Poisons Assessment ASSESSMENT Inspection of blood
Chocolate-coloured blood usually indicates methaemoglo- binaemia6 caused most commonly by abuse (inhalation or ingestion) of organic nitrites such as isobutyl nitrite or by drugs such as dapsone.
Pink plasma suggests haemolytic poisons (e.g. sodium chlorate).
Brown plasma suggests the presence of circulating myoglobin secondary to rhabdomyolysis.
Inspection of urine
Brown discoloration of the urine may be caused by the presence of haemoglobin (if there is intravascular hae- molysis), myoglobin secondary to rhabdomyolysis or metabolites of paracetamol.
Crystals may be prominent after ingestion of ethylene glycol or an overdose of primidone.
Radiology Routine radiology is of little diagnostic value. It can be used to confirm ingestion of metallic objects (e.g. coins, button batteries) or injection of globules of metallic mercury. Rarely, hydrocarbon solvents (e.g. carbon tetrachloride) may be seen as a slightly opaque layer floating on the top of the gastric contents with the patient upright, or outlining the small bowel. Some enteric- coated or sustained-release drug formulations may be seen on plain abdominal radiographs but, with the exception of iron salts, ordinary formulations are seldom seen. Radiography may have a limited role in confirming iron
overdose in children, but more widespread use in acute poisoning is restricted by the fact that many adult patients are women of child-bearing age. Ingested packets of illicit substances may be discernible on a plain radiograph, but CT or MRI is more reliably able to detect such objects. Radiology may be particularly helpful in confirming some of
the complications of poisoning, such as aspiration pneumonia, non-cardiogenic pulmonary oedema (salicylates), bronchiolitis obliterans (nitrogen oxides), ARDS, or pulmonary fibrosis (paraquat).
ECG
Routine ECG is of limited diagnostic value, though it should be recorded in those who have ingested potentially cardiotoxic drugs;19 continuous ECG monitoring may be appropriate in such patients. Sinus tachycardia with prolongation of the PR and QRS intervals in an unconscious patient should prompt consideration of tricyclic antidepressant overdose. With increasing cardiotox- icity, it may be impossible to detect P waves, and the pattern then resembles ventricular tachycardia. Overdose with cardiac glyco- sides or potassium salts also induces characteristic ECG changes. QeT interval prolongation is a recognized adverse effect of several drugs in overdose (e.g. quetiapine, terfenadine and
quinine) and predisposes to ventricular arrhythmias, notably torsade de pointes.20
A
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MEDICINE 40:2
These articles are reproduced by kind permission of Medicine Publishing.
www.medicinejournal.co.uk 52
44 Africa Health
2011 Published by Elsevier Ltd. July 2012
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