Rate of Decay or Increment of PaO2 Following a Change in Supplemental Oxygen in Mechanically Ventilated Patients With Diffuse Pneumonia

It has been shown that patients with COPD require as long as 20 min for equilibration of oxygen tension to occur after changing the fraction of inspired oxygen (FIO 2 ). To date, there have been no studies to determine the equilibration tune for the PaO 2 in mechanically ventilated patients with diffuse pneumonia. We studied seven patients (five males, two females) with radiographic evidence of diffuse pneumonia. All patients required mechanical ventilation. After introducing a change in FIO 2 , arterial blood gas values were measured at 5-min intervals for 30 min. Four patients achieved maximal change in PaO 2 after 5 min, while four patients required 10 min. These results are similar to those found in patients with left ventricular failure who experience equilibration rapidly; however, patients with COPD experience it at a much slower pace. These observations have clinical importance when managing unstable patients where time is a critical element.