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From Citizendium, the Citizens' Compendium
- 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 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.
Position the patient to assist respiration. Note the patient's weight if the treatment table is equipped with a scale; increasing weight can be a warning of developing pulmonary edema or other fluid load abnormalities.
Immediate airway management
Without a patent airway, all other resuscitative efforts will be futile. The examiner begins by assessing 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-lift maneuver. This is contraindicated if there is there is suspected 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 < 9
- Sustained seizure activity.
- Unstable mid-face trauma.
- Airway injuries.
- Large flail segment or respiratory failure.
- High aspiration risk.
- Inability to otherwise maintain an airway or oxygenation.
Intratracheal intubation 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.
- Rapid sequence intubation
Managing intubated patients in the ER
Other immediate threats to life
Upper airway obstruction
If the Heimlich or related maneuvers fail to remove a foreign body, the next step is attempted removal under direct removal with a laryngoscope. If that fails, a surgical airway is probably necessary, with the understanding that an obstruction in the distal glottis may not be relieved even by cricothrotomy or tracheostomy. Continuing failure requires either a more extensive surgical approach or use of a rigid bronchoscope.
Tension pneumothorax is far more severe than ordinary pneumothorax. In a conventional pneumothorax, air enters the chest cavity, which is normally at negative pressure relative to room air. In the less complicated types of pneumothorax, there is leakage in both directions. Tension pneumothorax, however, is caused by damage that creates a one-way valve effect, so the air pressure in the chest continues to increase, and can cause complete lung failure.
There is considerable controversy about its diagnosis and treatment, especially in the field. In principle, a large-bore hypodermic needle, equipped with a flutter valve that will let air out but not in, converts the condition to a regular pneumothorax. If the problem is indeed tension pneumothorax, and the needle is inserted in the correct place, the decompression can indeed be a lifesaving immediate intervention.
Diagnosis is not as clear-cut as textbooks sometimes suggest, and, in inadequately trained hands, the needle either may not reach the air pocket, or may damage other structures.
Acute Respiratory Distress Syndrome
Acute Respiratory Distress Syndrome is not an independent cause of disease, but a pattern of responses to severe insult to the lungs, from factors including infection in the blood or lungs, or trauma to the lungs. Its presentation includes dyspnea, profound hypoxemia, decreased lung compliance, and diffuse bilateral infiltrates on chest X-ray. There has been an informal concept called the "Golden Hour" in trauma, which, when expressed somewhat more specifically, deals with the increasing probability that massive blood loss will produce "irreversible shock". A less quantitative version of the idea originated in the First World War; a seminal paper from the 1960s quantified, that dogs could survive a loss of 40 to 50 percent of their blood volume if it were replaced within one hour. With each hour of delay in replacement, survival dropped. 
The longer it takes to reverse the pattern presented by ARDS, the less the chance of patient survival. For example, prolonged ARDS can produce pulmonary edema.
Severe aspiration into the respiratory tract
When vomitus is visible in the oropharynx, assume it has been aspirated. Mechanical aspiration problems may result from ingestion of oil or gasoline can also have similar effects.
Before intubation, clear the airway with a suction catheter. Corticosteroids have been shown to decrease recovery and should not be administered. Hospitalize for close monitoring, although the emergency assessment should continue to determine a continuing source of vomiting, or other disturbance to respiration.
While it is not part of the immediate workup, the next stage of the examination must determine if aspiration pneumonia is present. This can be produced by gastric acid, bacteria, or oil.
Severe pulmonary edema
Pulmonary edema can be due to direct lung disorders, or a consequence other disorders of fluid handling, especially heart failure. Cardiac etiology is most common, but primary lung disorders need specific handling; it is not impossible to have comorbid causes, such as ARDS.
There is a syndrome of high-altitude pulmonary edema, which results from exposure to a pressure level approximately of 2.5 km or higher. Obviously, this should be considered in mountainous area, but it is a possible effect of a malfunctioning aircraft oxygen system, and should be considered when an individual develops respiratory distress in flight. Commercial aircraft cabins are pressurized to well below that level, so an isolated case on a passenger aircraft is unlikely, but certainly within the scope of the differential diagnosis if the patient was on a breathing mask in a smaller or military aircaft.
Asthma is, when acquired, usually a lifelong disease. The standard of treatment is to suppress the hyperimmune response, which, through the release of inflammatory factors, will lead to increasing difficulty. Criteria for an immediate asthmatic crisis include an inability to speak and intense perspiration. If the patient has difficulty in speaking and still has trouble breathing when in an optimal resting position, consider the exacerbation as severy. According to the diagnostic criteria of the U.S. National Asthma Education and Prevention Program. Severe asthma has dyspnea at rest and can speak only with difficulty. The peak expiratory flow rate <40 percent predicted or personal best. The situation is Life threatening when respiratory distress makes it impossible to speak, the patient is perspiring, and the peak expiratory flow rate, if it can be taken, is <25 percent predicted or personal best.
Laryngeal or tracheal narrowing
These sections of the upper airway can constrict briefly (laryngospasm) as a muscular effect, or narrow due to local edema. Regardless of the cause, it is obviously urgent to intubate, or, if necessary, establish a surgical airway.
If due to anaphylaxis, or strong suspicion of it, epinephrine should be administered as soon as possible. Patients with known sensitivities that may cause anaphylaxis often may carry autoinjectors; seeing one on or near the patient is strongly suggestive of the condition.
Angioedema involving the respiratory is an uncommon but recognized side effect of angiotensin-converting enzyme inhibitors.
Severe chronic obstructive pulmonary disease
Urgent threats to life
Chest wall defects
Chest wall defects due to trauma often overlap with lung collapse. For example, an extensive rib fracture could simultaneously cause flail chest, a pneumothorax where one broken bone went through the skin, and perhaps hemothorax where a different bone fragment lacerated a blood vessel.
Lung collapse or mechanical problem
Insufficient lung parenchymal function
Pulmonary vascular disease
Neurogenic respiratory distress
Support the patient with oxygen by nonrebreathing mask, or by intubation if appropriate, and evaluate coma and altered consciousness emergencies.
Metabolically induced respiratory distress
Patients at risk
People who have been exposed to smoke, toxic fumes, etc., may not initially be in respiratory distress, but the circumstances of the exposure can make it wise for them to be monitored for 24 to 72 hours. They need not be in an emergency department, but, depending on the specific incident, may be held at an observation facility, or discharged such that they are under responsible observation and can quickly be brought to an emergency facility. 
- ↑ The only intervention, assuming the patient is in a physically safe space, which will take priority is defibrillation for a witnessed cardiac arrest. Of course, if the patient is in a burning car or similar situation, extrication is an even higher priority.
- ↑ Tilt Head, Lift Chin, Check Breathing
- ↑ American Academy of Orthopaedic Surgeons, Emergency Care and Transportation of the Sick and Injured (4th ed.), ECAT, pp. 79-80
- ↑ An apparently unresponsive patient, who is also cold but but does not show injuries incompatible with life, justifies extensive resuscitative effort. A maxim of emergency medicine is "you're not dead until you're warm and dead". Children, especially, may go into an oxygen-conserving mammalian diving reflex when submerged in cold water; there have been neurologically complete recoveries after submersion of at least 45 minutes.
- ↑ Boozer, Harriet L & Melissa M Cheeseman (2004), Chapter 8, Compromised Airway, in Stone, CK and Humphries R, Current Emergency Diagnosis & Treatment (5th ed.), Lange Medical Books/McGraw-Hill, CEDT-08
- ↑ ECAT, p. 80
- ↑ ECAT, p. 88-90
- ↑ Editor, Trauma.org (November 24, 2006), Airway management of the Trauma Victim
- ↑ Udobi KF, Childs E, Touijer K. (2003 Jan 15), "Acute respiratory distress syndrome", Am Fam Physician 67(2): 315-22.
- ↑ Lillehei RC et al. (1964 October), "The Nature of Irreversible Shock: Experimental and Clinical Observations", Ann Surg. 160(4): 682–708.
- ↑ Patroniti, Nicolò et al. (2005), "Measurement of Pulmonary Edema in Patients With Acute Respiratory Distress Syndrome", Crit Care Med. 33(11): 2547-2554
- ↑ National Asthma Education and Prevention Program, Expert Panel Report III: Guidelines for the diagnosis and management of asthma, National Heart, Lung, and Blood Institute, 2007., NIH publication no. 08-4051
- ↑ Robert H. Demling, M.D. (May 16, 2008), "Smoke Inhalation Lung Injury: An Update", Eplasty: Open Access Journal of Plastic Surgery 8 (e27.)