acute dyspnoea / shortness of breath (SOB)

Introduction

A 2017-published international trial (Australia, NZ, Singapore, Malaysia,Hong Kong) of 3,044 people found: Patients with dyspnoea made up 5.2% of ED presentations, 11.4% of ward admissions, and 19.9% of intensive care unit (ICU) admissions. The most common diagnoses were lower respiratory tract infection (20.2%), heart failure (14.9%), chronic obstructive pulmonary disease (13.6%), and asthma (12.7%). Hospital ward admission was required for 64% of patients with 3.3% requiring ICU admission. In-hospital mortality was 6%.
In the ED a general approach to diagnosis starts with the common differentials.

Infection (eg pneumonia)
pulmonary embolism (PE)
Fluid maldistribution (eg Acute Decompensated LHF which is not, typically, fluid overload, as such)
Bronchospasm (eg exacerbation of asthma or chronic obstructive pulmonary disease (COPD))
anaphylaxis
pneumothorax

Oxygen (+ if the diagnosis is anaphylaxis: 10mcg/kg of IM adrenaline (adult dose 0.5mg))
Positive pressure (see noninvasive positive pressure ventilation (NPPV or NIPPV))
Pleural drainage
Antibiotics
Venodilators (eg GTN infusion or topical)
Steroids (Prednisolone po or hydrocortisone IV)
Beta-2 agonists (eg salbutamol)
Magnesium (usually as MgSO4 infusion)
Thrombolysis (in selected patients with intermediate or high risk PE, see thrombolysis in Mx of PE)
Anticoagulation (in all PE patients without a major contra-indication)
IM (Intra-Muscular) adrenaline is the specific treatment for anaphylaxis
Intubation and mechanical ventilation may be required in particular circumstances, for the critically ill.
Ketamine is the drug of choice for safer intubation of sick respiratory patients (see rapid sequence induction (RSI) for emergency intubation)

Acute Respiratory Distress Syndrome (ARDS)
pleural effusion
Malignancy
Aspiration pneumonitis
Transfusion associated acute lung injury
Transfusion associated circulatory overload (TACO)
inhaled foreign body
e-cigarette or vaping pulmonary injury
hypersensitivity pneumonitis / bird fancier's lung / farmer's lung - may present 4-6hrs after heavy exposure to the provoking antigen (eg. a protein in bird droppings if Bird Fancier's lung)
Chemical pneumonitis
Goodpasture's
anaemia
Sputum plugging
Thunderstorm “asthma” … this is really epidemic rye-grass allergy with bronchospasm (see thunderstorm asthma)
High altitude pulmonary oedema (HAPE)
Mitral regurgitation / valvular heart disease (e.g. rheumatic heart disease)
Neuromuscular disorders
Acidaemia (eg Kussmaul respiration in DKA)
Pericardial problems such as pericardial effusion, tamponade
Haemothorax
Pain
Psychogenic

CXR - will usually diagnose 3 of the 6 common causes
UEC - check the bicarbonate to rule out metabolic acidosis
FBE - lymphopenia, neutrophilia
D-dimer - interpreted in context; useful in selected patients with low pre-test probability of PE
VBG - sometimes helpful to monitor response to therapy
12 lead ECG - especially if tachycardic / bradycardic
CRP - greater than 60 is meaningful
CTPA or VQ scan are the two main options in patients with suspected PE
Bedside echo may be useful to look for pericardial problems or ventricular dysfunction