A patient with anxiety-induced hyperventilation doubles her minute alveolar ventilation while her metabolic CO2 production remains constant. Her new PaCO2 will be approximately:

• A 80 mmHg
• B 60 mmHg
• C 40 mmHg
• D 20 mmHg ✓

Explanation

Alveolar PCO2 varies inversely with alveolar ventilation for a given metabolic CO2 production, expressed as PACO2 proportional to VCO2 divided by VA. Doubling alveolar ventilation halves PaCO2 from 40 mmHg to about 20 mmHg, producing acute respiratory alkalosis. Options B and A describe hypoventilation states, which reduce ventilation and raise PaCO2 above normal rather than lowering it.

Reference: West's Respiratory Physiology: The Essentials, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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