Investigations
1st investigations to order
chest x-ray
Test
Use chest x-ray as the first-line investigation in stable patients who can sit upright to definitively diagnose pneumothorax.
Order an erect postero-anterior (PA) x-ray in inspiration.
[Figure caption and citation for the preceding image starts]: Anterior-posterior chest x-ray demonstrating a right pneumothoraxFrom the collection of Dr Ryland P. Byrd [Citation ends].
Investigations to consider
chest ultrasound
Test
Chest ultrasound is increasingly used to detect pneumothorax, especially for patients who are immobilised following trauma, when an erect PA chest x-ray cannot be obtained. It requires specialist expertise.[54][55][56]
Result
absence of lung sliding (occurs when the visceral pleura does not slide against the parietal pleura[59][60]
the ‘A line’ sign (horizontal lines below the pleura caused by the presence of air)[59][60]
presence of ‘lung point’ (the point at which the two pleural layers rejoin one another from a pneumothorax)[59][60]
‘barcode sign’ (in M mode) where there is a pattern of parallel horizontal lines above and below the pleural line[61]
CT chest
Test
Order a CT chest if the diagnosis is uncertain on chest x-ray and the patient remains symptomatic, or in stable patients with significant chest trauma. If the patient is stable discuss this with a radiologist.[47]
Result
presence of a visible visceral pleural line
there may be atelectasis of lung or hyperexpansion of ipsilateral hemithorax; there may also be a partially adherent lung; CT guides the best place to insert a chest drain[62]
in secondary spontaneous pneumothorax there may be signs of underlying lung disease
arterial blood gas (ABG)
Test
Consider an ABG if oxygen saturations are ≤92% on room air. It may aid in ruling out other differential diagnoses but is not usually necessary.
Result
acute respiratory acidosis; escalate to a senior colleague if this is present
respiratory alkalosis is the most common finding[58]
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