To study how choice of reference value database impacts the way pulmonary function tests are interpreted in patients being evaluated for bariatric surgery.
All pulmonary function tests obtained during preoperative assessment for bariatric surgery were studied. Each test was compared to the reference values from three databases; Crapo, Knudson, and the National Health and Nutrition Examination Survey. The impact of choice of reference value on the interpretation of the tests was measured. We then calulated the difference in degree of impairment in each measurement predicted by the various databases.
We reviewed 71 pulmonary function tests (for 71 patients), 61 of whom were female. There was agreement between the databases in the interpretation of all components of the test in 9 of the studies (12.7%). When applying the different reference values, there would be a different interpretation for spirometry in 6 of the tests (8.5%), for lung volume measurements in 56 of the tests (78.9%), and for the diffusing capacity in 23 of the tests (32.4%).The degree of variability in impairment when compared to the reference values was calculated. The average difference when compared to the reference value for the forced expiratory volume in 1 second was 16.4%, for the forced vital capacity was 14.2%, for the residual volume was 15.8%, for the functional residual capacity was 39.5%, and for the diffusing capacity was 12.2%. The total lung capacity had a uniform interpretation.When stratified by age, sex, and body mass index, no specific predictor for a variable interpretation was identified.
The interpretation of a pulmonary function test in a morbidly obese patient varies considerably depending on which reference value database is used for the predicted values.
Consideration should be given to the development of a pulmonary function reference database specific to this subpopulation, rather than applying correction equations to the existing ones.
Jafar Abunasser, No Financial Disclosure Information; No Product/Research Disclosure Information