The appropriate setting of noninvasive pressure support ventilation in stable COPD patients

Study objective: To evaluate the short-term physiologic effects of two sett ings of nasal pressure-support ventilation (NPSV) in stable COPD patients w ith chronic hypercapnia. Design: Randomized controlled physiologic study. Setting: Lung function units and outpatient clinic of two affiliated pulmon ary 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 wer e randomly applied for 30 min each: (1) usual setting (U), the setting of N PSV actually used by the individual patient at home; and (2) physiologic se tting (PNY), the level of inspiratory pressure support (IPS) and external p ositive end-expiratory pressure (PEEPe) tailored to patient according to in vasive 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, 1 5 +/- 3 cm H2O and PEEPe, 3.1 +/- 1.6 cm H2O. NPSV was able to significantl y (p < 0.01) improve arterial blood gases independent of the setting applie d. When compared with spontaneous breathing, both settings induced a signif icant increase in minute ventilation (p < 0.01). Both settings were able to reduce the diaphragmatic pressure-time product, but the reduction was sign ificantly 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 PNY show ed ineffective efforts (IE); the prevalence of IE (20 +/- 39% vs 6 +/- 11% of their respiratory rate with U and PHY, respectively) was statistically d ifferent (p < 0.05). Conclusion: In COPD patients with chronic hypercapnia, NPSV is effective in improving arterial blood gases. and in unloading inspiratory muscles indep endent 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 effo rt and mechanics. However, setting of inspiratory assistance and PEEPe by t he invasive evaluation of lung mechanics and respiratory muscle function ma y result in reduction in ineffective inspiratory efforts. These short-term results must he confirmed in the long-term clinical setting.