Effect of hypoxia on traumatic brain injury in rats: Part 1. Changes in neurological function, electroencephalograms, and histopathology.

The effect of hypoxia on neurological function, compressed spectral array electroencephalography, and histopathology in head-injured rats was evaluated. By itself, an hypoxic insult (PaO2, 40 mm Hg for 30 minutes) caused no neurological deficit. Twenty per cent of rats injured by a 5-atmosphere temporal fluid percussion impact were hemiparetic contralateral to the side of impact, whereas 80% had no deficit 24 hours after injury. Seventy per cent of rats with both fluid impact injury and hypoxic insult, however, either had a definite hemiparesis, showed no spontaneous movement, or died (P less than 0.02). Impact alone produced an initial depression in electroencephalogram power that was prolonged in rats with hypoxic insult; the most dramatic effect was found in the injured hemisphere, with shorter and less profound effects in the contralateral hemisphere. Perfusion staining of injured cerebral tissue in vivo with 2,3,5-triphenyltetrazolium chloride showed an area of extensive ischemia around the impact site in rats with hypoxic insult. This ischemic area was not present in rats with either impact injury or hypoxia alone. We conclude that posttraumatic hypoxia clearly increases the severity of impact injury in this rat model. These findings suggest that hypoxia, which is common in head-injured patients, very likely worsens the effect of impact injury and may account for much of the diffuse neurological dysfunction in patients with severe craniocerebral trauma.