Six methods to determine expiratory time constants in mechanically ventilated patients: a prospective observational physiology study
Abstract Background Expiratory time constant (τ) objectively assesses the speed of exhalation and can guide adjustments of the respiratory rate and the I:E ratio with the goal of achieving complete exhalation. Multiple methods of obtaining τ are available, but they have not been compared. The purpos...
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| Format: | Article |
| Language: | English |
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SpringerOpen
2024-03-01
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| Series: | Intensive Care Medicine Experimental |
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| Online Access: | https://doi.org/10.1186/s40635-024-00612-z |
| _version_ | 1797267003096956928 |
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| author | Filip Depta Caitlyn M. Chiofolo Nicolas W. Chbat Neil R. Euliano Michael A. Gentile Dušan Rybár Viliam Donič Marko Zdravkovic |
| author_facet | Filip Depta Caitlyn M. Chiofolo Nicolas W. Chbat Neil R. Euliano Michael A. Gentile Dušan Rybár Viliam Donič Marko Zdravkovic |
| author_sort | Filip Depta |
| collection | DOAJ |
| description | Abstract Background Expiratory time constant (τ) objectively assesses the speed of exhalation and can guide adjustments of the respiratory rate and the I:E ratio with the goal of achieving complete exhalation. Multiple methods of obtaining τ are available, but they have not been compared. The purpose of this study was to compare six different methods to obtain τ and to test if the exponentially decaying flow corresponds to the measured time constants. Methods In this prospective study, pressure, flow, and volume waveforms of 30 postoperative patients undergoing volume (VCV) and pressure-controlled ventilation (PCV) were obtained using a data acquisition device and analyzed. τ was measured as the first 63% of the exhaled tidal volume (VT) and compared to the calculated τ as the product of expiratory resistance (RE) and respiratory system compliance (CRS), or τ derived from passive flow/volume waveforms using previously published equations as proposed by Aerts, Brunner, Guttmann, and Lourens. We tested if the duration of exponentially decaying flow during exhalation corresponded to the duration of the predicted second and third τ, based on multiples of the first measured τ. Results Mean (95% CI) measured τ was 0.59 (0.57–0.62) s and 0.60 (0.58–0.63) s for PCV and VCV (p = 0.45), respectively. Aerts method showed the shortest values of all methods for both modes: 0.57 (0.54–0.59) s for PCV and 0.58 (0.55–0.61) s for VCV. Calculated (CRS * RE) and Brunner’s τ were identical with mean τ of 0.64 (0.61–0.67) s for PCV and 0.66 (0.63–069) s for VCV. Mean Guttmann’s τ was 0.64 (0.61–0.68) in PCV and 0.65 (0.62–0.69) in VCV. Comparison of each τ method between PCV and VCV was not significant. Predicted time to exhale 95% of the VT (i.e., 3*τ) was 1.77 (1.70–1.84) s for PCV and 1.80 (1.73–1.88) s for VCV, which was significantly longer than measured values: 1.27 (1.22–1.32) for PCV and 1.30 (1.25–1.35) s for VCV (p < 0.0001). The first, the second and the third measured τ were progressively shorter: 0.6, 0.4 and 0.3 s, in both ventilation modes (p < 0.0001). Conclusion All six methods to determine τ show similar values and are feasible in postoperative mechanically ventilated patients in both PCV and VCV modes. |
| first_indexed | 2024-04-25T01:09:40Z |
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| language | English |
| last_indexed | 2024-04-25T01:09:40Z |
| publishDate | 2024-03-01 |
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| spelling | doaj.art-b87d01108f8148e197040a0bf46f5eac2024-03-10T12:04:12ZengSpringerOpenIntensive Care Medicine Experimental2197-425X2024-03-0112111110.1186/s40635-024-00612-zSix methods to determine expiratory time constants in mechanically ventilated patients: a prospective observational physiology studyFilip Depta0Caitlyn M. Chiofolo1Nicolas W. Chbat2Neil R. Euliano3Michael A. Gentile4Dušan Rybár5Viliam Donič6Marko Zdravkovic7Department of Critical Care, East Slovak Institute for Cardiovascular DiseasesQuadrus Medical Technologies, IncQuadrus Medical Technologies, IncConvergent EngineeringDepartment of Anesthesia, Duke University Medical CenterDepartment of Critical Care, East Slovak Institute for Cardiovascular DiseasesDepartment of Physiology, Pavol Jozef Šafarik UniversityFaculty of Medicine, University of LjubljanaAbstract Background Expiratory time constant (τ) objectively assesses the speed of exhalation and can guide adjustments of the respiratory rate and the I:E ratio with the goal of achieving complete exhalation. Multiple methods of obtaining τ are available, but they have not been compared. The purpose of this study was to compare six different methods to obtain τ and to test if the exponentially decaying flow corresponds to the measured time constants. Methods In this prospective study, pressure, flow, and volume waveforms of 30 postoperative patients undergoing volume (VCV) and pressure-controlled ventilation (PCV) were obtained using a data acquisition device and analyzed. τ was measured as the first 63% of the exhaled tidal volume (VT) and compared to the calculated τ as the product of expiratory resistance (RE) and respiratory system compliance (CRS), or τ derived from passive flow/volume waveforms using previously published equations as proposed by Aerts, Brunner, Guttmann, and Lourens. We tested if the duration of exponentially decaying flow during exhalation corresponded to the duration of the predicted second and third τ, based on multiples of the first measured τ. Results Mean (95% CI) measured τ was 0.59 (0.57–0.62) s and 0.60 (0.58–0.63) s for PCV and VCV (p = 0.45), respectively. Aerts method showed the shortest values of all methods for both modes: 0.57 (0.54–0.59) s for PCV and 0.58 (0.55–0.61) s for VCV. Calculated (CRS * RE) and Brunner’s τ were identical with mean τ of 0.64 (0.61–0.67) s for PCV and 0.66 (0.63–069) s for VCV. Mean Guttmann’s τ was 0.64 (0.61–0.68) in PCV and 0.65 (0.62–0.69) in VCV. Comparison of each τ method between PCV and VCV was not significant. Predicted time to exhale 95% of the VT (i.e., 3*τ) was 1.77 (1.70–1.84) s for PCV and 1.80 (1.73–1.88) s for VCV, which was significantly longer than measured values: 1.27 (1.22–1.32) for PCV and 1.30 (1.25–1.35) s for VCV (p < 0.0001). The first, the second and the third measured τ were progressively shorter: 0.6, 0.4 and 0.3 s, in both ventilation modes (p < 0.0001). Conclusion All six methods to determine τ show similar values and are feasible in postoperative mechanically ventilated patients in both PCV and VCV modes.https://doi.org/10.1186/s40635-024-00612-zExpiratory time constantMechanical ventilationExhalationVolume-controlled ventilationPressure-controlled ventilation |
| spellingShingle | Filip Depta Caitlyn M. Chiofolo Nicolas W. Chbat Neil R. Euliano Michael A. Gentile Dušan Rybár Viliam Donič Marko Zdravkovic Six methods to determine expiratory time constants in mechanically ventilated patients: a prospective observational physiology study Intensive Care Medicine Experimental Expiratory time constant Mechanical ventilation Exhalation Volume-controlled ventilation Pressure-controlled ventilation |
| title | Six methods to determine expiratory time constants in mechanically ventilated patients: a prospective observational physiology study |
| title_full | Six methods to determine expiratory time constants in mechanically ventilated patients: a prospective observational physiology study |
| title_fullStr | Six methods to determine expiratory time constants in mechanically ventilated patients: a prospective observational physiology study |
| title_full_unstemmed | Six methods to determine expiratory time constants in mechanically ventilated patients: a prospective observational physiology study |
| title_short | Six methods to determine expiratory time constants in mechanically ventilated patients: a prospective observational physiology study |
| title_sort | six methods to determine expiratory time constants in mechanically ventilated patients a prospective observational physiology study |
| topic | Expiratory time constant Mechanical ventilation Exhalation Volume-controlled ventilation Pressure-controlled ventilation |
| url | https://doi.org/10.1186/s40635-024-00612-z |
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