A 48-year-old man is ventilated for severe pneumonia. ABG on FiO2 0.5, PEEP 10: pH 7.38, PaO2 11.5 kPa, PaCO2 5.2 kPa, HCO3 23 mmol/L. The alveolar-ar...

Question

A 48-year-old man is ventilated for severe pneumonia. ABG on FiO2 0.5, PEEP 10: pH 7.38, PaO2 11.5 kPa, PaCO2 5.2 kPa, HCO3 23 mmol/L. The alveolar-arterial (A-a) gradient is calculated. PIO2 = FiO2 × (Patm - PH2O) = 0.5 × (101.3 - 6.3) = 47.5 kPa. PAO2 = PIO2 - (PaCO2/RQ) = 47.5 - (5.2/0.8) = 41.0 kPa. A-a gradient = PAO2 - PaO2 = 41.0 - 11.5 = 29.5 kPa. What does this elevated A-a gradient indicate?

Accepted Answer

The elevated A-a gradient indicates impaired gas exchange at the alveolar-capillary level - caused by V/Q mismatch, shunt, or diffusion impairment; the normal A-a gradient on room air is

Answer

Normal gas exchange

Answer

Hypoventilation only

Answer

The calculation is incorrect

Answer

A-a gradient has no clinical utility

uk-fficm MCQ (SBA): A-a Gradient Interpretation