Oxygen toxicity in rats. Varied effect of dexamethasone treatment depending on duration of hyperoxia.

The low rate of survival in patients with the adult respiratory distress syndrome (ARDS) may in part reflect a failure to consider that the lung's response to applied therapies may not be constant throughout the course of illness. To test this notion, we used hyperoxia to produce progressive lung damage in rats and administered dexamethasone at different times during O2 exposures of various lengths. Dexamethasone improved survival and decreased lung damage if given when exposure to hyperoxia was to be soon terminated; pulmonary inflammation was marked at the time at which the administration of dexamethasone led to increased survival. Dexamethasone worsened lung damage and diminished survival when given early during exposure to hyperoxia; inflammation was minimal early in the course of exposure to hyperoxia. These findings point to the need for a more analytical approach to research on therapy of ARDS; agents that are harmful at one time may be beneficial at another time.