Brenner R P
Neurol Clin. 1985 Aug;3(3):615-31.
The EEG can be very helpful in the evaluation of patients with altered states of consciousness. Diffuse slowing of background rhythms and the presence of triphasic waves suggests metabolic dysfunction, particularly hepatic. Generalized fast activity may be seen in patients with a drug intoxication. Abnormalities, such as PLEDs or focal continual PDA, support a diagnosis of supratentorial lesion, whereas a normal appearing EEG in a comatose patient suggests a brain-stem lesion. In addition, the EEG may reveal that the alteration in consciousness is due to continual epileptic activity without motor manifestations (nonconvulsive status) that had not been suspected. As indicated, certain patterns have prognostic implications. However, as these patterns are not specific for a single etiology, the EEG is of most help when the cause is known. For example, burst suppression or a diffuse alpha pattern coma can be seen in either hypoxia or a drug intoxication. With hypoxia, these patterns carry an extremely poor prognosis for useful recovery, whereas complete recovery is often seen in cases secondary to drug ingestion. As a more extreme example, a patient whose EEG shows ECS secondary to drug intoxication may recover but will not if the ECS is due to hypoxia or severe head trauma. If the etiology of the encephalopathy is unknown, then sequential records are needed for prognosis.
脑电图对意识状态改变的患者评估非常有帮助。背景节律的弥漫性减慢和三相波的出现提示代谢功能障碍，尤其是肝脏方面的。药物中毒患者可能出现广泛性快速活动。诸如周期性一侧性癫痫样放电（PLEDs）或局灶性持续性周期性放电（PDA）等异常支持幕上病变的诊断，而昏迷患者脑电图正常提示脑干病变。此外，脑电图可能显示意识改变是由于未被怀疑的无运动表现的持续性癫痫活动（非惊厥性癫痫持续状态）所致。如前所述，某些脑电图模式具有预后意义。然而，由于这些模式并非单一病因所特有，当病因已知时脑电图最有帮助。例如，爆发抑制或弥漫性α波昏迷模式在缺氧或药物中毒时均可出现。对于缺氧情况，这些模式提示有效恢复的预后极差，而药物摄入所致病例通常可完全恢复。更极端的例子是，脑电图显示由药物中毒引起的电静息（ECS）的患者可能恢复，但如果ECS是由缺氧或严重头部外伤所致则不会恢复。如果脑病的病因不明，则需要连续记录脑电图以判断预后。
