Intérêt de la différence aterio-veineuse en O2 dans l'approche thérapeutique de l'hypertension intracrânienne post-traumatique

Elevated intracranial pressure (ICP) is undoubtedly a determinant factor of outcome in severe head injured patient. Until now, medical treatment of elevated ICP in diffuse brain lesions consisted of hyperventilation, CSF drainage, mannitol and barbiturates without accurate selection criteria. In fact, in comatose patients, the cerebral blood flow (CBF) can vary independently of the cerebral metabolic rate of oxygen (CMRO2) which is typically reduced. The venous oxygen saturation (SjO2) measured in the jugular bulb and the arterial-jugular oxygen difference (ajDO2) can be used for more appropriately selecting therapeutic measures. According to the following equation: CMRO2 = CBF x ajDO2, the measurement of the changes in ajDO2 might serve as an indicator of CBF adequacy, out of the presence of cerebral ischemia. A decreased ajDO2 suggests that CBF is excessive for cerebral metabolic requirements and an elevated ajDO2 indicates a decreased CBF. Consequently, treatment of elevated ICP in the presence of a low ajDO2 should be more oriented towards moderate hyperventilation and administration of metabolic depressive agents with maintenance of normal arterial blood pressure. Conversely, in case of high ajDO2, ICP control should aim to increase CBF by maintaining normocapnia, improving hemodynamic status or reducing extravascular volume accordingly.