*Airway obstruction: Obstruction may occur in the upper and lower airway. *Upper airway: Obstruction of the upper airway is common in infants less than 3 months old because they are nose breathers. Nasal blockage may easily lead to upper airway obstruction in infants. For other ages, upper airway obstruction may occur from a foreign body or edema of the pharynx, larynx, or trachea. In cases of decreased or total loss of consciousness, the tongue can lose muscle tone and obstruct the upper airway. Other potential causes of obstruction include tumors of the upper<unk>  tract (oral cavity, pharynx, larynx), bodily fluids (blood, mucus, vomit), and trauma to the upper airway. The most common type of tumor of upper<unk>  tract is squamous cell carcinoma, with the greatest risk factors for this condition being alcohol and tobacco use, with HPV (genotype 16) being another important risk factor. An epidemiological study of over 5 million cases of head and neck trauma in the United States resulting in visits to the emergency department found that the majority occur due to falls or blunt force, with foreign body injuries being more common in the pediatric population. *Lower airway: may occur from bronchospasm, drowning, or airspace filling disorders (e.g. pneumonia, pulmonary edema, pulmonary hemorrhage). Obstructive conditions of the lower airway, including severe asthma or COPD episodes, can also lead to<unk> . During these episodes, known as exacerbations, airway resistance is increased due to inflammatory changes in the lungs. This leads to increased work of breathing and decreased oxygen delivery to tissue. In asthma, this involves bronchiolar constriction whereas in COPD this involves small airway collapse during expiration and subsequent air-trapping. One of the ways the body attempts to compensate for these increased<unk>  demands is by increasing<unk>  rate, which in turn worsens<unk>  muscle fatigue of the diaphragm and can eventually lead to<unk>  and death without timely medical intervention. *Decreased<unk>  effort: Central nervous system impairment leads to decreased<unk>  effort. The<unk>  center of the brain is located in the pons and medulla and is primarily driven by elevated carbon dioxide levels in the blood (hypercapnia) with decreased oxygen levels (hypoxemia) serving as a less potent stimulus. Central nervous system disorders, such as stroke and tumors, may cause hypoventilation. Drugs may decrease<unk>  effort as well, such as opioids, sedative-hypnotics, and alcohol. These lower<unk>  drive by blunting the response of the<unk>  center of the brain to hypercapnia. Metabolic disorders could also decrease<unk>  effort. Hypoglycemia and hypotension depress the central nervous system and compromise the<unk>  system.<unk>  muscle weakness: Neuromuscular disorders may lead to<unk>  muscle weakness, such as spinal cord injury, neuromuscular diseases, and neuromuscular blocking drugs.<unk>  muscle fatigue can also lead to<unk>  muscle weakness if patients breathe over 70% of their maximum voluntary ventilation. Breathing over an extended period of time near maximum capacity can cause metabolic acidosis or hypoxemia, ultimately leading to<unk>  muscle weakness.
Respiratory arrest
Cardiac arrest
Sleep paralysis
Syncope 
Expiratory apnea
Spinal shock
Permissive hypotension
Inert gas asphyxiation