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Respiratory failure is the acute or chronic inability of the respiratory system to maintain gas exchange (PaO2 < 60 mm Hg, PaCO2 > 50 mm Hg). Causes can be extrapulmonary (e.g., CNS depression due to narcotic overdose) as well as pulmonary (e.g., acute exacerbation of COPD). Respiratory failure can be classified as hypoxemic (type 1) or hypercapnic (type 2). Clinical features of hypoxemia include respiratory distress, cyanosis, tachycardia, and altered mental status. Clinical features of hypercapnia include hypoventilation, headache, warm extremities, and asterixis. Diagnostics include arterial blood gas analysis and possibly chest imaging to detect the underlying disease. Treatment includes supportive measures (oxygen delivery and/or ventilator support) and treatment of the underlying condition. Complications may arise due to prolonged hypoxemia and can affect various organs (e.g., renal/heart failure, brain damage).
- Respiratory failure: the acute or chronic inability of the respiratory system to maintain adequate gas exchange 
- Respiratory arrest: the complete cessation of breathing in patients with a pulse 
- Respiratory distress: A clinical syndrome associated with breathing disorders (See “ .”)
By gas exchange abnormality
|Types of respiratory failure |
|Type 1 (hypoxemic respiratory failure)||Type 2 (hypercapnic respiratory failure)|
|PaO2|| || |
|PaCO2|| || |
By duration 
- Acute respiratory failure: develops over minutes to hours as a result of an acute illness or insult
- Chronic respiratory failure: longstanding respiratory failure resulting from chronic illness (e.g., COPD, ILD, obesity hypoventilation syndrome)
In patients with hypercapnia, a normal pH suggests chronic CO2 retention while a low pH raises concern for acute or acute-on-chronic CO2 retention, which requires immediate intervention (see also “ .”)
Causes of hypoxemia 
- Impaired alveolar diffusion (e.g., due to pulmonary edema, severe pneumonia, pulmonary hemorrhage , idiopathic pulmonary fibrosis)
- Right-to-left shunt
- V/Q mismatch (e.g., due to severe pneumonia, pulmonary edema, pulmonary embolism, atelectasis)
- Decreased FiO2 (e.g., due to asphyxiant gas exposure, high altitude illness)
- Hypoventilation (see “Causes of hypercapnia”) 
Causes of hypercapnia 
- Airway obstruction and/or increased physiologic dead space due to:
- CNS depression (e.g., due to opioid intoxication, benzodiazepine intoxication, barbiturate intoxication, TBI, cerebral herniation, stroke, inhalant-related disorders)
- Respiratory muscle weakness (e.g., due to myasthenia gravis, Guillain-Barré syndrome, myopathies, ALS, high cervical spinal cord injury, poliomyelitis)
- Decreased chest wall compliance (e.g., due to rib fractures, tetanus, seizures, fibrothorax; , , )
- Electrolyte disturbances (e.g., anorexia nervosa)
By affected system
Respiratory: clinical features of respiratory distress
- Increased respiratory drive: tachypnea, hyperventilation
- Increased work of breathing (increased respiratory effort)
- Other agitation, cyanosis :
- Inability to lie flat
- CNS: altered
By underlying process
- Clinical features of hypoxemia
- Clinical features of hypercapnia
Clinical features of the underlying condition
- Fever, e.g., due to sepsis, pneumonia
- Cough, e.g., due to pneumonia, COPD
- Chest pain, e.g., due to pneumonia, pulmonary embolism
- Signs of general muscle weakness, e.g., due to myasthenia gravis, Guillain-Barré syndrome, myopathies, ALS
- Pain on inspiration, e.g., due to rib fracture
- CNS depression, e.g., due to opioid use
Recognize signs of imminent or ongoing respiratory arrest (e.g., gasping, inspiratory stridor, decreased respiratory rate, cyanosis, absent chest rise, or acute oxygen desaturation) and treat it immediately if present.
- Use including IV access, pulse oximetry, and cardiac monitoring.
- Provide immediate respiratory support tailored to the underlying cause and severity of respiratory failure.
- Ascertain early if feasible.
- Identify and treat .
- Perform focused clinical evaluation.
- Obtain initial diagnostics: e.g., ABG, routine laboratory studies, ECG, CXR, POCUS
- Consider advanced diagnostic testing based on initial findings.
- : Secure the airway if are present.
- : indicated immediately for patients in respiratory arrest
Treatment of rapidly reversible causes of respiratory failure
Respiratory failure and respiratory arrest are . ABG analysis, rapid laboratory studies, and bedside imaging can help identify the type of respiratory failure and guide treatment of the underlying cause.
Respiratory failure and arrest require immediate management, i.e., prior to diagnostic confirmation.
Initial investigations 
- ABG: for diagnostic confirmation
- CBC: to assess for anemia
- BMP: to assess for metabolic and electrolyte derangements
- Consider the following based on clinical suspicion:
Bedside imaging 
- CXR: to assess for chest wall, pleural, and/or lung lesions (e.g., trauma, ARDS, pneumonia, pneumothorax, atelectasis, pleural effusion)
- POCUS: to assess lung, pleura, heart, pericardium, and deep veins
POCUS may help to quickly identify pneumothorax, pulmonary edema, pleural effusions, heart failure, cardiac tamponade, or the presence of DVT and/or signs of acute right heart strain suggesting pulmonary embolism.
Advanced diagnostic testing 
- CT chest: for detailed pulmonary evaluation (e.g., trauma, ARDS, tumor, pleural effusion, pneumonia)
- CTA chest: for suspected pulmonary embolism
- Echocardiography: for suspected heart failure, cardiac tamponade, or signs of right heart strain suggesting pulmonary embolism or pulmonary hypertension
- CT head: for suspected head trauma or stroke
- CO-oximetry: to assess for or
Treatment of the underlying cause of respiratory failure
The following is a nonexhaustive list of common causes of respiratory failure. See also “ .”
|Common causes of respiratory failure and their management|
|Suggestive features||Cause-specific management|
| || |
|CNS causes of respiratory failure|| |
Monitoring and disposition 
- Pulmonary: e.g., irreversible lung scarring after pulmonary embolism or pneumonia, ventilator dependence
- Cardiac: : e.g., arrhythmias, heart failure, cardiac arrest
- Neurological: : e.g., hypoxic brain injury, irreversible brain damage, brain death
- Renal: e.g., acute renal failure
- Gastrointestinal: e.g., stress ulcer, ileus
- Nutritional: e.g., hypoglycemia, electrolyte disturbances
- Other: hypoxic damage to other organs
We list the most important complications. The selection is not exhaustive.