Henderson-Hasselbalch equation for bicarbonate buffer: pH = 6.1 + log([HCO3-] / 0.03 × PaCO2). If HCO3- = 12 mEq/L and PaCO2 = 24 mmHg, what is the approximate pH?
- A 7.40
- B 7.32 ✓
- C 7.20
- D 7.52
Correct answer: B. 7.32
Explanation
pH = 6.1 + log(12 / [0.03 × 24]) = 6.1 + log(12 / 0.72) = 6.1 + log(16.67) = 6.1 + 1.22 = 7.32. This represents a high-AG metabolic acidosis with appropriate respiratory compensation (Winters' formula: expected PaCO2 = 1.5 × 12 + 8 ± 2 = 26 ± 2 mmHg; actual 24 mmHg is within range). The calculation confirms acidaemic pH with bicarbonate and PCO2 falling proportionally.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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