Sudden breathlessness, onset over seconds

This situation may be life-threatening; the severity of the underlying condition often creates helpful diagnostic information.

Pulmonary embolus
arising from DVT in leg, pelvic vein or right atrium
Suggested by: central chest pain also with abrupt shortness of breath, cyanosis, tachycardia, loud second sound in pulmonary area, associated DVT or risk factors of silent DVT. PO2 low, CO2 normal or low.

Confirmed by: V/Q scan ventilation/perfusion mismatch. Spiral CT scan: clot in artery, pulmonary angiogram shows filling defect (see above).
Management: OHCM pp96, 194, 802.

Pneumothorax
Suggested by: pain in centre or side of chest with abrupt breathlessness. Resonance to percussion over same side especially lung apex.

Confirmed by: expiration CXR showing loss of lung markings outside sharp line.
Management: OHCM pp194, 750, 798.

Anaphylaxis
Suggested by: dramatic onset over minutes, history of prior allergen exposure, acute bronchospasm with wheeze and dyspnoea, flushing, sweating and a feeling of dread, facial oedema, urticaria and warm but clammy extremities. Tachycardia and hypotension.

Confirmed by: clinical presentation and by controlled allergen exposure and examination. Response to adrenaline IM.
Management: OHCM p780, OHCS p237.

Inhalation foreign body
Suggested by: history of putting an object in mouth e.g. peanut. Sudden stridor, severe cough, low pitched, monophonic wheeze.

Confirmed by: relief in extremis by performing Heimlich manoeuvre etc. or if not in extremis, foreign body seen on CXR/CT or bronchoscopy.