ATS Pulmonary Function Laboratory Manual

ATS Pulmonary Function Laboratory Management & Procedure Manual | 3rd Edition

3. The ATS/ERS 2005 recommendations (7) suggest the following increases represent significant bronchodila- tor responses in adult patients: FVC: at least 12% and 200 ml FEV 1 : at least 12% and 200 ml In children the 12% increase is applicable, but without the volume criterion. 4. Other flow measurements (e.g., forced expiratory flow after 50% of the FVC has been expired [FEF 50% ]) may be reported pre- and post-bronchodilator. Since these flows often depend on lung volume or on expiratory time, they should be corrected to reflect similar volumes (isovolume correction) (12). 5. If flow–volume curves pre- and post-bronchodilator are reported, they should be superimposed at TLC. If static lung volumes are also measured pre- and post-bronchodilator, the curves should be plotted on a com- mon volume axis. 6. The drug, dose, and method of delivery should be noted on the final report (2). Optionally, pulse and res- piratory rates pre- and post-bronchodilator delivery can be reported. Procedure Notes and Limitations 1. Because individuals vary their responses to various bronchodilators, 20% to 30% of responsive patients will respond to one agent but not another (13, 14). 2. The percent change in function after bronchodilator is a function of the degree of baseline airways obstruc- tion (e.g., % predicted FEV 1 ) (7). 3. Increases in FEV 1 or FVC of less than 8% or 150 ml are generally within the variability of the measurements themselves, and/or may represent a normal reduction in vagally mediated bronchomotor tone (2, 15). The decision to treat patients with bronchodilators is a clinical, not a laboratory decision. Failure to demonstrate a significant response to a single drug on one occasion does not preclude a clinical response to bronchodila- tor or antiinflammatory therapy (7). 5. Although PEF may be used to evaluate response to inhaled bronchodilators, its inherent variability makes it difficult to interpret. 6. The results from patients who did not perform acceptable or repeatable test maneuvers (either pre- or post-bronchodilator) should be interpreted with caution. However, bronchodilator response may need to be evaluated clinically in lieu of acceptable spirometry or plethysmography. For example, a patient who coughs uncontrollably or has spirometry-induced worsening may not be able to perform acceptable or reproducible spirometry until after administration of a bronchodilator. Post-bronchodilator spirometry that is performed acceptably may indicate significant improvement in this case, even though a percent change cannot be calculated. 7. Although the FEV 1 /FVC ratio should be reported pre- and post-bronchodilator, calculating the percent change in this parameter has less use than that of either of its components. 8. For midflow rates (FEF 50% or FEF 25-75% ), the increases representing a significant response are considerably greater than those for FVC and FEV 1 . However, Quanjer and colleagues reported that neither FEF 25-75% nor FEF 75% contribute usefully to clinical decision-making over and above information from FEV 1 , FVC, and FEV 1 /FVC ratio (16). 9. The FEF 25-75% is a highly variable parameter and is dependent on the FVC. If the FVC changes, post- bronchodilator, the FEF 25-75% is not comparable with that measured pre-bronchodilator (7).

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