Causes of respiratory failure

Several past paper SAQs demand the candidate either generate a list of differentials (such as the diferentials for a diffuse pulmonary infiltrate) or define a sensible approach to the assessment of acute respiratory failure.

  • Question 4  from the second paper of 2012 (a tracheostomy patient short of breath)
  • Question 15.2 from the second paper of 2012 (a patient undergoing radiotherapy)
  • Question 28 from the first  paper of 2010 (a post-op trauma patient)
  • Question 28 from the second paper of 2005 (COPD)
  • Question 2b from the first  paper of 2004 (PE)

This is a very artificial list of causes and investigations. It has been derived from the excellent UpToDate topic, "Evaluation of the adult with dyspnea in the emergency department".

Causes of Respiratory Failure
  • Foreign body
  • Angioedema and anaphylaxis
  • Obstructive airway infections, eg. retropharyngeal abscess
  • Airway trauma
  • Endotracheal tube malposition
  • Pulmonary embolism
  • Bronchospasm: COPD or asthma
  • Pneumothorax
  • Infection: pneumonia, pneumonitis, etc etc
  • ARDS from a pulmonary or non-pulmonary source
  • Pleural effusion for whatever reason
  • Post-operative atelectasis
  • Cardiogenic pulmonary oedema, due to...
    • Acute coronary syndrome
    • Heart failure, cardiomyopathy
    • Arrhythmia
    • Valve failure
    • Cardiac tamponade
  • Neurogenic pulmonary oedema
  • Neuromuscular disease, with respiratory muscle weakness
  • Respiratory center injury, eg. stroke
  • Anxiety, hyperventilation
Endocrine and metabolic
  • Metabolic acidosis
  • Poisoning,  respiratory suppressants eg. opiates or respiratory stimulants eg. salicylates
  • Massive obesity
  • Hyperthyroidism
  • Neuromuscular disease, with respiratory muscle weakness
  • Respiratory center injury, eg. stroke
Haematological and oncological
  • Failure of oxygen-carrying capacity or oxygen delivery:
    • Anaemia
    • Dyshaemoglobinaemia
    • Carbon monoxide or cyanide toxicity
  • Malignancy, local (eg. bronchial carcinoma) or infiltrative (eg. lymphoma or lymphangitis carcinomatosis)
Infectious and immunological
  • Sepsis
  • Autoimmune SIRS or vasculitis
  • Graft vs host phenomena, eg. TRALI or engraftment syndrome


In the post-op trauma patient, the list would consist of the following:

  • Vascular/embolic causes:
    • Fat embolism
    • Pulmonary thromboembolism
    • Pulmonary oedema due to MI
  • Infectious causes:
    • Aspiration pneumonia
  • Drug-associated causes:
    • Opiate-associated respiratory depression
  • Iatrogenic causes:
    • ETT maplosition
    • TRALI
    • Atelectasis
    • Resuscitation-associated fluid overload
  • Autoimmune causes
    • Anaphylaxis
  • Traumatic causes
    • Pneumothorax
    • Cardiac tamponade
    • Pulmonary contusions
Investigations for Acute Respiratory Failure
  • General historical features
  • Past history
  • Chronology of the episode
  • Prior intubation
  • Severity of distress
  • Association of chest pain
  • History of trauma
  • Fevers, chills, rigors, night sweats
  • Cough, sputum, haemoptysis
  • Recent travel
  • Tobacco and drugs
  • Basic vital signs, including temperature and oximetry
  • Red flags:
    • Obtubdation
    • Fatigue
    • Cyanosis
  • Features of severe respiratory distress:
    • Retractions and the use of accessory muscles
    • Brief, fragmented speech
    • Inability to lie supine
    • Profound diaphoresis; dusky skin
    • Agitation or other altered mental status
  • Palpation, percussion, auscultation of the chest
  • Full blood count (anaemia, WCC)
  • Inflammatory markers (infection, malignancy)
  • Urea creatinine and electrolytes (organ system function and acid-base balance)
  • ABG (gas exchange and acid-base balance)
  • Chest Xray
  • ECG
  • Trans-thoracic echo (TTE)
  • CT of the chest, +/- pulmonary angiogram
Potentially relevant investigations
  • Spirometry
  • Cardiac biomarkers
  • Procalcitonin
  • Urinary pneumococcal and legionella antigens
  • Sputum culture
  • PJP PCR on sputum
  • Aspergillus galactomannan