Differentials
Non-toxic causes of wide complex tachycardia
SIGNS / SYMPTOMS
Absence of a history of a toxic ingestion should prompt consideration of non-toxic causes.
Successful cardioversion with treatment suggests a non-toxic cause; tachycardia due to an ingested toxin usually persists.
INVESTIGATIONS
On ECG, a widened QRS in conjunction with a rightward vector of the terminal 40 milliseconds of the frontal plane QRS suggests sodium channel toxicity subsequent to toxic ingestion. This is most easily identified as a widened (>1 mm) and enlarged (>1 mm) R wave in a VR and S wave in I and aVL. Non-toxic causes produce other patterns.
Administration of sodium bicarbonate to push the arterial pH to between 7.45 and 7.55 narrows the QRS complex in sodium-channel blocker toxicity. A lack of response excludes sodium-channel blocker toxicity.
Drug screen and drug levels are negative.
Non-toxic causes of status epilepticus
SIGNS / SYMPTOMS
A known diagnosis of epilepsy, with poor compliance to medication.
Other non-toxic causes are suggested by sudden-onset severe headache (intracranial haemorrhage), unilateral weakness (stroke), or fever (febrile seizure or central nervous system infection).
INVESTIGATIONS
Toxic and non-toxic seizures usually respond to benzodiazepines. Seizures also respond to sodium-channel anticonvulsants such as phenytoin.
Drug screen and drug levels are negative.
CT of the head and a lumbar puncture should be considered.
Non-toxic causes of anion gap metabolic acidosis
SIGNS / SYMPTOMS
Clinical distinction is difficult.
Absence of a history of a toxic ingestion or features specific to particular ingestions (e.g., vision or hearing loss, severe hypertension, recurrent seizures) should prompt consideration of non-toxic causes.
History of type 1 diabetes mellitus with a recent illness or sub-optimal insulin therapy should prompt consideration of diabetic ketoacidosis.
INVESTIGATIONS
Drug screen and drug levels are negative.
Hyperglycaemia with ketosis should prompt consideration of diabetic ketoacidosis.
Elevated serum urea and creatinine should prompt consideration of both toxic and non-toxic causes of acute kidney injury.
Non-toxic causes of altered mental status
SIGNS / SYMPTOMS
Non-toxic causes suggested by history of head trauma (intracranial bleeding), focal neurological signs (stroke), chest pain (myocardial infarction), fever with symptoms of infection (sepsis or any acute systemic infection), or abdominal pain with tenderness.
INVESTIGATIONS
No response to therapeutic trial of antidotes.
Drug screen and drug levels are negative.
Volume depletion in children
SIGNS / SYMPTOMS
Clinical evidence of excessive gastrointestinal losses, haemorrhage, diabetic ketoacidosis with polyuria, burns, heat stroke, fever, heavy exercise, anaphylaxis, sepsis, small-bowel obstruction, or ascites.
Signs of dehydration.
INVESTIGATIONS
Tachycardia is common.
BP may be slightly high (early stage) or low (late stage).
Drug screen and drug levels are negative.
Non-toxic causes of hypertension
SIGNS / SYMPTOMS
Absence of signs of central agitation or features of the antimuscarinic or sympathomimetic toxidromes suggests a non-toxic cause.
Absence of fever.
INVESTIGATIONS
Drug screen and drug levels are negative.
Non-toxic causes of fever
SIGNS / SYMPTOMS
Absence of features of sympathomimetic or antimuscarinic toxidromes, and absence of hyperreflexia, myoclonus, or rigidity, may suggest a non-toxic cause.
Clinical features of an underlying infection, inflammatory disorder, or malignancy.
INVESTIGATIONS
Drug screen and drug levels are negative.
Source of infection is found.
Non-toxic causes of bradycardia
SIGNS / SYMPTOMS
Absence of features of the cholinergic toxidrome, or of beta-blocker (peripheral shutdown with hypoglycaemia) or calcium-channel blocker toxicity (peripheral vasodilation with hyperglycaemia), may suggest a non-toxic cause.
Absence of a history of a toxic ingestion.
INVESTIGATIONS
Drug screen and drug levels are negative.
Bradycardia that responds to normal-dose atropine is less likely to be related to ingestion but may occur with some beta-blockers and calcium-channel blockers.
Inhalation injury
SIGNS / SYMPTOMS
History of exposure to a residential fire, workplace fire or explosion, or a chemical leak.
Similar symptoms to other patients at site of exposure.
Respiratory symptoms, including cough, dyspnoea, and tachypnoea.
Cyanosis, facial burns, hoarseness, dysphonia, or stridor.
INVESTIGATIONS
Hypoxaemia on pulse oximetry.
Increased carboxyhaemoglobin levels in carbon monoxide poisoning.
Air trapping, atelectasis, and airspace opacity on chest x-ray.
Snakebites
SIGNS / SYMPTOMS
History of snakebite, with fang marks, local redness, tenderness, pain, and swelling at wound site.
Weakness, dizziness, and perioral tingling or numbness are suggestive of envenomation.
There may also be bleeding and extensive swelling.
INVESTIGATIONS
No distinguishing tests.
Insect or spider bites and stings
SIGNS / SYMPTOMS
History of insect or spider bite or sting with pain, itching, or rash at the site of the bite.
Clinical features of anaphylaxis.
Pain, muscle cramps, diaphoresis, tremors, paraesthesias, nausea/vomiting, and headache suggest a black widow spider bite.
INVESTIGATIONS
No distinguishing tests.
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