Two widely available small volume spacers, the Babyhaler and Aerochamber produced equivalent aerosol lung deposition in young children. Furthermore, aerosol deposition did not differ whether a mask or mouthpiece was used.

Many properties of a spacer may affect pulmonary deposition of aerosol, including the volume and shape of the device, the electrostatic charge of the side walls, volume of dead space, and presence or type of valves.8-10 The efficiency of a 500 ml bottle may be partly a result of its physical characteristics. A 500 ml bottle was selected in preference to a larger volume bottle as it more closely approximates the optimum chamber dimensions for a spacer for children (experimentally found to be a cylinder approximately 11 cm in length by 3.5 cm in diameter).8 Furthermore, a 500 ml bottle has been previously reported to be an effective spacer, producing equivalent aerosol deposition and bronchodilation to that obtained from a conventional spacer in older children.5 11 Our results suggest that the absence of a one way valve (as occurs with a bottle) does not adversely affect aerosol deposition but may in fact increase the amount of aerosol delivered. Valveless spacers have been reported to enhance the delivery of aerosol to the lungs in infants with chronic lung disease.12 Similarly, absence of a valve may prove beneficial for children as the need to overcome the resistance of the valve on inspiration is obviated.

Although the Aerochamber is less than half the volume of the Babyhaler, equivalent aerosol deposition was obtained from both devices. The choice of spacer size must balance the need for a small volume with the loss of aerosol because of impaction on the side walls which increases as the volume diminishes.13 Previous studies have reported that larger doses of aerosol are obtainable from the Babyhaler than the Aerochamber.13 14 However, these studies measured the drug collected on filter paper interposed after the inspiratory valve of the spacer; thus they reflect the dose of aerosol delivered at the child's mouth and not the amount deposited in the lungs. The reduction in lung aerosol deposition because of the smaller volume of the Aerochamber may be countered by the large dead space in the Babyhaler, thus explaining the equivalence of these spacers.

Characteristics of the child such as their tidal volume, breathing pattern, and technique of spacer usage may further affect drug deposition.15 16 As evidence of this, reduced deposition of aerosol occurred at approximately 50 months of age with all spacers. Reasons for this may be related to the ability of the child to cooperate as well as age dependent differences in pulmonary mechanics. Lower tidal volumes and inspiratory flow rates generated with younger age, decrease pulmonary aerosol delivery resulting in substantially less lung deposition in young children compared to older subjects.17

An MDI with mouthpiece rather than facemask has been recommended for children 3–5 years old. The current British Thoracic Guidelines for the management of childhood asthma advise use of a spacer with mask for children under 2 years.18 Our study suggests that the mouthpiece and mask produce equivalent aerosol deposition. Although aerosol leakage from the perimeter of the mask where it fits onto the face may result in lower lung deposition, this did not appear to be a problem. However, we were careful to use a well fitting mask that was firmly applied to the face. Choice of the delivery method should be based on the availability and cost of the system as well as the ability and preference of the individual child. Whether a facemask or mouthpiece is selected, the correct technique for use of the delivery system should be carefully demonstrated to the care giver.

Exposure of children to radiation raises ethical concern. However, the total radiation dose for each child in this study was extremely small. The estimated dose of radiation that children were exposed to is far less than that obtained from a single abdominalx ray and may be similar to the amount of naturally occurring radiation that is acquired daily.

The method of aerosol delivery in our study differs from that of an MDI. We have previously developed and tested this delivery system in older children.5 The aerosol used was generated via a jet nebuliser that produces particles with a mass median aerodynamic diameter of 2–4 μm. Lung deposition of aerosol from an MDI might differ from that attained using our delivery system. However, the percentage deposition obtained is not important, but rather the relative deposition from different spacers. As the delivery system was kept constant and the particular spacer varied, a valid comparison of the efficacy of different spacers could be made.

In conclusion, a modified 500 ml plastic bottle produced superior aerosol deposition to that obtained from a conventional small volume valved spacer. The Aerochamber and Babyhaler were equivalent in the amount of pulmonary aerosol deposition produced. Use of a mouthpiece rather than a facemask did not increase the amount of aerosol deposited in the respiratory tract in children older than 3 years. The choice of spacer and use of mask or mouthpiece should be made based on consideration of factors such as patient preference, cost of the device, ability of the care giver or patient to use the spacer correctly, and type of MDI used. Use of a 500 ml modified bottle as a spacer for children requiring inhaled therapy for asthma should be encouraged.