In a patient who has ingested aspirin, which acid-base disorder is most likely?

Ingestion of aspirin, especially in toxic doses, can lead to a specific acid-base disturbance primarily due to its effects on the respiratory center in the brain. Salicylates, the active ingredient in aspirin, have a direct stimulatory effect on the central nervous system, particularly the respiratory center. This increased stimulation leads to hyperventilation, which causes an excess loss of carbon dioxide (CO2) from the body.

When CO2 levels decrease, the carbonic acid in the blood also decreases, resulting in a rise in blood pH, which characterizes respiratory alkalosis. This is a key feature of salicylate toxicity because the hyperventilation is a compensatory mechanism triggered by the acidosis following the metabolic effects of aspirin, even though the patient may also have some degree of metabolic acidosis due to aspirin’s effects on cellular metabolism.

Thus, recognizing the direct stimulation of the respiratory center and its primary consequence of respiratory alkalosis is crucial for determining the likely acid-base disorder in a patient who has ingested aspirin. This knowledge helps in the evaluation and management of such patients effectively.