The effects of long-term noninvasive ventilation in hypercapnic COPD patients: a randomized controlled pilot study

Abstract

Introduction: Noninvasive ventilation (NIV) is a well-established treatment for acute-on- chronic respiratory failure in hypercapnic COPD patients. Less is known about the effects of a long-term treatment with NIV in hypercapnic COPD patients and about the factors that may predict response in terms of improved oxygenation and lowered CO(2) retention.

Methods: In this study, we randomized 15 patients to a routine pharmacological treatment (n = 5, age 66 [standard deviation ± 6] years, FEV(1) 30.5 [±5.1] %pred, PaO(2) 65 [±6] mmHg, PaCO(2) 52.4 [±6.0] mmHg) or to a routine treatment and NIV (using the Synchrony BiPAP device [Respironics, Inc, Murrsville, PA]) (n = 10, age 65 [±7] years, FEV(1) 29.5 [±9.0] %pred, PaO(2) 59 [±13] mmHg, PaCO(2) 55.4 [±7.7] mmHg) for 6 months. We looked at arterial blood gasses, lung function parameters and performed a low-dose computed tomography of the thorax, which was later used for segmentation (providing lobe and airway volumes, iVlobe and iVaw) and post-processing with computer methods (providing airway resistance, iRaw) giving overall a functional image of the separate airways and lobes.

Results: In both groups there was a nonsignificant change in FEV(1) (NIV group 29.5 [9.0] to 38.5 [14.6] %pred, control group 30.5 [5.1] to 36.8 [8.7] mmHg). PaCO(2) dropped significantly only in the NIV group (NIV: 55.4 [7.7] → 44.5 [4.70], P = 0.0076; control: 52.4 [6.0] → 47.6 [8.2], NS). Patients actively treated with NIV developed a more inhomogeneous redistribution of mass flow than control patients. Subsequent analysis indicated that in NIV-treated patients that improve their blood gases, mass flow was also redistributed towards areas with higher vessel density and less emphysema, indicating that flow was redistributed towards areas with better perfusion. There was a highly significant correlation between the % increase in mass flow towards lobes with a blood vessel density of >9% and the increase in PaO(2). Improved ventilation-perfusion match and recruitment of previously occluded small airways can explain the improvement in blood gases.

Conclusion: We can conclude that in hypercapnic COPD patients treated with long-term NIV over 6 months, a mass flow redistribution occurs, providing a better ventilation-perfusion match and hence better blood gases and lung function. Control patients improve homogeneously in iVaw and iRaw, without improvement in gas exchange since there is no improved ventilation/perfusion ratio or increased alveolar ventilation. These differences in response can be detected through functional imaging, which gives a more detailed report on regional lung volumes and resistances than classical lung function tests do. Possibly only patients with localized small airway disease are good candidates for long-term NIV treatment. To confirm this and to see if better arterial blood gases also lead to better health related quality of life and longer survival, we have to study a larger population.

Keywords: COPD; imaging; noninvasive ventilation.

Figure 1

Functional imaging derived from a high resolution computed tomography scan.

Figure 2

Mass flow (re)distribution (left) and change in airway resistance per lobe (right) in a patient treated with noninvasive ventilation for 6 months. Abbreviations: RUL, right upper lobe; RML, right middle lobe; RLL, right lower lobe; LUL, left upper lobe; LLL, left lower lobe.

Figure 3

Mass flow (re)distribution (left graph) and change in airway resistance per lobe (right graph) in a patient not treated with noninvasive ventilation for 6 months. Abbreviations: RUL, right upper lobe; RML, right middle lobe; RLL, right lower lobe; LUL, left upper lobe; LLL, left lower lobe.

Figure 4

Changes in PaO₂ (mmHg) in COPD patients treated with noninvasive ventilation for 6 months. Abbreviations: SE, standard error; SD, standard deviation.

Figure 5

Changes in PaO₂ (mmHg) in COPD patients treated without noninvasive ventilation (controls). Abbreviations: SE, standard error; SD, standard deviation; NS, not significant.

Figure 6

Internal mass flow redistribution was bigger in noninvasive ventilation (NIV)- treated patients than in controls. Notes: Imaging showed higher internal mass flow redistribution in NIV-treated patients: better V/Q matching due to airflow redistribution in NIV-treated patients.

Figure 7

Correlation between redistribution of mass flow towards well-perfused lung zones (>9% blood flow) and PaO₂ in COPD patients treated for 6 months with noninvasive ventilation. Notes: r = 0.95, P < 0.05 (Spearman Rank). Abbreviation: MF, mass flow.