Question 28

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