Locally weighted scatterplot smoothing (lowess) curve showing the relationship between arterial oxygen value (PaO
) and predicted 6-month mortality. Predicted risk of death showed good performance in predicting actual mortality with an area under the curve (AUC) of 0.869 and R
2 of 0.422. A clear association between increased risk of death and low (approximately <11 kPa) PaO2 or values very high (approximately >42 kPa) PaO2 values was noted. The predicted probability of death is calculated using the following variables: acute physiology and chronic health evaluation II (APACHE II) index independent of oxygenation (AP2no-ox), admission year (before or after 2007), emergency operation, intracranial pressure monitoring, controlled hypothermia and platelet count.