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:
- Drug-associated causes:
- Opiate-associated respiratory depression
- Iatrogenic causes:
- ETT maplosition
- TRALI
- Atelectasis
- Resuscitation-associated fluid overload
- Autoimmune causes
- 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
|