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Winter's Formula — FRCA Primary MCQ

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HardPhysiology - RespiratoryWinter's FormulaFRCA Primary

Winter's formula predicts the expected PaCO2 compensation in metabolic acidosis as:

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Correct answer: C — PaCO2 = (1.5 × HCO3-) + 8 ± 2 (in mmHg)

Winter's formula: expected PaCO2 (mmHg) = (1.5 × [HCO3-]) + 8 ± 2. If measured PaCO2 is higher than predicted → concurrent respiratory acidosis. If lower → concurrent respiratory alkalosis. Example: HCO3- = 12 mmol/L → expected PaCO2 = (1.5 × 12) + 8 = 26 ± 2 mmHg. This helps identify mixed acid-base disorders.

Reference: Power Kam 2018 Principles of Physiology for the Anaesthetist