Last Updated on February 3, 2019 by FRCEM Intermediate

Overview

• aspirin
• mechanisms of toxicity: acid-base disturbance, uncoupling of oxidative phosphorylation, disordered glucose metabolism
• Toxic dosage: ingestion of 125 mg/kg or more (or unknown) salicylate
• Large overdoses may ‘clump together’ In the stomach, causing delayed absorption

Clinical Features

• Early features: Tinnitus, nausea, hyperventilation, respiratory alkalosis
• Later features: Vomiting, sweating, metabolic acidosis, dehydration, hypoglycemia, hyperglycemia
• Very severe: Confusion, coma, pulmonary oedema, acute kidney injury , complex electrolyte disturbances

Acid-base disturbance: Respiratory alkalosis, elevated anion gap metabolic acidosis. If acidosis is present this is a late sign and indicates imminent demise without intervention

Dose-Related risk assessment 

Levels alone should not guide management. It is the combination of clinical features and level that is important.

Dose

• Greater than 125 mg/kg body weight: likely toxicity is mild.
• Greater than 250 mg/kg body weight: likely toxicity is moderate.
• Greater than 500 mg/kg body weight: likely toxicity is severe, possibly fatal.

Symptoms

• Mild (nausea, vomiting, tinnitus).
• Moderate (hyperventilation and confusion).
• Serious (hallucinations, seizures, coma, cerebral oedema or pulmonary oedema).

Investigations

• Plasma salicylate concentrations: at 2 h after ingestion in symptomatic patients and 4 h in asymptomatic patients – and if raised, repeated every 2 – 4 hours until levels are falling and clinical symptoms improving
• Arterial blood gas: respiratory alkalosis – hyperventilation, metabolic acidosis – lactate
• ECG: widened QRS, AV block, ventricular arrhythmias
• Renal function and electrolytes (hypokalemia), FBC, coagulation studies (raised INR/PTR), urinary pH, and blood glucose

Management

• Consider oral activated charcoal (50 g for an adult, 1 g/kg for a child) if ingested more than 125 mg/kg body weight salicylate less than one hour previously.
• Gastric lavage if the patient has ingested more than 500 mg/kg body weight salicylate within one hour.
• Aggressive rehydration
• Identify and teat Electrolyte Abnormalities
  • give potassium if the plasma potassium falls below 4.0 mmol/L.Hypokalaemia should be corrected before giving sodium bicarbonate
  • Have a low threshold to give glucose
• Urinary alkalinization: Consider urine alkalinization (target urine 7.5 – 8.5) if the plasma salicylate concentration is above 500 mg/L (3.6 mmol/L) using the following regime: 225 mmol sodium bicarbonate (225 mL of 8.4% over 60 minutes or 1.5 L of 1.26% over 2 hours)
• Haemodialysis is the treatment of choice for severe poisoning and should be seriously considered in patients with:Plasma concentrations greater than 700 mg/L (5.1 mmol/L),Severe metabolic acidosis (pH below 7.2),Acute kidney injury,Congestive cardiac failure.Non-cardiogenic pulmonary oedema,Coma,Convulsions,CNS effects not resolved by correction of acidosis,Persistently high salicylate concentrations unresponsive to urinary alkalinisation
• Endotracheal intubation may be indicated for deteriorating mental status or acute lung injury,uncontrollable agitation.