Workup of acute hypoxemia

Cyanosis:

when >5 g/dL of deoxygenated Hb in vessels of skin/mucous membranes.

Central: ↓ SaO2 (pulm disease, shunt);

abnl Hb [metHb, sulfHb, COHb (not true cyanosis)]

Peripheral:

↓ blood flow → ↑ O2 extraction (eg, ↓ CO, cold, arterial or venous obstruction)