Shock is a physiological reaction by the body to a general lack of oxygen in the body's tissues that can be the result of a number of causes, such as respiratory arrest, severe blood loss, severe traumatic injury (such as from a gunshot wound or loss of limb) or severe pain. In shock, the heart rate rises precipitously while blood vessels in the body constrict, concentrating the flow of blood to vital organs such as the heart, lungs and brain. However, at the same time, blood pressure drops to prevent further bleeding. While this has the temporary effect of preserving the major organs, if left untreated it will eventually overwhelm the body and cause the death of the patient even if the underlying cause of the injury is treated.
Shock is very common in traumatic accidents, such as severe gunshot wounds or automobile accidents. An shocked patient will have cold clammy skin due to the lack of blood to the peripheral parts of the body, will lose consciousness, and may go into convulsions. This can happen even when the injuries are not immediately life threatening. In such cases, it is vitally important to keep the patient's body temperature normal (shielded from extremes of heat and cold), to keep them comfortable, and to ensure that the patient is not losing blood.
Once the physical reaction of shock starts to begin, it tends to make itself worse over time as the physiological effects of the initial shock results in further reactions that make the reactions even more severe. As such, immediate treatment is needed.
Before the development of anesthetics, shock was a major complication of surgery, such as amputation. An amputation that took too long to complete would most likely result in the death of the patient from shock even if blood loss were stemmed immediately after the surgery.