Salicylates, principally acetylsalicylic acid (ASA or aspirin), remain a common cause of poisoning morbidity and mortality. In 2021 America’s Poison Centers recorded 18,309 cases mentioning ASA and it was among the top 25 causes of poisoning deaths.¹ Emergency physicians should be aware of 10 pitfalls in assessing and treating patients with salicylate poisoning.

Done With the Done Nomogram?

In the 1960s, A.K. Done published a nomogram to identify patients at high-risk for severe outcomes from salicylate poisoning. The graph was based on a patient’s serum salicylate concentration.² Later research found that the nomogram performed poorly for this purpose.³ Advanced age, high respiratory rate, and elevated lactate concentration appear to be better in identifying severe salicylate poisoning.⁴

Critical action 1: Do not use the Done nomogram to assess salicylate toxicity.

Critical action 2: Assess severity of poisoning with the patient’s age, the respiratory rate, and the lactate concentration in addition to the salicylate concentration.

Units Matter

Many medical laboratories measure serum salicylate using a colorimetric ferric nitrate or ferric chloride assay^5,6 and can report this information in different units. While other

countries use SI units (mmol/L), the two most common units in the U.S. are μg/mL (mg/L) and mg/dL. 1 mg/dL = 10 μg/mL = 10 mg/L = 0.072 mmol/L. A salicylate concentration of 100 μg/mL is at the lower end of the therapeutic range, but a salicylate concentration of 100 mg/dL is lethal without emergency dialysis.⁷ Henceforth, we express salicylate concentration in mg/dL.

Critical action: Know the units that your hospital laboratory uses.

Mind the Ions, Not the Gap

Salicylate is the “S” in MUDPILES, a mnemonic for causes of high anion gap metabolic acidosis. Salicylate ions sometimes interfere with the ion-selective electrodes of chemistry analyzers and may overestimate chloride ion concentration. This can cause pseudohyperchloremia, which can suppress the anion gap.^8–10 The anion gap may even be negative.^11–13

Critical action 1: Pay attention to a low bicarbonate level.

Critical action 2: Ignore a normal or low anion gap if the chloride is high.

Dextrose for Euglycemic Delirium

The brain needs glucose for energy. Salicylate uncouples oxidative phosphorylation—largely by drawing protons away from the mitochondrial intermembrane space. As this occurs, the brain consumes glucose more quickly while producing less adenosine triphosphate (ATP) and generating excess heat. This produces hypoglycorrhachia (low CSF glucose despite normal blood glucose), even when the blood glucose is normal.

Experiments in salicylic-acid-poisoned mice demonstrated that the mice had hypoglycorrhachia with relatively normal blood glucose.¹⁴ Case reports in salicylate poisoned children undergoing lumbar puncture due to clinical features resembling sepsis further illustrate hypoglycorrhachia.^15,16 While children will often have hypoglycemia with severe salicylate poisoning, adults may maintain normal blood glucose due to glycogenolysis. Additional animal experiments showed rats given supplemental dextrose consistently survived an LD50 dose of salicylate.¹⁷

Glucose supplementation may quickly improve delirium and confusion in salicylate poisoned patients.¹⁸

Critical action: Give supplemental dextrose to any salicylate poisoned patient with altered mental status even if the blood glucose concentration is normal.

Hemodialysis

Salicylate has the four properties of highly dialyzable substances (low molecular weight, water soluble, small volume of distribution, and low protein binding in overdose).¹⁹ The Extracorporeal Treatments In Poisoning group recommends hemodialysis for patients with salicylate ≥100 mg/dL or ≥90 mg/dL in the presence of impaired kidney function (defined as Stage 3b or higher chronic kidney disease, serum creatinine ≥ 2 mg/dL (176 μmol/L) in most adults, or serum creatinine ≥1.5 mg/dL (132 μmol/L) in elderly patients).¹⁹ These thresholds, however, may be too high. Warrick et al. reviewed 29 years of salicylate deaths reported to America’s Poison Centers and found that half of the fatal cases had ante-mortem concentrations below 100 mg/dL.⁷ A better threshold for considering dialysis would be salicylate more than 60 mg/dL.

Critical action: Consult your Nephrology colleagues early when the salicylate level approaches 60 mg/dL, or rises despite optimal treatment, or if the patient’s condition worsens regardless of salicylate concentration.

Potassium

Salicylate poisoned patients typically have hypokalemia on initial presentation.^20–22 Sodium bicarbonate infusion and IV fluid resuscitation, needed to alkalinize the blood and urine, tend to exacerbate the already low serum potassium concentration. Supplemental potassium is necessary to replenish lost potassium and to alkalinize the urine successfully.

Critical action 1: Replete potassium generously with IV and oral potassium salts.

Critical action 2: Measure the urine pH periodically to confirm urinary alkalinization.

Critical action 3: Monitor salicylate concentration, basic metabolic panel, and venous blood gases as frequently as every 2 hours until the patient clearly improves.

Acetazolamide

Acidosis favors salicylate protonation to un-ionized salicylic acid, which more easily crosses the blood brain barrier than salicylate. Early work in children in the 1950s indicated that acetazolamide alkalinized the urine, increased urinary excretion of salicylate, and increased salicylate clearance from blood.^23,24 In a report of three cases, one child died and had cerebral edema at autopsy.²³ Children in a larger cohort generally survived but had a mean serum salicylate of 38.7 mg/dL. Experimental animal evidence confirmed the increased urinary excretion of salicylate but also found that acetazolamide increased salicylate concentrations in both CSF and brain tissue and increased mortality in rats.^25,26 In effect, blood salicylate concentration falls in part due to increased delivery of salicylate to the brain—the target organ of salicylate toxicity.

Critical action: Do not use acetazolamide in the treatment of salicylate poisoning.

Mechanical Ventilation

Patients with salicylate poisoning may develop metabolic acidosis with respiratory alkalosis. Although early respiratory alkalosis may be a direct effect of salicylate on the medullary neurons controlling respiration, later hyperventilation is a compensatory reaction to worsening acidosis.²⁷ When a salicylate poisoned patient’s respiratory status leads you to consider intubation, give priority to emergency hemodialysis if available.¹⁹ In fact, such patients may not tolerate sedation and paralysis during rapid sequence induction and intubation because those actions can eliminate respiratory compensation and worsen acidosis. Case reports illustrate abrupt cardiac arrest in the minutes following intubation.^16–18 Failure to hyperventilate after intubation likely contributes to this.

Critical action 1: When considering intubation, call for emergency hemodialysis, if available.

Critical action 2: If intubation is unavoidable, pre-treat with sodium bicarbonate and match the pre-intubation respiratory rate.

Persistence of Aspirin in the Upper GI Tract

Aspirin tablets can persist in the stomach and may coalesce to form a bezoar.^21,31–33 This results in delayed or ongoing absorption of aspirin. The earliest clue may be a rising or persistently elevated salicylate level despite optimal treatment with IV fluids, sodium bicarbonate, and potassium replacement.

Critical action 1: Monitor salicylate, basic metabolic panel, and venous blood gases as frequently as every 2 hours until the patient clearly improves.

Critical action 2: Give repeated doses of activated charcoal unless endoscopy is available to remove retained pills or bezoars from stomach.

Recognizing Chronic Salicylate Poisoning

Some older adults may use over-the-counter ASA to self-treat arthritis or other persistent pain. Chronic salicylate toxicity can mimic sepsis with insidious onset of hyperthermia, confusion, tachycardia, tachypnea, metabolic acidosis, and acute kidney injury.^34–37 Recognizing this possibility early can prevent morbidity and mortality, especially in older patients.³⁸

Critical action 1: Include salicylism in your differential diagnosis of an older adult who is unwell without apparent cause.

Critical action 2: Inquire about the patient’s use of over-the-counter medications.

Dr. Hebbard is an emergency physician, medical toxicology fellow, and biochemist.

Dr. Mullins is a professor of emergency medicine and faculty member of the medical toxicology fellowship at Washington University School of Medicine.

References

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