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HBO Dissolved O2 at 3 atm — FRCA Primary MCQ

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HardPhysiology - RespiratoryHBO Dissolved O2 at 3 atmFRCA Primary

At 3 atmospheres absolute while breathing 100% oxygen, PaO2 is about 298 kPa. Using a solubility coefficient of 0.023 mL O2/dL/kPa, what dissolved oxygen content is closest?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: B — 6.9 mL O2/dL, calculated as 0.023 multiplied by 298

The best answer is “6.9 mL O2/dL, calculated as 0.023 multiplied by 298”. At 3 atmospheres absolute, inspired oxygen pressure after water-vapour subtraction is about 298 kPa. Dissolved oxygen content is therefore 0.023 mL/dL/kPa × 298 kPa = 6.85 mL/dL, closest to 6.9 mL/dL. Hyperbaric oxygen can provide substantial dissolved oxygen even when haemoglobin carriage is impaired, although it does not replace definitive treatment of the underlying cause.

Reference: Resuscitation Council UK, Adult Advanced Life Support Guidelines 2025: https://www.resus.org.uk/cy/node/36438