Anesthesia for patients with neurologic disease.

Cerebral blood flow may be altered in anesthetized patients, and this could be detrimental to patients with intracranial disease. Cerebral blood flow is autoregulated and held constant over a mean arterial pressure range of 50 to 150 mm Hg. Changes in cerebral blood volume are reflected by cerebral blood flow, whereas intracranial pressure varies directly with cerebral blood volume. Cerebral blood flow is also under chemical regulation and varies directly with arterial carbon dioxide tension over the range of 25 to 70 mm Hg. A reduction in arterial oxygen tension to below 60 mm Hg also dramatically increases cerebral blood flow. Changes in both arterial carbon dioxide and oxygen tensions are common in anesthetized patients. Furthermore, anesthetic drugs can alter cerebral blood flow. Injectable anesthetics, except ketamine, tend to preserve cerebral blood flow. Inhalant anesthetics may be associated with cerebral vasodilation, increased cerebral blood flow, and raised intracranial pressure. However, low concentrations of inhalant anesthetics combined with controlled ventilation are effective in preventing exacerbation of raised intracranial pressure. Factors affecting cerebral blood flow should be considered before anesthetizing patients with intracranial disease.