Arterial carbon dioxide partial pressure (PaCO2) is an essential indicator of ventilation and respiratory function. It is routinely tested invasively by arterial blood gas analysis (ABGA) but recently developed miniaturized carbon dioxide tension sensors promise non-invasive and continuous transcutaneous PCO2 (PtcCO2) monitoring. We, the researchers at University Hospital, Basel, Switzerland, determined the accuracy of two PtcCO2 monitors (TOSCA 500 with Sensor 92, Linde Medical Sensors AG, Basel; and Sentec Digital Monitor with V-Sign Sensor, Sentec AG, Therwil) for measurement of single values and trends in PaCO2 in critically ill patients, using ABGA as a reference.