Pulmonary gas exchange can be described equally well using non-invasive data. The simplicity of the non-invasive approach makes the method suitable for large-scale clinical use.

The system illustrates how mathematical models combined with decision theory can aid in the difficult compromises necessary when deciding on ventilator settings.

In cardiac patients requiring supplementary oxygen, the respiratory abnormality could, in our model, be best described by an increased Rdiff, not by an increased shunt value.

Oxygenation in 12 patients preoperatively, 2, 8 and 48 h after gynaecological laparotomy is described. Two patients were hypoxaemic (SaO2 <92%) 48 h postoperatively. When two different models of oxygen transport are fitted to patient data, high values of Rdiff or low values of fA2 describe the right shift in the FEO2/SaO2 curve seen in patients with oxygenation problems. These models fit patient data identically, and may be useful in quantifying postoperative hypoxaemia.