[Independent compartment phenomena: characteristics of dynamics in cerebral tissue oxygen metabolism under increased intracranial pressure in immature brain: an experimental study].

: The aim of this study is to clarify the specific pathophysiology of increased intracranial pressure in an immature brain in relation to its unique cerebral blood flow dynamics and brain tissue oxygen metabolism. Thirteen puppies were used for an experimental model of brain herniation due to a massive intracerebral hematoma. Along with increasing size of the hematoma, the intracranial pressure (ICP), carotid blood flow (CBF) and cerebral tissue oxygen (CTPO2) were measured simultaneously and continuously. The tolerance capacity for an acutely expanding mass lesion, or intracranial compliance, was studied. The ratio of hematoma volume/body weight was obviously higher by more than 200% in a group of younger puppies with open cranial sutures. Dynamic changes of CTPO2 were noted to be independent in the cerebral subcortical region and the medulla oblongata, when Doppler detection of arterial pulsations showed no flow in the anterior circulation in association with increased intracranial pressure caused by a supratentorial expanding mass lesion. A case with open cranial sutures (1,500 g of body weight) clearly demonstrated this and survived over 24 hours. With acutely increasing ICP CTPO2 was elevated modestly in the cerebral subcortical region (p < 0.1) and prominently in the medulla oblongata (p < 0.005). In conclusion, the posterior fossa structure (brain stem and cerebellum) in the immature age group is protected from an acutely expanding mass lesion in the supratentorial compartment. The posterior fossa behaves as an independent compartment with more prominent CBF and CTPO2 reactivity in the dynamic changes. The author proposed to name these findings as "independent compartment phenomena".