In-hospital mortality by partial oxygen pressure (PaO
) (kPa). Values were taken from blood gas analysis with lowest PaO2/fraction of oxygen in inspired air (FiO2) ratio in the first 24 h after intensive care unit (ICU) admission. The sizes of the circles represent the number of patients with the same PaO2 value. The curve represents the predicted mortality using the logistic regression equation in which the PaO2 value was incorporated using a spline function.