A 69-year-old woman is taking large amounts of aspirin for osteoarthritis, and now complains of ringing in her ears and nausea.For the above patient with new symptoms, select the most likely acid base disorder.
**Core Concept**
Metabolic acidosis is a condition characterized by an increase in the concentration of acid in the blood, often resulting from the accumulation of acidic metabolic byproducts. In this context, the patient's symptoms of ringing in the ears (tinnitus) and nausea, combined with a history of aspirin use, suggest a potential link to aspirin-induced metabolic acidosis.
**Why the Correct Answer is Right**
Aspirin, being an acetylated salicylate, inhibits the enzyme carbonic anhydrase, which is involved in the regulation of bicarbonate levels in the blood. By inhibiting this enzyme, aspirin leads to a decrease in bicarbonate reabsorption in the kidneys, resulting in an increase in urinary excretion of bicarbonate. This, in turn, causes a metabolic acidosis, characterized by a decrease in blood pH and bicarbonate levels. The patient's symptoms of tinnitus and nausea are likely due to the effects of metabolic acidosis on the auditory system and the gastrointestinal tract.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the clinical scenario described. Metabolic alkalosis is characterized by an increase in blood pH and bicarbonate levels, which is not consistent with the patient's symptoms and history of aspirin use.
* **Option B:** Respiratory acidosis is a condition characterized by an increase in carbon dioxide levels in the blood, often resulting from impaired ventilation or respiratory failure. This option does not accurately describe the patient's condition, which is more likely due to metabolic acidosis.
* **Option D:** Lactic acidosis is a type of metabolic acidosis characterized by an increase in lactate levels in the blood. While this option is related to metabolic acidosis, it is not the most likely diagnosis in this case, as there is no indication of tissue hypoxia or other conditions that would lead to lactic acidosis.
**Clinical Pearl / High-Yield Fact**
Aspirin-induced metabolic acidosis is a potential side effect of long-term aspirin use, particularly at high doses. This condition can be exacerbated by other factors, such as dehydration, renal impairment, or underlying metabolic disorders.
**Correct Answer: B. Metabolic acidosis**