Salicylate Poisoning

Etiology and Pathophysiology

• Salicylates are found in aspirin-containing products, antidiarrheal medications, topical agents (such as keratolytics and sports creams), herbal products, and oil of wintergreen.
• Oil of wintergreen is highly concentrated and extremely lethal, containing $5$ g of salicylate in just $5$ mL of liquid.
• The acute toxic dose of salicylates is generally $>150$ mg/kg, with moderate to severe toxicity occurring at $>300$ mg/kg and $>500$ mg/kg, respectively.
• The primary pathophysiological mechanisms of salicylate toxicity include the direct stimulation of the respiratory center, the uncoupling of oxidative phosphorylation, the inhibition of the tricarboxylic acid cycle, and the stimulation of both glycolysis and gluconeogenesis.

Clinical Manifestations

• Salicylate poisoning is broadly categorized into acute and chronic ingestions, with acute toxicity being much more prevalent in pediatric patients.
• Significant insensible fluid losses occur due to vomiting, diaphoresis, tachypnea, and heat generated from the uncoupling of oxidative phosphorylation.

Diagnostic and Laboratory Evaluation

• Initial evaluation requires an arterial blood gas (ABG) analysis, serum glucose, complete blood count, renal function tests, liver transaminases, coagulation parameters, and an electrocardiogram.
• Serial serum salicylate levels must be drawn every $2-4$ hours until they are consistently downtrending (three consecutive levels $<30$ mg/dL and decreasing by at least $10-20$ each time) because absorption is highly erratic and often delayed.
• An acetaminophen level should be checked in all patients presenting with intentional salicylate overdose, as co-ingestions are common.
• A chest radiograph is indicated for any patient with respiratory distress to screen for noncardiogenic pulmonary edema.
• The Done nomogram is of poor predictive value and should not be utilized for clinical management.

Emergency Management

Decontamination and Supportive Care

• Gastric decontamination with activated charcoal ($1$ g/kg) is recommended for patients presenting soon after acute ingestion.
• Repeat doses of activated charcoal may be beneficial due to the delayed and erratic absorption profile of salicylates.
• Whole-bowel irrigation may be considered if there is a suspicion of bezoar formation from enteric-coated preparations, especially if serum levels persistently rise.
• Aggressive volume resuscitation with intravenous crystalloids is critical to replace the massive insensible fluid deficits.
• Parenteral glucose should be administered to any salicylate-poisoned patient with altered mental status to treat profound neuroglycopenia, which can be present even with normal peripheral serum glucose levels.

Urinary Alkalinization

• Urinary alkalinization is the primary modality for enhancing salicylate elimination; it requires administering a sodium bicarbonate infusion at approximately $2$ times the maintenance fluid rate.
• The initial dosage is a $1-2$ mEq/kg bolus of sodium bicarbonate, followed by a continuous infusion.
• The therapeutic goal is to achieve a urine $pH$ of $7.5-8.0$ and a serum $pH$ of $7.45-7.55$.
• Alkalinization traps the ionized form of salicylate within the renal tubules, facilitating its excretion, and prevents uncharged salicylate molecules from crossing the blood-brain barrier, thereby preventing cerebral edema.
• Potassium must be aggressively monitored and supplemented within the bicarbonate infusion, as hypokalemia directly prevents the alkalinization of the urine.

Indications for Hemodialysis

• Hemodialysis rapidly removes salicylates and corrects severe metabolic and electrolyte derangements.
• Serum salicylate concentrations alone should not dictate the need for hemodialysis; the decision must integrate the overall clinical status.