A 34-year-old woman is brought to the emergency department by ambulance due to nausea, dizziness, and confusion. Her boyfriend arrives with her and says that he found her lying on the bed next to an empty bottle of aspirin tablets. When asked about the potential ingestion, the patient admits to swallowing a "bunch of aspirin pills a little more than 12 hours ago" after coming home from work. She also describes hearing "an annoying buzzing sound that won't stop." Temperature is 38.3 C (101 F) and pulse is 102/min. She appears agitated and confused. Which of the following sets of laboratory results is most likely to be found in this patient?

Question

Quizplus · Accepted Answer

Acute salicylate intoxication typically presents with nausea/vomiting, dizziness, confusion, tinnitus (eg, ringing/buzzing sound), fever, and tachypnea within several hours after ingestion. Two different acid-base abnormalities are characteristic: Primary respiratory alkalosis occurs because salicylates directly stimulate the medullary respiratory center, resulting in increased ventilation and loss of CO₂ in the expired air. Primary anion gap metabolic acidosis develops because toxic salicylate levels increase lipolysis, uncouple oxidative phosphorylation, and inhibit the citric acid cycle. This results in the accumulation of unmeasured organic acids in the blood (eg, ketoacids, lactate), increasing the anion gap. Therefore, salicylate toxicity classically presents with a mixed acid-base disturbance, with arterial blood gas sometimes showing a pH within the normal range as the 2 primary disturbances shift the pH in opposite directions. There is low serum HCO₃^- due to primary metabolic acidosis and low PaCO₂ due to both respiratory compensation for the metabolic acidosis and the primary respiratory alkalosis. Because of the mixed disturbance, the PaCO₂ is lower than expected for respiratory compensation alone (ie, per Winters' formula the expected PaCO₂ due to respiratory compensation is ~23 mm Hg, but the primary increase in central respiratory drive pushes PaCO₂ even lower). (Choice A) Low pH with elevated PaCO₂ is consistent with primary respiratory acidosis, which can occur with the respiratory depression seen with opioid overdose. HCO₃^- is slightly elevated, which is consistent with the small degree of metabolic compensation that occurs in the acute setting; full metabolic compensation requires approximately 72 hours. (Choice C) These values are consistent with normal acid-base status. (Choice D) High pH with elevated HCO₃^- represents primary metabolic alkalosis, which can occur with intractable vomiting. PaCO₂ is elevated and consistent with appropriate respiratory compensation. (Choice E) High pH with low PaCO₂ and near normal HCO₃^- represent primary respiratory alkalosis with minimal metabolic compensation. This can occur with any cause of acute hyperventilation (eg, panic attack). Educational objective: Salicylate intoxication should be suspected in patients with the triad of fever, tinnitus, and tachypnea. Salicylates both stimulate central respiratory drive to cause primary respiratory alkalosis and disrupt cellular metabolism to cause primary anion gap metabolic acidosis. Therefore, toxicity classically presents with a mixed acid-base disturbance and a blood pH sometimes within the normal range. __________ References: Salicylate intoxication: a clinical review. (http://www.ncbi.nlm.nih.gov/pubmed/19641282)

A 34-Year-Old Woman Is Brought to the Emergency Department by Ambulance