Food, vomit, and the tongue itself can obstruct the airway to the lungs and cause choking. The signs of choking are difficulty breathing and speaking, and sometimes coughing. If the obstruction cannot be removed, the person will turn blue and clutch at the throat, after a minute or so, he or she will become unconscious. Choking while remaining conscious is a frightening experience, but usually the obstruction clears itself before serious harm is done. Clarify whether the person is choking rather than suffering a heart attack or other cause of sudden respiratory distress by asking them.
To begin with, encourage the casualty to cough and remove any obvious obstruction from the mouth. If this does not work, or if the choking person stops coughing and begins to turn blue, bend the body over slightly (or get the person to lie on his or her side) and sharply thump the back between the shoulder blades three or four times using the heel of your hand. If the casualty is a child hold him or her upside down or face-down over your knee and strike with less force. If the obstruction is not dislodged, repeat after a few seconds. This 'shock treatment' usually works even when obstruction is caused by spasm of the muscles lining the windpipe.
If this fails, carry out the Heimlich Manoeuvre (also called the 'abdominal thrust').
Grasp the casualty from behind, tucking one of your fists underneath the breastbone and grasping it with your other hand. Pull sharply inwards, thrusting in and up beneath the breast bone. This produces a sudden increase of pressure in the chest cavity, which should expel the obstruction. Repeat up to five times if necessary.
Repeat the cycle of back blows and abdominal thrusts up to three times if necessary. If the obstruction persists, or if the person becomes unconscious, commence cardio-pulmonary resuscitation, or put the person in the recovery position (see Breathing and Unconsciousness), and contact Emergency Medical Services.
With a child, use just two fingers under the breastbone rather than your whole fist, and pull upwards and inwards more gently. The Heimlich Manoeuvre is itself not without risk. After using it, the casualty should be examined in hospital to make sure no internal damage has been done.