Emergency Medicine

174 Tox icolog y

SPECIFIC POISONS

7 Otherwise observe all patients with clinical salicylate toxicity for a minimum

of 12 h until they demonstrate resolution of symptoms and a falling serum

salicylate level, before considering them medically stable.

8 Consult a clinical toxicologist for patients with salicylate levels >500 mg/L

(3.6 mmol/L), severe sy mptoms or obtunded.

(i) Consider haemodialysis for severe poisoning with a metabolic

acidosis or a salicylate level >700 mg/L (5.1 mmol/L).

Tricyclic antidepressants

DIAGNOSIS

1 Tricyclic antidepressant (TCA) overdose is associated with significant

mortality. Ingestion of ≥15–20 mg/kg is potentially fatal.

2 The onset of symptoms is usually rapid, and in large overdoses deterioration

occurs within 1–2 h. Significant toxicity is heralded by cardiotoxicity,

convulsions and coma.

3 Clinical features include:

(i) Anticholinergic: warm dry skin with absent sweating, dilated

pupils, urinary retention, sinus tachycardia, and delirium.

(ii) Central nervous system (CNS): seizures are usually associated

with an altered level of consciousness and rapid development of

coma, especially with a large overdose.

(iii) Cardiovascular: cardiac arrhythmias are common and occur as

a result of sodium-channel blockade. They are often associated

with hypotension.

4 Perform an ECG. Look for tachycardia, heart block, junctional rhythms

and ventricular tachycardia (VT) including polymorphic VT (torsades de

pointes).

(i) A QRS interval of >100 ms and right axis deviation indicate

cardiotoxicity and is predictive of ventricular arrhythmias.

5 Gain i.v. access and send blood for FBC, U&Es and a paracetamol level and

attach a cardiac monitor and pulse oximeter to the patient.

6 Perform an ABG to monitor for hypoxia and acidosis, both of which exacer-

bate cardiotoxicity.

MANAGEMENT

1 Give high-dose oxygen and commence a normal saline infusion.

2 Call an airway-skilled doctor to pass an endotracheal tube in patients with a

reduced conscious level, inadequate respiratory effort or convulsions, with

or without cardiac arrhythmias.

(i) The patient should be hyperventilated to a pH of 7.5, as

alkalaemia decreases the risk of cardiotoxicity.