Calculate PAO2 given FiO2 0.60, PB 760 mmHg, PH2O 47 mmHg, PaCO2 40 mmHg, and RQ 0.8.

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Multiple Choice

Calculate PAO2 given FiO2 0.60, PB 760 mmHg, PH2O 47 mmHg, PaCO2 40 mmHg, and RQ 0.8.

The alveolar gas equation connects inspired oxygen to alveolar oxygen by accounting for CO2 removal. First find the inspired O2 tension: PIO2 = FiO2 × (PB − PH2O). With FiO2 0.60, PB 760 mmHg, and PH2O 47 mmHg, PIO2 = 0.60 × (760 − 47) = 0.60 × 713 = 427.8 mmHg. Then adjust for CO2 using PAO2 = PIO2 − (PaCO2 / R). With PaCO2 40 mmHg and RQ 0.8, PaCO2/R = 40 / 0.8 = 50. So PAO2 ≈ 427.8 − 50 = 377.8 mmHg, about 378 mmHg. This matches the given calculation, whereas the other values would result from rounding differently or omitting the CO2 term.

The alveolar gas equation connects inspired oxygen to alveolar oxygen by accounting for CO2 removal. First find the inspired O2 tension: PIO2 = FiO2 × (PB − PH2O). With FiO2 0.60, PB 760 mmHg, and PH2O 47 mmHg, PIO2 = 0.60 × (760 − 47) = 0.60 × 713 = 427.8 mmHg. Then adjust for CO2 using PAO2 = PIO2 − (PaCO2 / R). With PaCO2 40 mmHg and RQ 0.8, PaCO2/R = 40 / 0.8 = 50. So PAO2 ≈ 427.8 − 50 = 377.8 mmHg, about 378 mmHg. This matches the given calculation, whereas the other values would result from rounding differently or omitting the CO2 term.

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