Phys · general-medicine
Undifferentiated Dyspnoea — A Systematic Diagnostic Approach
Also known as dyspnoea · breathlessness · shortness of breath · undifferentiated breathlessness · acute dyspnoea · chronic dyspnoea · respiratory distress · breathing difficulty · diagnostic approach to breathlessness · cardiac versus respiratory dyspnoea · BNP · NT-proBNP · Wells score · two-level PE rule · CURB-65 · Light's criteria · BLUE protocol · A-a gradient
Consultant-physician-depth guide to the diagnostic approach to the patient with breathlessness of unknown cause. Covers the acute-to-chronic time-course framework and its differentials, the focused history and examination discriminators, the first-tier investigations (blood gas, chest X-ray, ECG, NT-proBNP, troponin, D-dimer, FBC, U&E) and second-tier investigations (echo, PFTs, CTPA, V/Q, HRCT, cardiopulmonary exercise testing), the clinical decision rules (two-level Wells score for PE, CURB-65 for pneumonia, Light's criteria for pleural effusion), the BLUE protocol for bedside lung ultrasound, the natriuretic peptide algorithm for cardiac versus respiratory dyspnoea, and the DCE long-case and short-case approach. Structured for FRACP DWE and DCE preparation.
On this page
Study tools
Your progress
Saved on this device.
Practise this topic
Target exams
Red flags
- Acute dyspnoea with stridor is a threatened airway — call for senior airway help before any investigation; the time to intubation may be minutes
- Acute dyspnoea with a normal or near-normal chest X-ray, hypoxaemia and a raised A-a gradient is pulmonary embolism until proven otherwise — a normal X-ray does not exclude serious respiratory disease
- A falling oxygen saturation with a rising respiratory rate is physiological decompensation — oxygen saturation is a lagging marker, and by the time it falls the patient has exhausted reserve
- Type 2 respiratory failure (PaO2 below 8 kPa with CO2 above 6 kPa and a falling pH) in acute dyspnoea indicates ventilatory failure — the patient needs ventilatory support, not more oxygen alone
- The breathless patient who cannot speak in full sentences, who is using accessory muscles, or who is diaphoretic and agitated is in respiratory failure regardless of the oxygen saturation
- Anaphylaxis presents with acute dyspnoea plus airway or circulatory compromise and a rash — give intramuscular adrenaline 0.5 mg immediately, before any investigation
- A COPD patient who is breathless is not necessarily having an exacerbation — anchoring on COPD misses pneumothorax, pulmonary embolism, pneumonia and acute heart failure, all of which complicate COPD
Undifferentiated Dyspnoea — A Systematic Diagnostic Approach
The answer first
Dyspnoea of unknown cause spans five systems and kills by mismatch. The registrar's job is not to name a diagnosis in the first minute — it is to stabilise, anchor on the time course, and let the first-tier tests discriminate. Resist the pull of the premature diagnosis; the COPD patient who is "just exacerbating" is the one who dies of a missed pulmonary embolism.[1]
The reproducible sequence, applied to every breathless patient:[1]
- Stabilise if acute — ABCDE, oxygen to the hypoxaemic, treat the reversible killers (anaphylaxis, tension pneumothorax, airway obstruction) before chasing the label.
- Anchor on the time course — acute (minutes to hours), subacute (hours to days), chronic (weeks to months). No single axis generates a sharper differential.
- Take the focused history — onset, orthopnoea and PND, cough, sputum, haemoptysis, chest pain, leg swelling, travel, smoking, occupation, drugs.
- Examine systematically — respiratory rate and effort first, then the integrated respiratory and cardiovascular examination.
- Order first-tier tests together — blood gas, chest X-ray, 12-lead ECG, FBC, U and E, troponin, NT-proBNP, D-dimer if PE is plausible.
- Apply the discriminators — NT-proBNP for cardiac versus respiratory, Wells for PE, CURB-65 for pneumonia, Light's criteria for an effusion.
- Tier the second-line tests — echo, PFTs, CTPA or V/Q, HRCT, CPET — chosen by the working diagnosis, never as a blanket screen.[1]
The mantra that keeps the complex dyspnoeic patient safe: time course first, tests second, treat in parallel — never anchor. Oxygen and positioning buy time; they never replace a diagnosis.[1]
References11ShowHide
- [1]Maisel AS, Krishnaswamy P, Nowak RM, et al. Rapid measurement of B-type natriuretic peptide in the emergency diagnosis of heart failure N Engl J Med, 2002.PMID 12124404
- [2]Januzzi JL Jr, Camargo CA, Anwaruddin S, et al. The N-terminal Pro-BNP investigation of dyspnea in the emergency department (PRIDE) study Am J Cardiol, 2005.PMID 15820160
- [3]Wells PS, Anderson DR, Rodger M, et al. Derivation of a simple clinical model to categorize patients probability of pulmonary embolism: increasing the models utility with the SimpliRED D-dimer Thromb Haemost, 2000.PMID 10744147
- [4]van Belle A, Büller HR, Huisman MV, et al. Effectiveness of managing suspected pulmonary embolism using an algorithm combining clinical probability, D-dimer testing, and computed tomography JAMA, 2006.PMID 16403929
- [5]Lim WS, van der Eerden MM, Laing R, et al. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study Thorax, 2003.PMID 12728155
- [6]McDonagh TA, Metra M, Adamo M, et al. 2021 ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure Eur Heart J, 2021.PMID 34447992
- [7]Humbert M, Kovacs G, Hoeper MM, et al. 2022 ESC/ERS Guidelines for the diagnosis and treatment of pulmonary hypertension Eur Heart J, 2022.PMID 36017548
- [8]Hooper C, Lee YCG, Maskell N; BTS Pleural Guideline Group Investigation of a unilateral pleural effusion in adults: British Thoracic Society Pleural Disease Guideline 2010 Thorax, 2010.PMID 20696692
- [9]Lichtenstein DA, Mezière GA Relevance of lung ultrasound in the diagnosis of acute respiratory failure: the BLUE protocol Chest, 2008.PMID 18403664
- [10]Mueller C, McDonald K, de Boer RA, et al. Heart Failure Association of the European Society of Cardiology practical guidance on the use of natriuretic peptide concentrations Eur J Heart Fail, 2019.PMID 31222929
- [11]Bozkurt B, Coats AJS, Tsutsui H, et al. Universal definition and classification of heart failure: a report of the Heart Failure Society of America, Heart Failure Association of the European Society of Cardiology, Japanese Heart Failure Society and Writing Committee of the Universal Definition of Heart Failure: Endorsed by the Canadian Heart Failure Society, Heart Failure Association of India, Cardiac Society of Australia and New Zealand, and Chinese Heart Failure Association Eur J Heart Fail, 2021.PMID 33605000