Whilst awake, a patent airway is actively maintained.

Gases normally pass to and from the trachea, via a patent upper airway - a partially collapsible structure maintained ‘open’ by muscular tone.

Airway obstruction arises when the nasal and oral passages are obstructed, thereby preventing gas flow.

Partial obstruction arises from lesser degrees of airway obstruction.

Before progressing, consider the question, why does anaesthesia produce the ideal circumstances for airway obstruction? The next page provides the answer.