暈厥是一種症狀，通常是短暫性、自限性意識喪失，導致昏倒。它的發作相當快速，自 發性意識恢復立即且完全。暫時性大腦的缺乏灌注是主要機轉。而大腦灌注壓力大部分取決 於收縮壓。因此，任何因素導致心輸出量降低或全身血管阻力降低，導致血壓及大腦灌注壓 力下降皆有可能導致暈厥。以心輸出量而言，最重要的生理決定因子是靜脈充填。因此過多 的血液存於下肢或是減少液體體積將會加重暈厥。若以末梢血管阻力而言，廣泛性的以及過 度的血管擴張在降低動脈壓扮演關鍵角色。傾斜床試驗顯示收縮壓一旦低於60 mmHg就會伴 隨暈厥。因此血壓的控制機轉是維持大腦營養輸送之要件，它包括(a)大腦血管自動控制之能 力；(b)局部新陳代謝及化學控制來允許大腦血管擴張；(c)動脈血壓接受體來調節心跳、收縮 力及全身血管阻力。本篇論文旨在探討暈厥的診斷及處理的最新建議及治療。包括暈厥的分 類，流行病學及預後。診斷及治療和特殊暈厥事件，雖然本文涵蓋各方面的暈厥，但主要的， 我們仍專注於下列(1)暈厥原因診斷要件(2)何者是最適宜的診斷(3)如何區分出有危險性的病 人(4)暈厥病人應何時入院？(5)預防暈厥的再犯，何種治療為最有效方式。一旦評估完成， 而且無任何原因，則再度評估每項細節是必需的；因為一些細微易忽略之徵象或是新的病歷 資訊都有可能完全改變其鑑別診斷。若是線索直指心臟或神經疾患原因，則此方面的評估無 疑是必需的；另外諮詢心血管或神經各科專家是必要的。

onset of syncope is relatively rapid and the subsequent recovery is spontaneously complete and prompt. Transient global cerebral hypoperfusion is the underlying mechanism. Cerebral perfusion pressure is largely dependent systemic arterial pressure. Thus, any factor that decreases either cardiac output or to-tal peripheral vascular resistance diminishes systemic arterial pressure and cerebral perfusion pressure. In terms of cardiac output, the most important physiological determinant is venous filling. Therefore, excessive pooling of blood in dependent parts of the body or diminished blood volume may predispose to syncope. With regard to peripheral vascular resistance, widespread and excessive vasodilatation may play a critical role in decreasing arterial pressure. Experience from head-tilt testing showed that a decrease in systolic blood pressure (SBP) to 60 mm Hg is associated with syncope. In this regard, the integrity of a number of control mechanisms is crucial for maintaining adequate cerebral nutrient delivery, including: (a) cerebrovascular auto-regulatory capability; (b) local metabolic and chemical; (c) arterial baroreceptor - induced adjustments of heart rate, contractility, and systemic vascular resistance; and (d) vascular volume regulation.The purpose of this review article is to provide specific notice and recommendations on the diagnostic evaluation and management of syncope.We also focused on the following main issues as follows: (1) what are the diagnostic criteria for causes of syncope? (2) What is the preferred approach to the diagnostic work-up? (3) How should patients with syncope be risk stratified? (4) What should patients with syncope be hospitalized? (5) Which treatments are likely to be effective in preventing syncopal recurrence? Once the syncopal evaluation is completed and no cause of syncope is determined, reappraisal of the work-up is needed since subtle findings or new historical information may change the entire differerential diagnosis. If unexplored clues to possible cardiac or neurological disease are apparent, further cardiac and neurological assessment is recommended. In these cir-cumstances, consultation with appropriate specialty may be warranted. ( J lntern Med Taiwan 2010; 21: 90-108 )