Which one of the following is the example of metabolic acidosis with respiratory alkalosis –
First, I need to recall the different types of acid-base disorders. Metabolic acidosis is when there's a primary decrease in bicarbonate (HCO3-), leading to a low pH. Respiratory alkalosis is a primary decrease in CO2 due to hyperventilation, which raises pH. So the combination would be a mixed disorder where both processes are present.
Common causes of this combination could be something like sepsis, where there's lactic acidosis (metabolic acidosis) and hyperventilation (respiratory alkalosis) due to fever or pain. Another example might be diabetic ketoacidosis with concurrent hyperventilation. Wait, but in DKA, the body compensates by hyperventilating, which is part of the Kussmaul breathing. So that's a metabolic acidosis with respiratory compensation, not a mixed disorder. Wait, no—compensation is a single disorder, but if there's another process causing respiratory alkalosis on top of that, then it's a mixed disorder. But I think the question is looking for a scenario where both are primary.
Another possibility is a patient with chronic obstructive pulmonary disease (COPD) who has a superimposed metabolic acidosis, but that's usually a respiratory acidosis with metabolic compensation. Not the mix here. Maybe a patient with salicylate toxicity? Salicylates cause both metabolic acidosis and respiratory alkalosis due to direct stimulation of the medullary respiratory center. Oh, right! Salicylate overdose is a classic example of a mixed acid-base disorder: metabolic acidosis from lactic acid and respiratory alkalosis from hyperventilation.
Alternatively, could it be a case of multiple organ failures where both processes are present? But the most classic example is salicylate toxicity. Let me confirm that. Salicylates (aspirin) cause a mixed metabolic acidosis and respiratory alkalosis. Yes, that's a high-yield point. So the correct answer would be salicylate poisoning. Therefore, if one of the options is salicylate toxicity, that's the answer. The other options might include things like DKA, which is metabolic acidosis with respiratory compensation (not a mixed disorder), or COPD exacerbation (respiratory acidosis with metabolic compensation), or maybe something like hyperkalemia, which isn't related. So the key is to identify the mixed disorder where both primary processes are present. So the correct answer is salicylate toxicity.
**Core Concept**
This question tests the understanding of mixed acid-base disorders, specifically the combination of **metabolic acidosis** (primary decrease in HCO₃⁻) and **respiratory alkalosis** (primary decrease in PaCO₂). Such combinations occur when two distinct pathophysiological processes coexist, rather than a compensatory response.
**Why the Correct Answer is Right**
A classic example is **salicylate (aspirin) toxicity**, which causes metabolic acidosis due to lactic acid and ketone accumulation. Simultaneously, salicylates directly stimulate the medullary respiratory center, inducing hyperventilation (respiratory alkalosis).