Only 77 of 117 subjects who entered the study completed the three-month trial period. Seventy-five percent of the 40 patients who failed to complete the three-month trial period did so because they refused repeated arterial punctures, their disease worsened during the period of observation, they were withdrawn by their physicians for ethical reasons, they died, or they were unavailable for follow-up. These data suggest that withholding oxygen therapy for three months may have had a detrimental effect on some patients. The authors recommended that the period of assessment for clinical stability should be a minimum of one month and preferably two to three months when the initial Pa02 ranged from 50 to 60 mm Hg.
The beneficial effects of oxygen as a drug must also be considered in evaluating a patients response to therapy and in assessing improvements seen in ABG measurements. The mortality of patients with COPD appears to be greatest when hypoxemia and pulmonary hypertension are present, and LTOT definitely increases survival; yet, studies have not confirmed the correlation between reduction in Ppa and improved survival. Weitzenblum et al demonstrated in a prospective study that oxygen therapy results in a modest reduction in Ppa and, perhaps more importantly, appears to have a significant effect in reducing the progression of pulmonary hypertension.