Aspirin Overdose

Question 1

Define

Answer 1

excessive ingestion of aspirin causing toxicity

Effects are dose-related and potentially fatal:

 150mg/kg: mild toxicity
 250mg/kg: moderate
 >500mg/kg: severe toxicity
 Levels over 700mg/L are potentially fatal

Ingestion of 10–20g can cause moderate-to-severe toxicity in adults

Question 2

Causes

Answer 2

Aspirin is a weak acid with poor water solubility. It is present in many over-the counter preparations

Uncoupling of oxidative phosphorylation leads to anaerobic metabolism and the production of lactate and heat

It can be a result of deliberate self-harm, suicidal intent or by accident

10-20 g can cause moderate-severe toxicity in adults

Pathophysiology of Aspirin Overdose

1. Increases respiratory rate and depth by stimulating the respiratory centre
2. This hyperventilation –> respiratory alkalosis (in the early stage)
3. The body compensates by increasing urinary bicarbonate and K+ excretion
4. This leads to dehydration and hypokalaemia
5. Loss of bicarbonate, uncoupling of mitochondrial oxidative phosphorylation and the build up of lactic acid can lead to metabolic acidosis
6. In SEVERE cases, CNS depression and respiratory failure can occur

Question 3

Epidemiology

Answer 3

One of the MOST COMMON drug overdoses

Question 4

Symptoms

Answer 4

Unlike paracetamol, there are many early features

↘ Vomiting, dehydration, hyperventilation, tachypnoea

↘ Tinnitus, vertigo, deafness

↘ Sweating, flushed appearance

Later:

↘ Lethargy, confusion, drowsiness

Laura TanACUTE CARE AND TRAUMA 4

Unlike paracetamol, there are many early features

↘ Vomiting, dehydration, hyperventilation, tachypnoea

↘ Tinnitus, vertigo, deafness

↘ Sweating, flushed appearance

Later:

↘ Lethargy, confusion, drowsiness

More rarely:

↘ ↓GCS

↘ Seizures

↘ ↓BP and heart block

↘ Pulmonary oedema

↘ Hyperthermia

In severe overdoses → CNS depression and respiratory failure may occur

Question 5

Signs

Answer 5

fever, tachycardia, hyperventilation, epigastrictenderness

Present initially with respiratory alkalosis due to a direct stimulation of the central respiratory centres and then laterdevelop a metabolic acidosis

Hyper- or hypoglycaemia may occur.

Question 6

Investigation

Answer 6

Bloods

• Salicylate levels
• FBC
• U&Es - check for hypokalaemia
• LFTs - high AST/ALT
• Clotting screen - high PT
• Other drug levels (e.g. paracetamol)
• ABG - may show mixed metabolic acidosis and respiratory alkalosis

ECG

• Signs of hypokalaemia - flattened/inverted T waves, U waves, prolonged PR interval, ST depression