ATS Pulmonary Function Laboratory Manual

cHAPTER 7

In most instances, spirometry or plethysmography is performed, followed by administration of a bronchodilator, then the test repeated after an appropriate interval. The delay from pre- to post-test should be determined by the time it takes for the onset of action to peak effect for the drug used. For most short-acting beta-agonists this is a relatively short interval (i.e., ≥ 10 min) (3). Other drugs, such as short-acting anticholinergics may require a longer interval before retesting (e.g., ≥ 30 min). The method of administration of bronchodilators can have a pronounced effect on the results of pre- and post- tests (4, 5). Beta-agonists and anticholinergics are often administered via an inhaler or via a small-volume nebulizer (SVN). Other methods may be used for specific bronchodilator preparations. In order to maximize lung deposition of the bronchodilator, valve-holding chambers (spacers) should be used in conjunction with metered dose inhalers (MDIs) (6). There is no clear consensus about what constitutes reversibility in patients with airflow limitation. The most common approaches of expressing bronchodilator response are percent of the initial PF test value, percent of the predicted value, and absolute change (7). The most commonly used variables for evaluation of response to bron- chodilators are forced expiratory volume in one second (FEV 1 ), forced vital capacity (FVC), peak expiratory flow (PEF), and sGaw. Other variables (e.g., thoracic gas volume [TGV], isovolume maximal expiratory flows) may iden- tify response to bronchodilators when more conventional measures do not. PF tests that measure parameters that are not flow related (e.g., carbon monoxide diffusing capacity [Dl CO ], total lung capacity [TLC]) are also sometimes evaluated pre- and post-bronchodilator administration. However, there are few guidelines for these other variables and using them may increase the number of false positives. Indications and contraindications for bronchodilator response testing are shown in Table 7.2. Equipment and Supplies 1. PF testing instrumentation (e.g., spirometer, plethysmograph). 2. Inhaler or nebulizer and liquid bronchodilator as used by the laboratory. Specify the dosage. 3. A valve-holding chamber or “spacer” for use in conjunction with an MDI should be available. The volume of the spacer should be appropriate for the type of patients tested (i.e., children or adults) (2).

Table 7.2

Indications and Contraindications for Bronchodilator-Response Testing

Indications

Reversibility of airway obstruction as demonstrated by a reduced FEV 1 or other indicators of flow limitation Evaluation of specific drug regimens in patients with known hyperreactive airways Reversal of bronchospasm induced by bronchial challenge tests Disability determinations when the FEV 1 is less than 70% of predicted Preoperative evaluation when airway obstruction is present Known or suspected adverse reactions to a specific bronchodilator Unstable cardiovascular status (i.e., serious arrhythmias, significant tachycardia, and elevated blood pressure) that might be aggravated by beta adrenergic stimulation /FVC ratio

Relative Contraindications

67