Ideally, suction should be used to remove secretions, mucous, or blood from the airway or oropharynx when establishing and maintaining an airway. The JTS clinical practice guidelines characterize suction devices as:
Preoxygenate the casualty before suctioning (if possible) for a minimum of 30 seconds and to limit the suction time to NO more than 10 seconds to prevent hypoxia. Also, insert the suction catheter no further than you can visualize, or you may stimulate a gag reflex.
Of note, the suction should only be applied when withdrawing the catheter and not upon initial insertion.