Appropriate Setting
The Appropriate Setting of Noninvasive Pressure Support Ventilation in
Stable COPD Patients
Design: Randomized controlled physiologic study.
Setting: Lung function units and outpatient clinic of two affiliated
pulmonary rehabilitation centers. Patients: Twenty-three patients receiving
domiciliary nocturnal NPSV for a mean (± SD) duration of 31 ± 20 months.
Methods: Evaluation of arterial blood gases, breathing pattern, respiratory
muscles, and dynamic intrinsic positive end-expiratory pressure (PEEPi,dyn)
during both unassisted and assisted ventilation. Two settings of NPSV were
randomly applied for 30 min each: (1) usual setting (U), the setting of NPSV
actually used by the individual patient at home; and (2) physiologic setting (PHY),
the level of inspiratory pressure support (IPS) and external positive
end-expiratory pressure (PEEPe) tailored to patient according to invasive
evaluation of respiratory muscular function and mechanics.
Results: All patients tolerated NPSV well throughout the procedure. Mean U
was IPS, 16 ± 3 cm H2O and PEEPe, 3.6 ± 1.4 cm H2O; mean PHY was IPS, 15 ± 3 cm
H2O and PEEPe, 3.1 ± 1.6 cm H2O. NPSV was able to significantly (p < 0.01)
improve arterial blood gases independent of the setting applied. When compared
with spontaneous breathing, both settings induced a significant increase in
minute ventilation (p < 0.01). Both settings were able to reduce the
diaphragmatic pressure-time product, but the reduction was significantly greater
with PHY (by 64%; p < 0.01) than with U (56%; p < 0.05). Eleven of 23 patients
(48%) with U and 7 of 23 patients (30%) with PHY showed ineffective efforts
(IE); the prevalence of IE (20 ± 39% vs 6 ± 11% of their respiratory rate with U
and PHY, respectively) was statistically different (p < 0.05).
Conclusion: In COPD patients with chronic hypercapnia, NPSV is effective in
improving arterial blood gases and in unloading inspiratory muscles independent
of whether it is set on the basis of patient comfort and improvement in arterial
blood gases or tailored to a patient’s respiratory muscle effort and mechanics.
However, setting of inspiratory assistance and PEEPe by the invasive evaluation
of lung mechanics and respiratory muscle function may result in reduction in
ineffective inspiratory efforts. These short-term results must be confirmed in
the long-term clinical setting.
Key Words: breathing pattern • hypercapnia • noninvasive mechanical
ventilation • respiratory failure • respiratory muscles
