TOPICS: Gas exchange, hypoxemia, partial pressure of arterial oxygen (PaO2), oxygen content equation, hypoventilation, A-a gradient, V/Q mismatch, diffusion, hypoxia, partial pressure of oxygen in the alveoli (PAO2), pressure gradient, right shift, perfusion (Q), shunt, hemoglobin-oxygen dissociation curve, V/Q ratio, diffusion limitation, 2,3-diphosphoglyceric acid (2,3-BPG), left shift
