大量伤患事件（Mass casualty incident、Multiple casualty incident，简称MCI），以字面上解读是指单一事件的发生会同时产生许多位需要急救的伤患，也就是说同一事件所造成大量患者就诊。就定义而言，可区分成「事件」、「紧急状况」、「灾难」三种，事件则比如火灾事件、交通事故、建筑物倒塌，紧急状况则是因为社会或整个国家遭逢巨变而处于难以应变的状况，灾难是指人为造成或自然发生而直接冲击到社会或整个国家所导致的严重损失。无论哪一种定义，一旦事件的发生可足以造成危及整个医疗体制之正常运作，不但冲击到院内病人的医疗品质，也直接威胁到这起事件造成的大量伤患送至医院急救之权益，严重进而死亡所引发二次灾害，因此必须有一套完善的大量伤患机制，可在短时间内应付这些大量伤患。当事件现场的发生会依灾情做适合的判断，并交由政府设立的指挥中心掌握权限，如灾情与整个社会或国家涉及层级有达到严重等级，必须启动大量伤患机制，将全数的医疗人员以紧急召集方式快速返回医院内职位进行急救，这些医疗人员包括医院内任职的行政人员、聘雇人员以及在国外的各人员。

A mass casualty incident (often shortened to MCI and sometimes called a multiple-casualty incident or multiple-casualty situation) is any incident in which emergency medical services resources, such as personnel and equipment, are overwhelmed by the number and severity of casualties. For example, an incident where a two-person crew is responding to a motor vehicle collision with three severely injured people could be considered a mass casualty incident. The general public more commonly recognizes events such as building collapses, train and bus collisions, earthquakes and other large-scale emergencies as mass casualty incidents. Events such as the Oklahoma City bombing in 1995 and the September 11 attacks in 2001 are well-publicized examples of mass casualty incidents.