8 minute read
Ventilation and oxygenation are different failures
PaCO2 is ventilation: the pump (drive, muscles, mechanics). PaO2 is oxygenation: the exchanger (V/Q matching, shunt, diffusion). The A-a gradient separates them: hypoxia with a normal gradient is hypoventilation or altitude; a wide gradient means the lung itself is involved.
Why chronic retainers are titrated, not flooded
In chronic hypercapnia, uncontrolled oxygen worsens CO2 through V/Q effects and the Haldane shift more than through 'lost drive' folklore, but the ward rule is the same either way: titrate to 88 to 92 percent and follow the gas, not the folklore.
Pearls
- The bicarbonate is the gas's memory: it records how long the CO2 has been high.
- Work of breathing trends beat any single saturation reading.
Connected