Respiratory failure occurs when the lungs cannot adequately oxygenate the blood or remove carbon dioxide. Boards emphasize the distinction between hypoxemic (type 1) and hypercapnic (type 2) failure, the causes of each, the blood gas findings, and the escalating levels of support.
Evidence-based · For exam prep, not medical advice
update Updated October 2026
Date of last content change
Built by surgery and anesthesiology residents·Written for USMLE Step 1
bolt The 60-second version
check_circleRespiratory failure is failure of oxygenation, ventilation, or both.
check_circleType 1 (hypoxemic) failure is a low PaO2 with a normal or low PaCO2.
check_circleType 2 (hypercapnic) failure adds an elevated PaCO2.
check_circleType 1 comes from gas-exchange problems; type 2 from failure to ventilate.
check_circleManagement ranges from oxygen to noninvasive and invasive ventilation.
Type 1 vs Type 2
Respiratory failure is divided by the arterial blood gas. Type 1 (hypoxemic) respiratory failure is defined by a low arterial oxygen (PaO2 below 60 mm Hg) with a normal or low carbon dioxide, reflecting a problem with gas exchange across the alveoli. Type 2 (hypercapnic) respiratory failure adds an elevated PaCO2 (above 50 mm Hg), reflecting inadequate ventilation to clear carbon dioxide. The two often overlap.
Causes
Type 1 failure results from conditions that impair oxygenation despite preserved effort — pneumonia, pulmonary edema, ARDS, and pulmonary embolism — typically through ventilation-perfusion mismatch or shunt. Type 2 failure results from inadequate ventilation — a "pump" problem — as in COPD exacerbations, drug overdose depressing the respiratory drive, neuromuscular disease, and severe asthma with fatigue. Recognizing which type points to the cause.
Diagnosis
The arterial blood gas is central: it establishes the PaO2 and PaCO2, classifies the type, and shows the acid-base status (acute hypercapnia causes respiratory acidosis). Pulse oximetry monitors oxygenation continuously, and the underlying cause is sought with imaging, history, and examination. Signs of increasing work of breathing and fatigue help judge how urgently support is needed.
Management
Treatment supports gas exchange while the underlying cause is treated. Supplemental oxygen corrects hypoxemia in type 1 failure (titrated cautiously in chronic CO2 retainers). Type 2 failure with respiratory acidosis often responds to noninvasive positive-pressure ventilation (such as BiPAP), which assists ventilation. When these fail or the patient cannot protect the airway, intubation and invasive mechanical ventilation are required.
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2 real questions on Respiratory Failure
Straight from the Progress Note question bank, each with a cited explanation. No account needed.
12
From our NCLEX bank
A nurse is caring for a client with a severe asthma exacerbation. The client was audibly wheezing, but the wheezing has now become faint and the chest is nearly silent while the respiratory rate rises. How should the nurse interpret this change?
Answer: D. A silent chest with a rising respiratory rate in severe asthma means air movement is so reduced that wheezing can no longer be produced, which signals impending respiratory failure (option D). Interpreting the change as improvement (A) is a dangerous error, because true improvement comes with better air movement and a normalizing effort. Offering only reassurance and rest (B) misses an emergency. Calling the findings expected airway relaxation (C) misreads an ominous sign. The loss of wheezing with worsening effort is the opposite of recovery. The nurse summons help immediately and prepares for aggressive treatment and possible ventilatory support.
A client with a severe asthma exacerbation has been treated with bronchodilators but is now tiring, with a falling oxygen saturation and a PaCO2 that has risen from low to normal. How should the nurse interpret this change?
Answer: C. In a severe asthma exacerbation the PaCO2 is usually low from hyperventilation, so a PaCO2 rising to normal along with fatigue and falling oxygen saturation signals that the client can no longer sustain the work of breathing and is heading toward respiratory failure, warranting urgent escalation (option C). Interpreting the normalizing PaCO2 as improvement (A) is a dangerous error. Calling it an expected response to bronchodilators (B) misreads an ominous sign. Offering only reassurance and routine observation (D) misses an emergency. Recognizing the deceptively normal PaCO2 with fatigue as impending failure is the key judgment. The nurse summons help and prepares for possible ventilatory support.
What is the difference between type 1 and type 2 respiratory failure?expand_more
Type 1 (hypoxemic) respiratory failure is a low arterial oxygen (PaO2 below 60 mm Hg) with normal or low carbon dioxide, from a gas-exchange problem. Type 2 (hypercapnic) failure adds an elevated PaCO2 (above 50 mm Hg), reflecting inadequate ventilation. They can coexist.
What causes hypoxemic respiratory failure?expand_more
Type 1 hypoxemic respiratory failure is caused by conditions that impair oxygen exchange, such as pneumonia, pulmonary edema, ARDS, and pulmonary embolism, usually through ventilation-perfusion mismatch or shunt.
What causes hypercapnic respiratory failure?expand_more
Type 2 hypercapnic respiratory failure results from inadequate ventilation — a pump failure — as in COPD exacerbations, opioid or sedative overdose depressing respiratory drive, neuromuscular disease, and severe fatigue in asthma.
How is respiratory failure treated?expand_more
Management supports gas exchange while treating the cause: supplemental oxygen for hypoxemia, noninvasive positive-pressure ventilation (such as BiPAP) for hypercapnic failure with respiratory acidosis, and intubation with invasive mechanical ventilation when noninvasive support fails or the airway is unprotected.
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