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
Airway
  • Foreign body
  • Angioedema and anaphylaxis
  • Obstructive airway infections, eg. retropharyngeal abscess
  • Airway trauma
  • Endotracheal tube malposition
Breathing
  • 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
Circulation
  • Cardiogenic pulmonary oedema, due to...
    • Acute coronary syndrome
    • Heart failure, cardiomyopathy
    • Arrhythmia
    • Valve failure
    • Cardiac tamponade
Neurology
  • 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
History
  • 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
Examination
  • 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
Bloods
  • 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)
Imaging
  • 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

 

 

 

References