Salicylate Overdose

Essentials of Diagnosis

• Tachypnea, altered mental status

• Metabolic acidosis

• Typical arterial blood gases reveal respiratory alkalosis and metabolic acidosis

• Elevated salicylate level diagnostic

General Considerations

• Salicylates (eg, aspirin, methyl salicylate, bismuth subsalicylate) are found in a variety of over-the-counter and prescription medications

• Salicylates uncouple cellular oxidative phosphorylation, resulting in anaerobic metabolism and excessive production of lactic acid and heat, and interfere with several Krebs cycle enzymes

• A single ingestion of more than 200 mg/kg of salicylate can cause intoxication

• Poisoning may also occur as a result of excessive dosing over several days

• Although the half-life of salicylate is 2–3 h after small doses, it may increase to 20 h or more in patients with intoxication

Symptoms and Signs

• Acute ingestion

  • Nausea and vomiting, occasionally with gastritis

• Moderate intoxication

  • Hyperpnea (deep and rapid breathing), tachycardia, and tinnitus

• Serious intoxication

  • Agitation, confusion, seizures

  • Cardiovascular collapse, pulmonary edema, hyperthermia

  • Death

Differential Diagnosis

• Other causes of anion gap acidosis

  • Alcoholic ketoacidosis

  • Metformin toxicity

  • Isoniazid poisoning

  • Iron poisoning

  • Methanol or ethylene glycol toxicity

  • Carbon monoxide poisoning

• Acetaminophen poisoning (common coingestion)

Laboratory Tests

• Diagnosis is suspected in any patient with an anion gap metabolic acidosis and is confirmed by measuring the stat serum salicylate level

• Patients with serum salicylate levels > 100 mg/dL (1000 mg/L or 7.2 mcmol/L) after an acute overdose are more likely to have severe poisoning

• Patients with subacute or chronic intoxication may suffer severe symptoms with serum salicylate levels of only 60–70 mg/dL (4.3–5 mcmol/L)

• Arterial blood gases typically reveal a respiratory alkalosis with an underlying metabolic acidosis

• Prothrombin time is often elevated owing to salicylate-induced hypoprothrombinemia

• Central nervous system intracellular glucose depletion can occur despite normal measured serum glucose levels

Medications

Emergency and supportive measures

• Activated charcoal

  • Administer 60–100 g orally or via gastric tube, mixed in aqueous slurry

  • Do not use for comatose or convulsing patients unless it can be given by gastric tube and the airway is protected by a cuffed endotracheal tube

  • Extra doses of activated charcoal may be needed in patients who ingest more than 10 g of aspirin (desired ratio of charcoal to aspirin: ~10:1 by weight)

  • Although extra doses cannot always be given as a single dose, they may be administered over the first 24 h in divided doses every 2–4 h along with whole bowel irrigation

• Give glucose-containing fluids to reduce the risk of cerebral hypoglycemia

• Treat metabolic acidosis with intravenous sodium bicarbonate

  • This is critical because acidosis (acidemia, pH < 7.40) promotes greater entry of salicylate into cells, worsening toxicity

Specific treatment

• Alkalinization of the urine enhances renal salicylate excretion by trapping the salicylate anion in the urine

  • Add 100 mEq (2 ampules) of sodium bicarbonate to 1 L of 5% dextrose in 0.2% saline

  • Infuse intravenously at a rate of ~150–200 mL/h

• Unless the patient is oliguric or hyperkalemic, add 20–30 mEq of potassium chloride to each liter of intravenous fluid

• Patients who are volume depleted often do not produce an alkaline urine (paradoxical aciduria) unless potassium is given

Therapeutic Procedures

• Hemodialysis may be lifesaving and is indicated for patients with

  • Severe metabolic acidosis

  • Markedly altered mental status

  • Significantly elevated salicylate levels (> 100–120 mg/dL [1000–1200 mg/L or 7.2-8.6 mcmol/L] after acute overdose or > 60–70 mg/dL [600–700 mg/L or 4.3–5 mcmol/L] with subacute or chronic intoxication)

Follow-Up

• Monitor serum salicylate level every 2 h initially to determine if it is continuing to rise

• Patients with massive ingestion (eg, > 100 tablets)

  • May have delayed absorption

  • May require prolonged observation until levels fall into normal range

Complications

• Sudden and severe deterioration can occur after rapid sequence intubation and controlled ventilation if the pH is allowed to fall during the apneic period

When to Admit

• Suicidal ingestion

• History of massive ingestion with rising levels

• Evidence of significant intoxication

  • Altered mental status

  • Metabolic acidosis

  • Elevated salicylate level

Prognosis

• Good if blood pH is maintained above 7.4 and hemodialysis is promptly performed in patients with serious toxicity