Investigations
1st investigations to order
pulse oximetry
Test
Helpful for initial assessment.
Pulse oximetry under-detects hypoxaemia in the setting of carboxyhaemoglobin, and will appear normal even in patients with significantly elevated carboxyhaemoglobin (CO-Hb) levels.
Result
hypoxaemia
arterial blood gas
Test
Severe acidosis may suggest hypoperfusion from shock, carbon monoxide poisoning, or cyanide toxicity.
Result
may show severe metabolic acidosis
carboxyhaemoglobin (CO-Hb) level
Test
Normal levels are around 1% to 3% and in smokers up to 10%. Carbon monoxide (CO)-oximetry should be used to measure CO-Hb levels.
Arterial sampling is not necessary as there is a high correlation between venous and arterial samples.
Result
CO-Hb level >15% in carbon monoxide poisoning
chest x-ray
Test
Air trapping and atelectasis suggest airway injury, obstruction, and collapse.
Pulmonary oedema may suggest acute respiratory distress syndrome or cardiogenic oedema.
Result
air trapping; atelectasis; airspace opacity (oedema)
ECG
Test
Increased cardiac demand, inflammation, and systemic and cellular hypoxia associated with burn and inhalation injury all predispose to cardiac ischaemia.
Result
arrhythmias, ischaemia
cardiac telemetry monitoring
Test
Increased cardiac demand, inflammation, and systemic and cellular hypoxia all predispose to cardiac ischaemia or arrhythmias.
Result
arrhythmias
urine toxicology screen
Test
There is a high incidence of intoxication among victims of residential fires in particular.[24]
Result
evidence of illicit drug use
serum ethanol level
Test
There is a high incidence of intoxication among victims of residential fires in particular.[24]
Result
elevated blood alcohol level in intoxicated patients
Investigations to consider
pulmonary function tests (PFT)
Test
If available, PFT may allow characterisation and serial measurement of airflow obstruction.
Result
Decreased FEV1 or forced vital capacity; flow-volume loop suggesting obstruction
laryngoscopy and bronchoscopy
Test
Many practitioners advocate these procedures to assess airway oedema, although clear evidence of benefit is lacking.[19]
Result
Airway oedema, burn, or ulceration; debris in airways
serum lactate
Test
While often interpreted as evidence of cyanide toxicity, this test is non-specific and probably represents hypoperfusion and carbon monoxide poisoning more commonly.[20]
Result
Elevation of lactate level
Emerging tests
cyanide level
Test
A rapid point-of-care test is not commercially available, but a simple optical analyser has been developed which accurately detects cyanide levels of imminent concern in around 2 minutes, as well as a paper microfluidic device that successfully measured cyanide ions in the blood samples of 20 fire survivors.[20][22][23]
Result
level greater than 11.62 micromol/L (0.5 mg/L)
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