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Expiratory flow‐volume curves in mechanically ventilated patients with chronic obstructive pulmonary disease
Author(s) -
Aerts J. G. J. V.,
Van Den Berg B.,
Lourens M. S.,
Bogaard J. M.
Publication year - 1999
Publication title -
acta anaesthesiologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.738
H-Index - 107
eISSN - 1399-6576
pISSN - 0001-5172
DOI - 10.1034/j.1399-6576.1999.430313.x
Subject(s) - medicine , copd , lung volumes , cardiology , pulmonary disease , anesthesia , ventilation (architecture) , lung , mechanical engineering , engineering
Background: Forced expiratory flow‐volume curves are commonly used to assess the degree of airflow obstruction in patients with chronic obstructive pulmonary disease (COPD). In mechanically ventilated subjects, expiratory airways obstruction can only be estimated from relaxed expirations. The aim of this study was to quantify the degree of airways obstruction from relaxed expiratory flow‐volume curves in mechanically ventilated patients with COPD. Methods: As measure of airflow obstruction, the effective time constant during the last 50% of expired volume (τ) was calculated. For bedside monitoring, τ was recalculated as the slope of the flow during the last 50% of expired volume (SF50). In order to study reproducibility, the variables were calculated from consecutive breaths and at different levels of end‐expiratory lung volume (EEV). The SF50 and the τ were correlated with the forced expiratory volume in 1 s (FEV 1 ) measured prior to the start of ventilatory support. Results: Twenty‐seven patients were studied with a FEV 1 expressed as percentage predicted of 31±12% (mean±SD). The SF50 amounted to 19±10°. A positive linear correlation was established between SF50 and the FEV 1 , (%pred), (r=0.90, P <0.0001). The τ showed an exponential relationship with FEV 1 (%pred), (r 2 =0.78) From 5 consecutive breaths the mean variation coefficient of SF50 was 5±2%. Changes of ΔEEV from 0.05 to 1.00 L did not affect the SF50‐values. In 12 patients, mechanically ventilated for respiratory diseases other than COPD, mean τ and SF50 were significantly different from the COPD‐patients ( P <0.0001). Conclusions: This study indicates that relaxed expiratory flow‐volume curves can be used to assess airflow obstruction in mechanically ventilated patients with COPD. This information can be used to adapt ventilatory settings.