Intracranial pressure and cerebral perfusion pressure in severe head injury.

Monitoring and management of intracranial pressure (ICP) are fundamental to modern neurotraumatology. Although never formally proven to independently improve outcome in prospective, randomized, placebo-controlled trials, there is such a predominance of indirect support for this modality that most neurotrauma protocols are impossible with-out its inclusion and ethical considerations virtually preclude placebo-controlled trials of its efficacy. In addition to the question of improving outcome, ICP monitoring is also useful in guiding the use of potentially harmful treatment modalities such as hyperventilation, mannitol, and barbiturates, and also provides important prognostic data. ICP monitoring provides information on the likelihood of cerebral herniation and allows calculation of the cerebral perfusion pressure (CPP). Although there is no constant threshold for herniation, the most commonly used treatment threshold is 20 to 25 mm Hg. In addition, ICP trends are indispensable in providing the earliest possible indication of critical intracranial mass effects when combined with other clinical indicators. CPP is the difference between mean arterial pressure and ICP. CPP is an important clinical indicator of cerebral blood flow (CBF). Cerebral autoregulation generally remains at least partially preserved after severe head injury, although the CPP value at which it is activated appears to be shifted upward. Therefore, maintaining adequate CBF appears to require using an elevated minimal CPP threshold when treating the injured brain. A generally accepted value of 70 mm Hg is suggested.