MLT GlobeChemistry: Acid-base & blood gases – page 4
63 Chemistry MCQs on Acid-base & blood gases with answers and explanations.
A diabetic with vomiting has Na 140, Cl 94, HCO3− 20 mmol/L (normal anion gap 12). Comparing change in anion gap with change in HCO3−, which additional disorder is present?
Answer: A. Metabolic alkalosis
AG = 140 − (94 + 20) = 26, a rise of 14, while HCO3− fell only 4. A delta ratio of 3.5 (above 2) means bicarbonate is higher than expected, showing a coexisting metabolic alkalosis from vomiting.
ID MG-CHE-0326 · Found a mistake? Report it
Blood gas: pH 7.40, pCO2 60 mmHg, HCO3− 36 mmol/L. How is this best interpreted?
Answer: C. Mixed respiratory acidosis and metabolic alkalosis
A normal pH with both pCO2 and HCO3− markedly abnormal in opposite directions indicates two primary disorders. Compensation rarely returns pH fully to 7.40, so this is not simple compensation.
ID MG-CHE-0329 · Found a mistake? Report it
At sea level (760 mmHg), breathing room air (FiO2 0.21), a patient has PaO2 70 mmHg and PaCO2 40 mmHg. Using PAO2 = FiO2 × (760 − 47) − PaCO2/0.8, the A–a gradient is about:
Answer: C. 30 mmHg
PAO2 = 0.21 × 713 − 40/0.8 = 149.7 − 50 = 99.7 mmHg. A–a gradient = 99.7 − 70 ≈ 30 mmHg, higher than normal for most adults, suggesting a gas exchange problem.
ID MG-CHE-0336 · Found a mistake? Report it
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