Evaluating How Post-Bronchodilator Vital Capacities Affect the Diagnosis of Obstruction in Pulmonary Function Tests.

BACKGROUND: Although the ratio of FEV1 to the vital capacity (VC) is universally accepted as the cornerstone of pulmonary function test (PFT) interpretation, FVC remains in common use. We sought to determine what the differences in PFT interpretation were when the largest measured vital capacity (VCmax) was used instead of the FVC. METHODS: We included 12,238 consecutive PFTs obtained for routine clinical care. We interpreted all PFTs first using FVC in the interpretation algorithm and then again using the VCmax, obtained either before or after administration of inhaled bronchodilator. RESULTS: Six percent of PFTs had an interpretive change when VCmax was used instead of FVC. The most common changes were: new diagnosis of obstruction and exclusion of restriction (previously suggested by low FVC without total lung capacity measured by body plethysmography). A nonspecific pattern occurred in 3% of all PFT interpretations with FVC. One fifth of these 3% produced a new diagnosis of obstruction with VCmax. The largest factors predicting a change in PFT interpretation with VCmax were a positive bronchodilator response and the administration of a bronchodilator. Larger FVCs decreased the odds of PFT interpretation change. Surprisingly, the increased numbers of PFT tests did not increase odds of PFT interpretation change. CONCLUSIONS: Six percent of PFTs have a different interpretation when VCmax is used instead of FVC. Evaluating borderline or ambiguous PFTs using the VCmax may be informative in diagnosing obstruction and excluding restriction.

Comparison of NHANES III and ERS/GLI 12 for airway obstruction classification and severity.

The diagnosis and severity categorisation of obstructive lung disease is determined using reference values. The American Thoracic Society/European Respiratory Society in 2005 recommended the National Health and Nutrition Examination Survey (NHANES) III spirometry prediction equations for patients in USA aged 8-80 years. The Global Lung Initiative 2012 (GLI 12) provided spirometry prediction equations for patients aged 3-95 years. Comparison of the NHANES III and GLI 12 prediction equations for diagnosing and categorising airway obstruction in patients in USA has not been made.We aimed to quantify the differences between NHANES III and GLI 12 predicted values in Caucasians aged 18-95 years, using both mathematical simulation and clinical data. We compared predicted forced expiratory volume in 1 s (FEV1) and lower limit of normal (LLN) FEV1/forced vital capacity (FVC) % for NHANES III and GLI 12 prediction equations by applying both a simulation model and clinical spirometry data to quantify differences in the diagnosis and categorisation of airway obstruction.Mathematical simulation revealed significant similarities and differences between prediction equations for both LLN FEV1/FVC % and predicted FEV1 There are significant differences when using GLI 12 and NHANES III to diagnose airway obstruction and severity in Caucasian patients aged 18-95 years.Similarities and differences exist between NHANES III and GLI 12 for some age and height combinations. The differences in LLN FEV1/FVC % and predicted FEV1 are most prominent in older taller/shorter individuals. The magnitude of the differences can be large and may result in differences in clinical management.

Standardizing Predicted Body Weight Equations for Mechanical Ventilation Tidal Volume Settings.

BACKGROUND: Recent recommendations for lung protective mechanical ventilation include a tidal volume target of 6 mL/kg predicted body weight (PBW). Different PBW equations might introduce important differences in tidal volumes delivered to research subjects and patients. METHODS: PBW equations use height, age, and sex as input variables. We compared National Institutes of Health (NIH) ARDS Network (ARDSNet), actuarial table (ACTUARIAL), and Stewart (STEWART) PBW equations used in clinical trials, across physiologic ranges for age and height. We used three-dimensional and two-dimensional surface analysis to compare these PBW equations. We then used age and height from actual clinical trial subjects to quantify PBW equation differences. RESULTS: Significant potential differences existed between these PBW predictions. The ACTUARIAL and ARDSNet surfaces for women were the only surfaces that intersected and produced both positive and negative differences. Mathematical differences between PBW equations at limits of height and age exceeded 30% in women and 24% in men for ACTUARIAL vs ARDSNet and about 25% for women and 15% for men for STEWART vs ARDSNet. The largest mathematical differences were present in older, shorter subjects, especially women. Actual differences for clinical trial subjects were as high as 15% for men and 24% for women. CONCLUSIONS: Significant differences between PBW equations for both men and women could be important sources of interstudy variation. Studies should adopt a standard PBW equation. We recommend using the NIH National Heart, Lung, and Blood Institute ARDS Network PBW equation because it is associated with the clinical trial that identified 6 mL/kg PBW as an appropriate target.

Spirometric reference values for Malagasy adults aged 18-73 years.

The American Thoracic Society (ATS) and European Respiratory Society (ERS) recommend that spirometry prediction equations be derived from samples of similar race/ethnicity. Malagasy prediction equations do not exist. The objectives of this study were to establish prediction equations for healthy Malagasy adults, and then compare Malagasy measurements with published prediction equations. We enrolled 2491 healthy Malagasy subjects aged 18-73 years (1428 males) from June 2006 to April 2008. The subjects attempted to meet the ATS/ERS 2005 guidelines when performing forced expiratory spirograms. We compared Malagasy measurements of forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC) and FEV1/FVC with predictions from the European Community for Steel and Coal (ECSC), the third National Health and Nutrition Examination Survey (NHANES III) and the ERS Global Lung Function Initiative (GLI) 2012 study. A linear model for the entire population, using age and height as independent variables, best predicted all spirometry parameters for sea level and highland subjects. FEV1, FVC and FEV1/FVC were most accurately predicted by NHANES III African-American male and female, and by GLI 2012 black male and black and South East Asian female equations. ECSC-predicted FEV1, FVC and FEV1/FVC were poorly matched to Malagasy measurements. We provide the first spirometry reference equations for a healthy adult Malagasy population, and the first comparison of Malagasy population measurements with ECSC, NHANES III and GLI 2012 prediction equations.

Comparison between cerebral state index and bispectral index as measures of electroencephalographic effects of sevoflurane using combined sigmoidal E(max) model.

AIM: The cerebral state index (CSI) was recently introduced as an electroencephalographic monitor for measuring the depth of anesthesia. We compared the performance of CSI to the bispectral index (BIS) as electroencephalographic measures of sevoflurane effect using two combined sigmoidal E(max) models. METHODS: Twenty adult patients scheduled for laparotomy were studied. After induction of general anesthesia, sevoflurane concentrations were progressively increased and then decreased over 70 min. An analysis of the BIS and CSI with the sevoflurane effect-site concentration was conducted using two combined sigmoidal E(max) models. RESULTS: The BIS and CSI decreased over the initial concentration range of sevoflurane and then reached a plateau in most patients. A further increase in sevoflurane concentration produced a secondary plateau in the pharmacodynamic response. The CSI was more strongly correlated with effect-site sevoflurane concentration (R(2)=0.95±0.04) than the BIS was (R(2)=0.87±0.07) (P<0.05). The individual E(max) and C(eff50) (effect-site concentration associated with 50% decrease from baseline to plateau) values for the upper and lower plateaus were significantly greater for BIS (12.7±7.3, 1.6±0.4, and 4.2±0.5, respectively) than for CSI (3.4±2.2, 1.2±0.4, and 3.8±0.5, respectively) (P<0.05). The remaining pharmacodynamic parameters for the BIS and CSI were similar. CONCLUSION: The overall performance of the BIS and CSI during sevoflurane anesthesia was similar despite major differences in their algorithms. However, the CSI was more consistent and more sensitive to changes in sevoflurane concentration, whereas the measured BIS seemed to respond faster. The newly developed combined E(max) model adequately described the clinical data, including the pharmacodynamic plateau.