Clinical meaning
Salicylate toxicity occurs from aspirin overdose or chronic excessive use, causing a complex metabolic disturbance with a characteristic mixed respiratory alkalosis and metabolic acidosis. Salicylates directly stimulate the medullary respiratory center causing hyperventilation and respiratory alkalosis (primary early finding). Simultaneously, salicylates uncouple oxidative phosphorylation, inhibit Krebs cycle enzymes, and cause accumulation of organic acids producing anion gap metabolic acidosis. As toxicity progresses, metabolic acidosis predominates and the compensatory respiratory alkalosis becomes insufficient. Salicylates also cause hyperthermia from uncoupled oxidative phosphorylation, tinnitus from cochlear damage, and non-cardiogenic pulmonary edema. Acute toxicity occurs with ingestion > 150 mg/kg; levels > 40 mg/dL at 6 hours post-ingestion indicate significant toxicity; levels > 100 mg/dL indicate potentially lethal toxicity. Alkalinization of urine with sodium bicarbonate enhances renal salicylate excretion by ion trapping.
Exam relevance
Risk factors: - Intentional aspirin overdose in suicide attempts - Chronic salicylate therapy in elderly with renal impairment - Concurrent use of multiple salicylate-containing products - Oil of wintergreen ingestion (concentrated methyl salicylate) - Inability to recognize early symptoms (tinnitus, GI upset)