Investigations
1st investigations to order
pulse oximetry
Test
Monitor oxygen saturation if there are any features of central nervous system (CNS) depression, as respiratory and CNS depression may coexist.[24]
Result
normal in mild overdose
arterial/venous blood gas
Test
Consider in any patients with:[24]
Reduced oxygen saturation noted on pulse oximetry
Reduced level of consciousness
Metabolic disturbance.
Result
hypoxia and/or hypercapnia in patients with reduced consciousness
possible metabolic acidosis in patients who have taken a significant overdose
FBC
Test
Perform in all patients with suspected overdose as part of a basic screen.
Result
normal
urea and electrolytes
Test
Perform in all patients with suspected overdose as part of a basic screen.
Result
following a significant overdose and reduced conscious level, patients may develop acute kidney injury with or without rhabdomyolysis
liver function tests
Test
Perform in all patients with suspected overdose as part of a basic screen.
Patients with severe liver disease are at risk of toxicity from lower doses.[24]
Poor liver function may be a precipitating factor for the benzodiazepine overdose as most benzodiazepines are metabolised by cytochrome p450 enzymes.
Result
often normal although abnormalities may occur
consider underlying liver disease or co-ingestion of another agent (e.g., paracetamol)
ECG
Test
Perform in all patients with suspected overdose as part of a basic screen to exclude other causes of symptoms and to assess any cardiac effects of the overdose.
Consider repeating in symptomatic patients, those with an abnormal result, or in those in which the recommended observation period is not complete.[24]
Result
abnormalities may include transient first degree and second degree heart block and QT prolongation[24]
creatine kinase
Test
Check creatine kinase where there is concern about a long lie or convulsions with the potential for rhabdomyolysis.[24]
Result
elevated creatine kinase would indicate rhabdomyolysis
plasma paracetamol concentration
Test
Consider the possibility of a mixed overdose involving paracetamol, particularly if you suspect an intentional overdose:
Measure plasma paracetamol concentration in a patient who is unconscious or is unable to give a reliable history.[28]
See Paracetamol overdose in adults for more information.
Result
indicates paracetamol ingestion
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