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Otto-von-Guericke-Universität Magdeburg, Pulmonary and Intensive Care Medicine, Leipziger Strasse 44, D-39120, Mageburg, Germany
To the Editor:
Chronic obstructive pulmonary disease (COPD) with severe emphysema is a continuously progressing disease, resulting in respiratory failure. Pharmacological treatment may be optimised in the last years, but only the introduction of long-term oxygen treatment has revealed an improvement in survival for patients with advanced COPD 1.
Noninvasive positive pressure ventilation (NPPV) is a new approach to directly correct ventilatory insufficiency. The beneficial effects of NPPV during acute exacerbation of COPD are well documented 2, and NPPV is frequently applied in these patients today 3. However, domiciliary long-term use of NPPV by patients with severe COPD remains controversial.
In 1996, the Italian Rehabilitation and Chronic Care Study Group started a prospective, randomised, controlled, multicentre trial to evaluate NPPV in severe chronic stable COPD. The main outcome parameters were arterial blood gases, hospital and intensive care unit admissions and length of stay, health related quality of life, and exercise tolerance. The results of this study had been recently presented in the European Respiratory Journal 4. The conclusions drawn are not in favour of long-term use of NPPV in severe COPD patients. Apart from a quality of life assessment (Maugeri Foundation Respiratory Questionnaire (MRF-28)), none of the other outcome parameters could be significantly improved. The reason for this should be sought in the "ventilator setting" instructions of the protocol: ventilator settings were titrated individually for each patient with the target of maximally tolerated inspiratory pressures and expiratory pressures in the range of 2–5 cm·H2O. However, a reduction of baseline carbon dioxide arterial tension by 
5% during 1 h of daytime NPPV had been considered an effective treatment (E. Clini, Fondazione Villa Pineata ONLUS, Italy, personal communication). This resulted in a mean inspiratory pressure of 14±3 cm·H2O and a mean expiratory pressure of 2±1 cm·H2O.
The findings of the study by Clini et al. 4 are in accordance with the survival and hospital admission rates reported by Casanova et al. 5, who applied NPPV in a similar cohort of COPD patients with a mean inspiratory pressure of 12 cm·H2O and a mean expiratory pressure of 4 cm·H2O. However, in 1995 Meecham-Jones et al. 6 demonstrated significant improvements of blood gases, sleep quality and quality of life in hypercapnic COPD patients after 3 months of NPPV with a mean inspiratory pressure of 20 cm H2O.
It is reasonable to speculate that the applied pressures in the study by Meecham-Jones et al. 6 resulted in better gas exchange and unloading of the ventilatory muscles. NPPV might otherwise be "underdosed" in patients with severe COPD and the therapeutic goal of correcting the underlying pathophysiology is missed. It can be troublesome to establish NPPV in patients with severe COPD and with growing ventilatory pressures it becomes more and more difficult to keep the patient compliant. The balance between therapeutic requirements and patients’ comfort is a challenge for both patient and staff.
Further studies confirming and extending the findings of Meecham-Jones et al. 6 findings to define the role of noninvasive positive pressure ventilation as a treatment option for patients with severe chronic obstructive pulmonary disease are needed.
References
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