The alveolar-arterial oxygen pressure gradient is an
indicator of the ease of oxygen transfer from the alveoli to
the pulmonary blood. An alveolar-arterial oxygen pressure
gradient .10 mmHg is an indicator of poor oxygen transfer
due to ventilation–perfusion mismatching, diffusion impairment,
or right-to-left vascular shunt.12 The alveolar-arterial
oxygen pressure gradient is calculated using the following
formulae: