Background: Spirometry has become an essential tool for general practices to diagnose and monitor chronic airways diseases, but very little is known about the performance of the spirometry equipment that is being used in general practice settings. The use of invalid spirometry equipment may have consequences on disease diagnosis and management of patients. Objectives: To establish the accuracy and precision of desktop spirometers that are routinely used in general practices. Methods: We evaluated a random sample of 50 spirometers from Dutch general practices by testing them on a certified waveform generator using 8 standard American Thoracic Society waveforms to determine accuracy and precision. Details about the brand and type of spirometers, year of purchase, frequency of use, cleaning and calibration were inquired with a study-specific questionnaire. Results: 39 devices (80%) were turbine spirometers, 8 (16%) were pneumotachographs, and 1 (2%) was a volume displacement spirometer. Mean age of the spirometers was 4.3 (SD 3.7) years. Average deviation from the waveform generator reference values (accuracy) was 25 ml (95% confidence interval 12–39 ml) for FEV1 and 27 ml (10–45 ml) for FVC, but some devices showed substantial deviations. FEV1 deviations were larger for pneumotachographs than for turbine spirometers (p < 0.0031), but FVC deviations did not differ between the two types of spirometers. In the subset of turbine spirometers, no association between age and device performance was observed. Conclusions: On average, desktop spirometers in general practices slightly overestimated FEV1 and FVC values, but some devices showed substantial deviations. General practices should pay more attention to the calibration of their spirometer.
We studied if pre-bronchodilator FEV1/FEV6 determinations with microspirometers by GPs improve the diagnostic process for COPD in a 6–8 month clustered randomised controlled trial in Dutch general practices (http://www.trialregister.nl: NTR4041). GPs allocated to microspirometry (MI) used COPD-6® microspirometers in patients ≥50 years old with a smoking history and respiratory complaints that could indicate undiagnosed COPD and ask to refer patients for full spirometry if MI was positive (FEV1/FEV6 <0.73). Introduction of the COPD-6® was postponed in the usual care (UC) group. GPs of both study arms were asked to list all patients that fulfilled study criteria and at the end of the study we screened the electronic medical record system for number of patients that fulfilled study criteria and visited their GP within the study period. Main end point was a documented diagnostic conclusion of COPD within 3 months after the patient’s visit. We used multilevel logistic regression with correction for relevant covariates. Next, we described the process of care. 21 practices (88 GPs) participated and 416 possible undiagnosed COPD patient visited these practices in the study period. 78 (of 192 visiting) subjects were listed by MI GPs and diagnostic conclusions were documented in 77%, compared to 61 listed (of 224 visiting) subjects and 44% with documented diagnostic conclusions by UC GPs (Odds Ratio: OR: 4.3, 95%CI: 1.6–11.5). Microspirometry improved the diagnostic process for possible underlying COPD in patients who consulted their GP with respiratory symptoms, but the majority of possible undiagnosed COPD patients remained unrecognised by GPs.
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