Chest
Clinical Investigations: AntibioticsEffect of Size and Disease on Estimated Deposition of Drugs Administered Using Jet Nebulization in Children With Cystic Fibrosis
Section snippets
Theory
When the Bain anesthetic circuit was first introduced,16 there was concern that rebreathing expired gas would lead to hypercapnia. To investigate this, in 1983, Meakin and Coates17 developed a model that allowed partitioning of each inspiration into the volume of rebreathed gas, and the volume of fresh anesthetic gas. They justified their model by using the respiratory pattern, measured by a pneumotachograph placed at the distal end of the circuit, to predict the concentration of CO2 that would
Materials and Methods
The subjects had a diagnosis of CF18 and were being followed up in the CF clinic of the Montreal Children's Hospital. They were selected for their willingness and the ability to undergo pulmonary function testing. The Ethics Review Board of the institution had approved the study, and written informed consent was obtained from either the parent or guardian, or the patient, depending upon the age of the patient. Spirometry was performed according to American Thoracic Society guidelines.19 Lung
Results
Forty-three patients from 6 to 18 years of age participated in the study. They ranged in height from 108 to 173 cm, and their FEV1 values ranged from 26 to 124% predicted. Figure 3 shows the Bland and Altman25 plot of limits of agreement for the measured signal from the MS, and the calculated concentration for Ar. The bias ± 2 SDs indicates that the mathematical model successfully defined the pattern of ventilation and the dilution of the aerosol with ambient air. Based on the validity of the
Discussion
In this study, we have developed a model that allows the estimation of the inhaled mass in children with CF, over a wide range of size and disease severity. The inhaled mass when coupled with RF gives an estimate of pulmonary deposition of inhaled tobramycin. There is a striking relationship between estimated deposition normalized for body weight and the height of the child. This suggests that standard doses of medications administered by unvented jet nebulization may result in overdosing small
Appendix
Volume areas 1 to 4 (Fig 2), when summed together, represent the total nebulizer output (aerosol). The equations for each subvolume are as follows:
Also, note that at times t1 and t2, n = p(t1) and p(t2). Now,
% Aerosol
Defining pnt(t) as positive for inspiratory flow when pnt(t) > n, then:
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Supported by the Canadian Cystic Fibrosis Foundation.