Abstract
In recent years, patients with various respiratory disturbances to be treated with artificial ventilation for prolonged period have been increasing in number. In such case, the decision for adequate tidal volume and O2 concentration is the most fundamentally important factor, but the effect of artificial ventilation to the central nervous system must be considered. We discussed in this paper the effect of prolonged artificial ventilation with O2 to brain.
Adult cats were used for experimental animals. Systemic BP, ICP, EEG and ECG were monitored and recorded under artificial ventilation with room air or pure O2, and arterial blood gas was analyzed intermittently. When animals sacrificed, the brain was irrigated with barium-gel. Sections were made for histopathological examination, and soft X-ray for microcirculation.
Pure O2 inhaled animals showed ICP increase and elevation of systemic BP within 24 hours. In fetal cases, pressure wave phenomenon was observed within 48 hours, i.e., acute brain swelling was developed. The mortality rate of this group was 67%.
On the contrary, room air animals showed ICP and BP were stabilized until the termination of the experiments.
The examination for microcirculation in pure O2 animals revealed severe circulation disturbance and decrease of capillaries in number in all animals. Histological examination revealed pathological changes in whole brain; degeneration of neurones, gliosis, demyelination, disruption and swelling of axons, and vacuolations. Especially on the cerebellum, degeneration of Purkinje' cells and status spongiosus in granular layer were observed.
At this time, we cannot clearly explain the pathological effect of O2 to brain, but prolonged artificial ventilation with highly concentrated O2 is responsible for the development of such severe condition by the tissue toxicity or vasoconstriction of O2.
