Respiratory Failure


  • Respiratory Failure: failure of respiratory system to maintain adequate gas exchange
    • Inability to maintain normal hemoglobin saturation (hypoxemia) and/or tissue oxygenation (hypoxia)
    • Inability to maintain normal arterial pCO2 (hypercapnia)
    • Inability to maintain normal pH (acidemia) with or without a concomitant metabolic acidosis

Classification Schemes for Respiratory Failure

Classification Based on the Predominant Gas Exchange Abnormality and Time of Onset


Type 1-Hypoxemic Respiratory Failure

  • Etiology: associated with any type of lung disease which results in alveolar filling and/or atelectasis (collapse)
  • Subtypes
    • Acute Hypoxemic Respiratory Failure (see Hypoxemia, [[Hypoxemia]])
    • Chronic Hypoxemic Respiratory Failure (see Hypoxemia, [[Hypoxemia]])

Type II-Ventilatory/Hypercapnic Respiratory Failure (aka Hypoxemic-Hypercapnic Respiratory Failure)

  • Etiology: associated with only specific types of lung disease
  • Subtypes: the accompanying pH depends on the level of serum bicarbonate (which is dependent on the duration of the hypercapnia)
    • Acute Hypercapnic Respiratory Failure (see Acute Hypoventilation, [[Acute Hypoventilation]]): pH may be more decreased (due to inadequate time for renal reabsorption of bicarbonate)
    • Chronic Hypercapnic Respiratory Failure (see Chronic Hypoventilation, [[Chronic Hypoventilation]]): pH generally normal or only slightly decreased (due to prolonged duration, allowing for renal reabsorption of bicarbonate)

Potential Clinical Exceptions to This Classification Scheme

  • Exception: patient with prolonged, severe hypoxemia (initially classified as type I-acute hypoxemic respiratory failure), with the inability to maintain the required work of breathing, subsequently resulting in acute respiratory muscle fatigue with onset of acute hypercapnia (now classified as type II-hypercapnic/ventilatory failure) -> note that the classification of the patient’s respiratory failure changed during their clinical course
    • Example: 50 y/o WM with history of COPD and AIDS, presenting with PCP and severe acute hypoxemia
  • Exception: patient with increased work of breathing/increased minute ventilation (due to severe metabolic acidosis) without significant hypoxemia or hypercapnia -> note that such a patient may manifest imminent “respiratory failure”, although not technically fulfilling the criteria for either type I or type II respiratory failure
    • Example: 30 y/o WM with severe diabetic ketoacidosis (pH 6.9/pCO2 20/pO2 65/bicarb 3 + RR 36)

Classification Based on Anatomic Site of Dysfunction

  • Obstructive Lung Disease
    • Example: Airway Tumors
    • Example: Asthma
    • Example: Chronic Obstructive Pulmonary Disease (COPD)
    • Example: Mucous Plugging of Airway
  • Alveolar Disease
    • Example: Acute Lung Injury (ALI)/Adult Respiratory Distress Syndrome (ARDS)
    • Example: Diffuse Alveolar Hemorrhage (DAH)
    • Example: Pneumonia
    • Example: Pulmonary Alveolar Proteinosis (PAP)
    • Example: Pulmonary Edema
  • Interstitial Lung Disease (ILD)
    • Example: Acute Lung Injury (ALI)/Adult Respiratory Distress Syndrome (ARDS)
    • Example: Hypersensitivity Pneumonitis (HP)
    • Example: Idiopathic Pulmonary Fibrosis (IPF)
    • Example: Viral Pneumonia
  • Cardiac/Pulmonary Vascular Disease
    • Example: Congestive Heart Failure (CHF)
    • Example: Idiopathic Pulmonary Arterial Hypertension (IPAH)
    • Example: Intracardiac Shunt
    • Example: Intrapulmonary Shunt
    • Example: Pulmonary Edema
    • Example: Pulmonary Embolism
  • Pleural Disease
    • Example: Fibrothorax
    • Example: Pleural Effusion
    • Example: Pneumothorax
  • Neuromuscular Disease
    • Example: Guillain-Barre Syndrome (GBS)
    • Example: Myastenia Gravis
    • Example: Myopathy

Classification Based on Pathophysiologic Mechanism

  • Decreased Inspired Oxygen Pressure
    • ABG (typical)
      • pCO2: Normal-Decreased
      • pO2: Decreased
  • Acute Hypoventilation
    • ABG (typical)
      • pH: Decreased (acidemia)
      • pCO2: Increased
      • pO2: Decreased
      • Serum Bicarbonate: Normal
  • Chronic Hypoventilation
    • ABG (typical)
      • pH: Near Normal
      • pCO2: Increased
      • pO2: Decreased
      • Serum Bicarbonate: Increased
  • V/Q Mismatch
    • ABG (typical)
      • pCO2: Normal-Decreased
      • pO2: Decreased
  • Shunt
    • ABG (typical)
      • pCO2: Normal-Decreased
      • pO2: Decreased
  • Diffusion Impairment
    • ABG (typical)
      • pCO2: Normal-Decreased
      • pO2: Decreased


  • Arterial Blood Gas (ABG): required
  • Pulse Oximetry: information provided is limited to oxygen saturation (but importantly neglects the pH and pCO2, which are crucial to allow the detection of hypercapnia)
  • End-Tidal CO2: may be useful to detect hypercapnia
  • Transcutaneous CO2: may be used
  • CXR/Chest CT: useful to identify underlying etiology


Oxygen (see Oxygen, [[Oxygen]])

Nasal Cannula (NC)

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High-Flow Nasal Cannula (HFNC)

  • Rationale: high-flow nasal cannula appears to decrease dead space [MEDLINE]
  • Contraindications
    • Hypercapnic Respiratory Failure
    • Mid-Maxillary Facial Trauma
    • Suspected Pneumothorax
  • French FLORALI Study Comparing High-Flow Nasal Cannula Oxygen with Standard Oxygen and Non-Invasive Ventilation in Hypoxemic, Non-Hypercapnic Respiratory Failure (NEJM, 2015) [MEDLINE]
    • No Difference in Intubation Rates
    • High-Flow Oxygen Group: improved 90-day mortality
    • High-Flow Oxygen Group: improved ventilator-free days
    • Criticisms of Study
      • Non-invasive ventilation group was unconventionally ventilated with 9 ml/kg PBW, possibly increasing lung injury int his group


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Non-Rebreather Mask

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Mechanical Ventilation (see General Ventilator Management, [[General Ventilator Management]])

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Noninvasive Positive-Pressure Ventilation (NIPPV)

Mechanical Ventilation


  • The continuous inhalation of oxygen in cases of pneumonia otherwise fatal, and in other diseases. Boston Med J 1890;123:481-5
  • High-flow oxygen administration by nasal cannula for adult and perinatal patients. Respir Care 2013;58:98-122
  • Nasal high-flow versus Venturi mask oxygen therapy after extubation: effects on oxygenation, comfort, and clinical outcome. Am J Respir Crit Care Med 2014;190:282-8
  • Transnasal humidified rapid-insufflation ventilatory exchange (THRIVE): a physiological method of increasing apnoea time in patients with difficult airways. Anaesthesia 2015;70:323-9 [MEDLINE]
  • FLORALI Study. High-flow oxygen through nasal cannula in acute hypoxemic respiratory failure. N Engl J Med 2015. DOI: 10.1056/NEJMoa1503326 [MEDLINE]
  • Saving lives with high-flow nasal oxygen. N Engl J Med. 2015 Jun 4;372(23):2225-6. doi: 10.1056/NEJMe1504852. Epub 2015 May 17 [MEDLINE]
  • High-flow nasal cannula oxygen therapy in adults. J Intensive Care. 2015 Mar 31;3(1):15. doi: 10.1186/s40560-015-0084-5. eCollection 2015 [MEDLINE]