A pilot study comparing the zero-heat-flux temperature monitoring device to oesophageal temperature monitoring in orthopaedic surgery.

a) Description of the device. The study will compare the zero heat flux monitoring device (Bair Hugger™, 3M, St Paul, MN) to oesophageal temperature monitoring (DeRoyal™, Powell, TN . The zero-heat-flux device (Bair Hugger™, 3M, St Paul, MN) measures tissue temperature at 1-2cm below the skin surface of the forehead, and this is considered to approximate core temperature. The device is comprised of a thermal insulator placed on the skin, and covered by an electric heater. Heat flow through the insulator is eliminated by the servo-control of the heater, so that the heater and skin temperature becomes equal. Oesophageal temperature monitoring will be achieved by utilising a temperature probe inserted utilizing videolargyngoscopy to a distance of 15cm to ensure placement in the oesophagus at the time of intubation. b) Procedures Preoperative phase: On arrival to the pre-operative holding area, and prior to the induction of anaesthesia, the Research Nurse will attach the zero heat flux monitoring Bair Hugger™ device to the forehead, above the orbital ridge. After a ramp-up time of 3 minutes, temperature data will be retrieved from the control unit at 15 minute intervals by the research assistant (Research Nurse). Device failure and other adverse events will be recorded. Intraoperative phase: after transfer to the operating theatre, and during induction of anaesthesia, an oesophageal temperature monitoring (DeRoyal™) probe will be inserted in the distal oesophagus near the left atrium by the study anaesthetist. After adequate measurement depth is confirmed, the probe will be secured with the endotracheal tube. Standard monitoring, including electrocardiogram (ECG), pulse oximetry and non-invasive blood pressure (NIBP) will also be attached, as per usual care. General anaesthesia will commence in accordance with the study anaesthetic protocol developed in agreement with anaesthetic medical staff. Bladder temperature monitoring will be conducted via the indwelling urinary catheter, only if forming part of routine planned care for each participant. All patients will be covered with a warmed cotton blanket, receive fluid warming to 38.5°C via fluid warmer and full or partial body forced air warming, dependent upon surgical site, commencing at 47°C and then automatically decreasing to 45°C , as per the study protocol (and as per the normal operating function of the Covidien Warm Touch™ forced air warmer). Ambient temperature will be recorded. Postoperative phase: zero-heat-flux monitoring will continue upon transfer to the Post Anaesthetic Care Unit (PACU) and data will be recorded upon admission by the Research Nurse. Ambient temperature, warming interventions and acceptability of the device (from the patient’s perspective) will be assessed. c) Who will deliver the intervention The Research Nurse will attach the zero heat flux device and the anaesthetist will insert the oesophageal temperature monitoring probe. d) Mode of delivery Not applicable - see details above. e) Number of times intervention delivered & over what period of time. The zero heat flux device is attached preoperatively and will remain in place until admission to the Post Anaesthetic Care Unit. Oesophageal temperature monitoring remains in place only during general anaesthesia. f) Setting where the intervention occurs In the perioperative suite: in the preoperative holding area, through surgery and into the Post Anaesthetic Care Unit. g) Strategies used to assess adherence to the intervention Details of insertion and attachment of devices, as well as device failure, will be recorded.