Severe crush injuries cause extensive damage to skin, muscle, nerves and bone. There may be internal and external bleeding, or blood supply to a limb may be cut off for some time. Large quantities of plasma may leak from the blood vessels into the damaged tissues, causing swelling and Shock. When the crushed part is released, toxic chemicals produced by damaged muscles get into general circulation, leading to kidney failure in severe cases.
If the crushed part has been trapped for more than 30 minutes, do not attempt to release the casualty before medical help arrives. If release is immediate, raise the affected limb, but keep the victim still. Try to prevent bleeding, dial 911, and give as much comfort and reassurance as you can.
Minor crush injuries, such as slamming a finger in a car door or dropping a hammer on a toe, hurt because of the high concentration of nerve fibres in the extremities.