A 65 year old woman with chronic airways disease presents with acute respiratory failure.

Outline  how  you  would  establish  the  precipitating cause  of  her acute  respiratory failure.

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College Answer

History: consider

•    Duration of respiratory failure – is it acute deterioration on a normal functional background or acute on chronic?;

•    setting (in community or hospital); any trauma/surgery/anaesthesia/procedure related;

•    respiratory depressant drug use;

•    fever/sweats/cough/sputum production;

•    history of others developing respiratory infection or epidemics;

•    recent travel especially overseas;

•    history of DVT/PE, malignancy, cigarette smoking,

•    recent chest pain or symptoms of heart failure;

•    medication use related to potential anaphylaxis or upper airway oedema;

•    is there a septic or SIRS process generating a metabolic acidosis that this patient’s respiratory system cannot deal with?

Examination: consider

•    Level of consciousness

•    presence of stridor or wheeze

•    cyanosis indicative of oxygenation failure

•    barrel chested / pursed lips / nasal flaring indicating hyperinflation

•    tracheal deviation indicating severe collapse or PTX;

•    subcutaneous emphysema;

•    flap indicative of hypercapnia;

•    ?new heart murmur or other signs indicative of heart failure;

•    signs of non-respiratory sepsis (eg abdomen) or SIRS generating a severe metabolic acidosis;

•    focal limb oedema. Investigation: consider

•    ABG – assess oxygenation/ventilation/acid-base status (metabolic and respiratory)

•    Spirometry – obstructive or restrictive airflow pattern

•    Hb – is there polycythaemia due to chronic severe disease or severe anaemia contributing decreased O2 delivery?

•    ECG – is there RHF or myocardial ischaemia?

•    CXR – collapse / PTX / pneumonia / heart size / pulmonary oedema / hyperinflation /effusion / trauma / malignancy / airway compression.

•    Sophisticated investigations like thoracic CT are not necessarily appropriate in the acute setting unless suspecting a PE.

•    Possible use of V/Q scanning.

Discussion

This question is painfully broad.  It requires the candidate to think carefully about the diagnostic pathway in respiratory failure. A structured response is always better. This one 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
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
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
  • Hy
  • 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

 

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