Changes in CSF pressures during experimental acute arterial subdural bleeding in pig

The effects of acute arterial subdural bleeding on cerebrospinal fluid (CSF) pressure and 12 other vital parameters were studied in spontaneously breathing pigs (group 1, n = 9) and in mechanically ventilated pigs (group 2, n = 18) to analyze quantitatively the bleeding course and the lethal mechanism. Spontaneously breathing animals all succumbed after a mean bleeding volume of 45.6 +/- 8.9 ml, corresponding to about 50 per cent of the intracranial volume, and a mean bleeding duration of 11.0 +/- 2.6 min. Rapid rise in CSF pressures, marked transtentorial pressure gradients, and progressive reductions of cerebral perfusion pressure leading to a permanently iso-electric EEG, apnoea and to a terminal rise in arterial pressure (Cushing response), was the rule in these animals. The mechanically ventilated animals had smaller bleeding volumes (34.3 +/- 8.1 ml), but longer bleeding durations (13.8 +/- 5.8 min). In this group 7 animals survived. They had no pressure gradients, and only moderate changes in arterial pressure and EEG. The 11 animals that succumbed had marked transtentorial pressure gradients, but smaller increments in arterial pressure than the spontaneously breathing animals. At autopsy, subdurally located blood was found throughout the intracranial and spinal subdural compartments and along the spinal nerve roots in both groups. The results of this study suggest that survival after acute subdural haematoma is influenced by the presence of transtentorial pressure gradients and by the spinal sac acting as a space for expansion. The beneficial effect of artificial ventilation is discussed.