A quantitative study of some factors affecting the outcome of experimental epidural bleeding in swine

During an experimentally induced aggressive epidural bleed the effect on outcome of haematoma volume, cerebral perfusion pressures, intracranial pressure gradients and ventilation were examined in a swine model. Two groups of experiments were performed using either spontaneous ventilation (group 1, n = 6) or mechanical ventilation for 1 hour (group 2, n = 7). The preparations were otherwise identical. An animal was considered to have succumbed when the EEG became irreversibly isoelectric within a total follow-up time of 80 minutes. Mechanical ventilation had a marked effect on survival. All spontaneously ventilated animals succumbed, 4 of them in less than 60 minutes, the remaining 2 between 60 and 80 minutes after the start of bleeding. All mechanically ventilated animals survived for the 60 minutes while the ventilator was connected. Following disconnection 2 animals started to breathe spontaneously and survived the final 20 minutes of the 80 minutes of the follow-up time. The remaining 5 succumbed following apnoea. The size of haematoma did not differ significantly between the groups. Two additional factors, hypoventilation and a secondary rise in supratentorial pressure, contributed to a lethal outcome. Hypoventilation was an inevitable precursor of the isoelectric EEG. There was a close correlation between the development of hypoventilation and intracranial herniation. A secondary rise in supratentorial pressure, unrelated to ventilation, was seen after cessation of bleeding in 8/13 cases. It was associated with a falling supratentorial perfusion pressure and EEG attenuation, suggesting a secondary intracranial expansion, possibly due to oedema, hydrocephalus or both. It is concluded that mechanical ventilation in the acute stage of epidural bleeding may be of clinical value.(ABSTRACT TRUNCATED AT 250 WORDS)