After the FIO2 of mechanically ventilated patients is decreased, 30 minutes or more is often allowed to elapse before follow-up arterial blood gas (ABG) values are obtained. However, waiting this long to assess the PaO2 after an FIO2 reduction may subject the patient to unnecessary hypoxemia. Method: We compared the PaO2 at 10 minutes with that at 30 minutes after we lowered the FIO2 by 0.10 in 17 patients receiving mechanical ventilation. All the patients in our study required mechanical ventilation due to head injury associated with multiple trauma; none had chronic obstructive pulmonary disease (COPD). Results: There was no statistical difference between PaO2 at 10 minutes and that at 30 minutes after the FIO2 reduction (P = 0.39 by Student's paired t test). Conclusion: We conclude that in mechanically ventilated patients who do not have chronic underlying pulmonary disease, ABG values obtained 10 minutes after an FIO2 reduction of 0.10 are valid for the assessment of arterial oxygenation on the new FIO2. (Respir Care 1985;30:1037-1041.)
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