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The supine patient is at risk of airway obstruction from two routes:
Mechanical obstruction: In this instance, a physical object obstructs the airway of the patient. In most cases this is the patient's own tongue, as the unconsciousness leads to a loss of control causing the tongue to fall to the back of the pharynx, creating an obstruction. This can be controlled (to an extent) by a trained person using airway management techniques

Fluid obstruction: Fluids, usually vomit, can collect in the pharynx, causing the person effectively to drown. The loss of muscular control which causes the tongue to block the throat can also lead to the stomach contents flowing into the throat, called passive regurgitation. Fluid which collects in the back of the throat can also flow down into the lungs. Another complication can be stomach acid attacking the inner lining of the lungs

First aid organisations were similarly slow in adopting the idea of the recovery position, with 1930s and 1940s first aid manuals from the British Red Cross and St John Ambulance both recommending lying a patient on their back. The First Aid Manual goes so far as to instruct "place the head in a such as position that the windpipe is kept straight, keeping the head up if the face is flushed, and in line with the body if it is pale".   turning the head to the side, added "if breathing is noisy (bubbling through secretions), turn the patient into the three-quarters prone position"


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