A medical emergency is an injury or illness that is acute and poses an immediate risk to a person's life or long term health. These emergencies may require assistance from another person, who should ideally be suitably qualified to do so, although some of these emergencies can be dealt with by the victim themselves. Dependent on the severity of the emergency, and the quality of any treatment given, it may require the involvement of multiple levels of care, from a first aider to an emergency physician through to specialist surgeons.
Any response to an emergency medical situation will depend strongly on the situation, the patient involved and availability of resources to help them. It will also vary depending on whether the emergency occurs whilst in hospital under medical care, or outside of medical care (for instance, in the street or alone at home).
For emergencies starting outside of medical care, a key component of providing proper care is to summon the emergency medical services (usually an ambulance), by calling for help using the appropriate local emergency telephone number, such as 999, 911, 112, 000 or 111. After determining that the incident is a medical emergency (as opposed to, for example, a police call), the emergency dispatchers will generally run through a questioning system such as AMPDS in order to assess the priority level of the call, along with the caller's name and location.
Those trained to perform first aid can act within the bounds of the knowledge they have, whilst awaiting the next level of definitive care. Those who are not able to perform first aid can also assist by remaining calm and staying with the injured or ill person. A common complaint of emergency service personnel is the propensity of people to crowd around the scene of victim, as it is generally unhelpful, making the patient more stressed, and obstructing the smooth working of the emergency services. If possible, first responders should designate a specific person to ensure that the emergency services are called. Another bystander should be sent to wait for their arrival and direct them to the proper location. Additional bystanders can be helpful in ensuring that crowds are moved away from the ill or injured patient, allowing the responder adequate space to work.
Many states of the USA have "Good Samaritan laws" which protect civilian responders who choose to assist in an emergency.<ref>E.g., Virginia Code § 8.01-225.</ref> Responders acting within the scope of their knowledge and training as a "reasonable person" in the same situation would act are often immune to liability in emergency situations. Usually, once care has begun, a first responder or first aid provider may not leave the patient or terminate care until a responder of equal or higher training (e.g., fire department or emergency medical technicians) assumes care. This can constitute abandonment of the patient, and may subject the responder to legal liability. Care must be continued until the patient is transferred to a higher level of care, the situation becomes too unsafe to continue, or the responder is physically unable to continue due to exhaustion or hazards.
The principles of the chain of survival apply to medical emergencies where the patient has an absence of breathing and heartbeat. This involves the four stages of Early access, Early CPR, Early defibrillation and Early advanced life support
Unless the situation is particularly hazardous, and is likely to further endanger the patient, evacuating an injured victim requires special skills, and should be left to the professionals of the emergency medical and fire service.
Within hospital settings, an adequate staff is generally present to deal with the average emergency situation. Emergency medicine physicians have training to deal with most medical emergencies, and maintain CPR and ACLS certifications. In disasters or complex emergencies, most hospitals have protocols to summon on-site and off-site staff rapidly.
Both emergency room and inpatient medical emergencies follow the basic protocol of Advanced Cardiac Life Support. Irrespective of the nature of the emergency, adequate blood pressure and oxygenation are required before the cause of the emergency can be eliminated. Possible exceptions include the clamping of arteries in severe hemorrhage.
While the golden hour (medicine) is a trauma treatment concept, two emergency medical conditions have well-documented time-critical treatment considerations: stroke and myocardial infarction (heart attack). In the case of stroke, there is a window of three hours within which the benefit of clot-busting drugs outweighs the risk of major bleeding. In the case of a heart attack, rapid stabilization of fatal arrhythmias can prevent sudden cardiac death. In addition, there is a direct relationship between time-to-treatment and the success of reperfusion (restoration of blood flow to the heart), including a time dependent reduction in the mortality and morbidity.