Background -The factors leading to chronic hypercapnia and rapid shallow breathing in patients with severe chronic obstructive pulmonary disease (COPD) are not completely understood. In this study the interrelations between chronic carbon dioxide retention, breathing pattern, dyspnoea, and the pressure required for breathing relative to inspiratory muscle strength in stable COPD patients with severe airflow obstruction were studied.Methods -Thirty patients with COPD in a clinically stable condition with forced expiratory volume in one second (FEV1) of <1 litre were studied. In each patient the following parameters were assessed: (1) dyspnoea scale rating, (2)

Results -There were 45 treatment failures (30%) and 36 deaths (24%). Nine patients (6%) required intubation because of lack of airway control. The median total duration of ventilation was 27 hours per patient (range 2-274). The 105 successfully treated cases recovered consciousness after a median of four hours (range 1-90) of continuous ventilatory treatment and were discharged after 12.1 (9.0) days. Conclusions -These results show that, in patients with acute on chronic respiratory failure and hypoxic hypercapnic coma, the iron lung resulted in a high rate ofsuccess. As this study has the typical limitations of all retrospective and uncontrolled studies, the results need to be formally confirmed by controlled prospective studies. Confirmation of these results could widen the range of application of non-invasive ventilatory techniques.

aaPatients with chronic pulmonary disease frequently need mechanical ventilatory support for acute exacerbation of the disease. In these patients, however, endotracheal intubation and mechanical ventilation lead to several complications including tracheal injury, barotrauma, nosocomial pneumonia, and weaning difficulty [1]. Complications and difficulty in weaning are the major factors in increasing the duration of hospitalization and for high costs, principally linked to the length of stay in very expensive facilities such as intensive care units (ICU).It has been shown that, in chronic obstructive pulmonary disease (COPD) patients with acute respiratory failure (ARF), noninvasive positive pressure ventilation (NIPPV) reduces the need for endotracheal intubation [2][3][4], the length of hospital stay [2,3] and the inhospital mortality rate [2][3][4][5], compared with standard therapy. The implementation of NIPPV at a much earlier stage in the course of respiratory failure than that at which intubation is normally considered could prevent the development of a severe acidosis, which has been found to be a poor prognostic feature for recovery [6]. The selection of patients is a crucial factor in the success of NIPPV [7] and this means that patients more severely ill than those included in previous studies [2-5] could not benefit from noninvasive mechanical ventilation; in these cases, conventional mechanical ventilation after intubation must be provided promptly. A recent study, however, has reported that COPD patients with severe respiratory acidosis and hypercapnic coma were successfully treated with a noninvasive ventilatory technique using negative pressure ventilation [8]. Direct comparisons between noninvasive and conventional mechanical ventilation in the treatment of COPD patients with ARF are scarce. In the only retrospective study, published recently by VITACCA et al. [9], the control These results suggest that negative pressure ventilation is as efficacious as conventional mechanical ventilation for the treatment of acute respiratory failure in patients with chronic obstructive pulmonary disease and that it is associated with a shorter duration of ventilation and a similar length of hospital stay compared with conventional mechanical ventilation. Eur Respir J 1998; 12: 519-525.

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Negative pressure ventilation in the treatment of acute respiratory failure: an old noninvasive technique reconsidered. A. Corrado, M. Gorini, G. Villella, E. De Paola. ©ERS Journals Ltd 1996. ABSTRACT: Noninvasive mechanical ventilatory techniques include the use of negative and positive pressure ventilators. Negative pressure ventilators, such as the "iron lung", support ventilation by exposing the surface of the chest wall to subatmospheric pressure during inspiration; whereas, expiration occurs when the pressure around the chest wall increases and becomes atmospheric or greater than atmospheric.In this review, after a description of the more advanced models of tank ventilators and the physiological effects of negative pressure ventilation (NPV), we summarize the recent application of this old technique in the treatment of acute respiratory failure (ARF). Several uncontrolled studies suggest that NPV may have a potential therapeutic role in the treatment of acute on chronic respiratory failure in patients with chronic obstructive pulmonary disease and restrictive thoracic disorders, reducing the need for endotracheal intubation. In the paediatric field, after substantial technical improvement, NPV has been successfully reintroduced for the treatment of ARF due to neonatal distress syndrome and bronchopulmonary dysplasia, and for the weaning from positive pressure ventilation in intubated patients.The positive results of these reports need to be formally confirmed by further prospective and controlled studies before recommending the generalized use of negative pressure ventilation in acute respiratory failure as a standard of care.