Is 50% oxygen harmful?

Pulmonary gas exchange after tracheal extubation was evaluated in 25 patients to determine the effect of 50% oxygen administered during mechanical ventilation following aortocoronary bypass grafting. Twenty-five patients postoperative mechanical ventilation for 16-24 hr, 13 with an inspired oxygen fraction (FIO₂) of no more than 0.30 and 12 with an FIO₂ of 0.50. After tracheal extubation, all patients spontaneously breathed room air (FIO₂ 0.21). Postextubation the calculated venous admixture of patients who had received 50% oxygen (0.20 ± 0.03 [SD]) was significantly (p < .01) greater than that calculated for patients who received lower oxygen concentrations (0.13 ± 0.04). Consequently, the PaO₂ of patients who had received 50% oxygen (60 ± 5 torr) was significantly (p < .03) lower than the PaO₂ of patients who had received no more than 30% oxygen (66 ± 7 torr). Thus, administration of 50% oxygen, supposedly nontoxic, to mechanically ventilated patients may cause impairment of pulmonary gas exchange after tracheal extubation. Although high concentrations of supplemental oxygen are sometimes required, unnecessary elevation of FIO₂ is not likely to significantly increase oxygen delivery and may contribute to postextubation pulmonary dysfunction.