Comparison of the Accuracy and Precision of a Zero Heat Flux Thermometer (SpotOnTM) Versus Pulmonary Artery Temperature Measurement in Patients Undergoing On-pump Heart Surgery: a Prospective, Multicentre, Observational Study.

Anesthesia will be induced with fentanyl, propofol and rocuronium and maintained with sevoflurane and fentanyl or sevoflurane and remifentanil infusion. Hypotension after induction of anesthesia will be treated primarily with phenylephrine or ephedrine and secondarily with norepinephrine infusion.

After induction of anesthesia a PAC (Edwards Lifescience, Thermodilution Paceport Catheter 931F75, 7.5F (2.5 mm) 110 cm) will be inserted in the pulmonary artery and connected to a Vigilance 2-monitor. Core temperature at the tip of the PAC will be measured every minute and displayed on the monitor. Two SpotOn™ ZHF temperature monitoring probes (3M, Model 370 Temperature Monitoring System, St. Paul, MN) will be fixed on the skin of the left and right side of the forehead above the eyebrow before induction of anesthesia. These devices also measured core temperature every minute and displayed the values on two display screens. In addition a temperature-sensing indwelling urinary catheter (CovidienTM, Mon-a-ThermTM, Foly Catheter with temperature sensor 400TM) will be placed after induction of anesthesia to allow continuous drainage of urine and continuous measurement of body temperature.

Core temperatures measured by PAC, ZHF-thermometer and bladder thermometer will be recorded with an interval of 1 minute.

In all patients the core temperature are allowed to drop until going on CPB. There will be no no external warming or infusion warming before CPB. At initiation of CPB measurements will stop because during CPB core temperatures measured with PAC does not produce an accurate estimate of core temperature.