Abstract: The invention relates to a method and an apparatus for estimating a PaO2 value for a patient subject to extra corporeal circulation by means of an oxygenator. The method comprises the steps of measuring a PexO2 value in the exhaust gas of the oxygenator and calculating the estimated PaO2 based on the PexO2 value. Advantageously, the estimated PaO2 value pressure is calculated as the difference between the PexO2 value and a correction value, which is calculated in dependency of at least one measurement parameter selected from the following group: PexO2, an arterial temperature value, the blood flow through the oxygenator, venous oxygene saturation, arterial haemoglobin concentration, the fraction (FiO2) of oxygen in the gas supplied to the oxygenator, and the gas flow supplied to the oxygenator.

Abstract: The invention relates to a method and an apparatus for estimating a PaCO2 value for a patient subject to extracorporeal circulation by means of an oxygenator. The method comprises the steps of measuring a PexCO2 value in the exhaust gas of the oxygenator and the patient's arterial blood temperature value Ta, using a temperature sensor arranged in the oxygenator. The estimated PaCO2 value is then calculated, based on the measured PexCO2 value and the arterial temperature measurement. Advantageously, an average value determined from a predetermined number of recent PexCO2 values is used in the calculation. The calculation is performed by adding a correction term to the PexCO2 value, which is composed of a temperature dependent component and an offset component. The correction term may be adjusted by a user. The estimated PaCO2 value is presented on a display. A switch provides easy alteration between pH-stat mode and alpha-stat mode.