In those patients receiving TT02 therapy who demonstrated increases in Pa02 to levels above 55 mm Hg, the initial arterial oxygen tensions were between 50 and 54 mm Hg; however, in two of three patients who showed similar improvement in the study of Weitzenblum et al, the initial Pa02 was 43 and 48 mm Hg, respectively. Since all patients in the TTOa study had already been receiving oxygen therapy by nasal cannula, the reduction in P(A-a)02 observed may be a result of better compliance with therapy (continuous oxygen) and tighter control of arterial oxygen saturations.
The NOTT study demonstrated that nearly continuous oxygen therapy (approximately 19 h/day) resulted in improved survival when compared with oxygen therapy for only 12 or 15 hours each day. It is quite possible that uninterrupted oxygen therapy for 24 hours each day by a transtracheal catheter may have additional therapeutic benefit. Also, all patients receiving TTO2 had oxygen therapy adjusted for both rest and exercise to assure adequate arterial oxygen saturation throughout the day, a procedure not routinely done when nasal oxygen therapy is prescribed.