New horizons (Baltimore, Md.)
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Following severe head injury, derangements of the cerebral vasculature and cerebral blood flow (CBF) often occur, rendering the brain at risk of secondary ischemia. Therefore, monitoring of CBF in head-injured patients is considered useful for understanding the pathophysiology and effects of therapy, although such monitoring has not yet become part of routine patient management in most centers. In this article, we review the current research on CBF in head injury. ⋯ Disturbances of cerebrovascular CO2 reactivity and autoregulation appear to be less frequent than previously assumed. However, when present, such derangements do have consequences for therapy, in particular the management of blood pressure and cerebral perfusion pressure. Potential implications for patient management are discussed.
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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. ⋯ 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.
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In patients requiring ICP monitoring, a ventricular catheter connected to an external strain gauge transducer or catheter-tip pressure transducer device is the most accurate and reliable method of monitoring ICP, and enables therapeutic CSF drainage. Clinically significant infections or hemorrhage associated with ICP devices causing patient morbidity are rare and should not deter the decision to monitor ICP. ⋯ These devices are advantageous when ventricular ICP is not obtained or if there is obstruction in the fluid coupling. Subarachnoid or subdural fluid-coupled devices and epidural ICP devices are currently less accurate.
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Failure of high-dose corticosteroid therapy to ameliorate intracranial hypertension or improve long-term neurologic outcome in patients with traumatic brain injury has been shown in several prospective, randomized clinical trials. Additionally, the risk of complications, including elevations in serum glucose levels and gastrointestinal hemorrhage, although relatively low, make routine use of glucocorticoids further unwarranted in head-injured patients.
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Head-injured patients require maintenance of systemic hemodynamics as well as attention to cerebral hemodynamics. Most head-injured patients have increased metabolic oxygen consumption, mild hypertension, and increased cardiac indices. Assessment of regional perfusion, difficult in many patients, includes monitoring of urinary output. In head-injured patients, especially those with multiple injuries, the two most important goals are preservation of cerebral perfusion pressure (mean arterial pressure minus intracranial pressure) and maintenance of systemic oxygen availability (cardiac index times arterial oxygen content).