1. The iso-shunt diagram, illustrating the relationship between PaO2 and FIO2 in the presence of a shunt corresponding to different percentages of total lung blood flow.
The iso-shunt diagram, illustrating the relationship between PaO2 and FIO2 in the presence of a shunt corresponding to different percentages of total lung blood flow. Note the near linear relationship between PaO2 and FIO2in the absence of shunt. With increasing shunt fractions, the change in PaO2 with increasing FIO2 is much more flat. Hence, a large increase in FIO2 results in little change in PaO2. For a shunt >30% of cardiac output, even a FIO2 of 1.0 fails to result in a PaO2 of 100 mmHg (13.3 kPa). Modelling is based on a haemoglobin concentration of 14 g·dL−1, PaCO2 of 40 mmHg (5.3 kPa) and an arterial–mixed venous oxygen content difference (Ca–v¯O2) of 5 mL·dL−1. For a glossary of terms, see table 1. Adapted from [15].
Johan Petersson, and Robb W. Glenny Eur Respir J 2014;44:
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