In emergency medicine, ensuring the airway is not obstructed is usually the first priority in assessment and immediate measures.  The mnemonic “ABCD” gives the immediate priorities:
Airway: There must be a clear path from the nose or mouth to the lungs, which may take no more than proper anatomic positioning with the head tilt/chin lift maneuver. Even if the patient is incapable of active breathing, air can be supplied externally, but if there is no way to oxygenate the blood, irreparable brain damage can start in 4 5 minutes at normal body temperature. It may be necessary to establish an artificial airway with intratracheal intubation or cricothyrotomy 
Breathing: If the patient is making no respiratory effort, oxygen converse shoes can be supplied externally, initially by mouth to mouth artificial respiration, manual bag valve mask device, or a mechanical ventilator. When the patient is breathing ineffficiently, supplemental oxygen may be adequate, or it may be necessary to paralyze the respiratory muscles and take over mechanical ventilation.
C:irculation. Blood needs to move, through regular or artificial heartbeat, or interventions to restore circulation.
D:efinitive. Urgent interventions to deal with the specific pathology, such as drugs or defibrillation
Whenever there is even mild respiratory distress, emergency personnel must plan for contingencies; some conditions, such as anaphylactic shock can progress from itching and wheezing, to complete airway obstruction, in minutes.
If there is active respiratory distress or a strong index of suspicion that it is imminent, other supportive steps should be taken. A breathing patient should be put on oxygen. Establish at least two large bore intravenous lines, draw several tubes of venous blood according to the local protocol, and attach the patient to a cardiac monitor defibrillator.
Attach a pulse oximeter, and, when available and especially if an airway inserted, a capnography sensor. Take vital signs.
Position the patient to assist respiration. The examiner begins by a converse shoes ssessing the patient’s level of consciousness and efficiency of breathing. If the patient is conscious, able to speak, not cyanotic, and has nonemergent vital signs and chest sounds, assessment can proceed to the evaluating urgent but not immediately life threatening conditions. 
In a nonbreathing patient, the simplest and fastest measures may be all that is needed: the head tilt/jaw li converse shoes ft maneuver. This is contraindicated if there is there is suspe converse shoes cted injury to the cervical spine, and the jaw thrust maneuver used instead. If head tilt/jaw lift fails, jaw thrust sometimes restores the airway. Should the circumstances suggest the airway might be obstructed by a foreign body, including food, perform an age appropriate airway clearing procedure such as infant back blows or the Heimlich maneuver.
If those manual maneuvers fail, the next actions depend on the training of the responder and the available equipment. Soft rubber or plastic nasopharyngeal or oral airways may be used before more advanced methods, and, if available, positive pressure ventilation may be tried briefly before moving to more advanced measures such as intubation or creating a surgical airway. Some conditions justify immediate intubation: 
No breathing at all (apnea)
Glasgow Coma Scale Sustained seizure activity.
Large flail segment or respiratory failure.
High aspiration risk.
Inability to otherwise maintain an airway or oxygenation. physically protects the airway from vomitus or other fluids being aspirated, and also acts as a mechanical “splint” inside it, protecting it from laryngospasm or laryngeal edema. While clinical judgment is always paramount, full endotracheal intubation may not be needed. Various less invasive oral or nasopharyngeal airway may provide adequate mechanical support, and require far less less technical skill to insert.