The Effect of Intermittent. Negative Pressure Ventilation and Long-term Oxygen Therapy for Patients With COPD – Discussion
Long-term oxygen therapy has been shown to improve the quality of life and the length of survival of patients with COPD with hypoxemia, even though this form of treatment does not seem to arrest the course of the underlying airway disease. Recendy, Cooper and Howard studied a series of 35 patients with COPD receiving LTOT and observed a worsening of FEVj before death despite the administration of oxygen. This observation suggests that oxygen therapy is ineffective in arresting the progression of the disease and that patients with low FEVj values at the commencement of LTOT are therefore likely to receive a limited benefit from oxygen. Long-term oxygen therapy is generally recognized to improve survival in patients with COPD who present with an acute exacerbation treated with mechanical ventilation. To our knowledge, however, no specific data supporting this conclusion have been published.
To address this issue, we evaluated the prognosis in 35 patients who presented with an episode of ARF and who were treated with INPV during the acute phase, and then with long-term home oxygen therapy (treatment group). We compared these 35 patients with a control group of 44 patients from our institution who received the same yentilatory treatment in the acute phase and no LTOT thereafter. The main finding resulting from our study is that the survival rate of the treatment group was significantly better than that of the controls (Fig 1 and Table 2). It should be stressed that this survival comparison involved two groups of patients who were all treated with INPV during the acute phase and in whom the possible beneficial effects of this therapeutic intervention were therefore shared.
The better survival found in our treatment group could be attributed, at least in part, to the effects of LTOT. As a result, our data indicate that LTOT for more than 15 h/d seems to improve survival, for at least 2 to 4 years, in patients with COPD who need intermittent mechanical ventilation for ARF. Interestingly enough, the significant difference in survival favoring our treatment group was observed despite the fact that these patients had a more marked degree of bronchial obstruction and a more severe hypoxemia and hypercapnia.
In a previous study of patients with COPD treated with LTOT, the values of Pa02 were found to decrease at a rate of 0.47 ± 0.01 kPa (3.52 ± 0.075 mm Hg) per year while the values of PaCO;y2 increased by 0.25 ± 0.09 kPa (1.875 ± 0.675 mm Hg) per year. Over the 3 years preceding death, an acceleration was observed in both the decrease of Pa02 and the increase of PaC02. In the MRC trial, similar changes in Pa02 and PaC02 were found in patients with COPD receiving LTOT who died early.