Shock is the failure of normal peripheral circulation with a fall in blood pressure. The heart rate increases and urine output falls. The skin temperature may be low with shock and the hands and feet often feel cold. The oxygen saturation may also fall. Most importantly, the capillary filling time is prolonged to over 3 seconds.
In early shock the blood pressure may still be normal (compensated shock) although the peripheral perfusion is poor. Later the blood pressure falls (uncompensated shock).